CA2821050A1 - Predator deterrent - Google Patents

Abstract

The present invention relates to an improved predator deterrent system, particularly for deterring predators of aquatic creatures such as fish in fish farms. In particular the invention provides a predator deterrent system for a submerged fish enclosure comprising: at least one trigger device configured to detect a predator in the vicinity of a fish enclosure; and configured to generate an alarm signal responsive to the detection of the predator; and at least one alarm device responsive to the alarm signal generated by the trigger device, the alarm device comprising at least one electrified enclosure section wherein upon receipt of an alarm signal generated by the trigger device at least one electrified enclosure section is powered. A further predator deterrent system for a submerged first enclosure comprising: a control means for controlling delivery of power to the at least one electrified enclosure section, a method of deterring predators, a method of manufacturing a predator deterrent system and a modular kit for a predator deterrent system are also described.

Description

PREDATOR DETERRENT
Field [0001] The present invention relates to improved predator deterrent systems and methods, particularly for deterring predators of aquatic creatures such as fish in fish farms. A modular predator deterrent system is also described.
Background

[0002] Our earlier patent GB2369025B ACE HOPKINS describes a type of scaring device for avoiding the predation of fish in fish farms. The disclosure of GB2369025B is incorporated herein by reference. In GB2369025, a motion detector is used to detect motion of fish in a fish growing enclosure, and activates an alarm responsive to the output of the motion detector for scaring the predators.

[0003] US4593648 and DE3219867 to MARZLUF describe an electrical fish scaring device for water inlet and extraction structures that uses main and opposing electrodes. The device uses pulsed d.c. voltage at an appropriate strength and pulse duration to create an electric field.

[0004] US4580525 MARZLUF describes an electric fish scaring device for water inlet and discharge plants that generates differing voltage pulses to scare away fish of varying sizes.

[0005] DE3441345 also to MARZLUF describes an electrical fishing scaring system for inlet and water extraction sites having a measurement electrode system to monitor current density or field strength in various measurement directions.

[0006] JP2007089449 SUDO describes a method and an apparatus for defending an object from shark attack, in which a power device is not required using two different kinds of materials having different potentials to generate an electric field in the seawater.

[0007] GB2472035 and GB2472037 CHAMBERS describe an open water fish farm that uses both bubbles and acoustic sounds to contain the fish without a need for nets or cages.

[0008] W09500016A1 JEFFERS describes an acoustic deterrent that uses increasing intensities of sound to deter a predator as it approaches a fish farm.

[0009] W02008129313, US8289812 and US20130021877 GOTZ
describe a system to elicit an acoustic startle response in targeted mammals.

[0010] W02011090925 DELACROIX describes a system that uses low frequency acoustic wavelengths (20-250Hz) to keep predators away from fish farms.

[0011] W0940007 FERRANTI describes a fish farm cage security system utilising bells attached to the cage for detecting tampering with one or more nets.

[0012] CN102792905 HONCHUAN describes a barrier-free way to allow ships to enter an area of water whilst at the same time keeping fish out of the same area using an electric field.

[0013] CN1059575 DEXIU describes a system for deterring fish from the belled mouth of the reservoir culvert, in which vertical and horizontal electrodes are buried.

[0014] CN1078597 DEXIU describes an electric fish barrier net, which has two rows of electrodes, the first row is low voltage and the second is high voltage. CN2355535 DEXIU describes an electric net for "tucking" fish comprising an electrode, a power transmission line, a supporting frame, a floater and a power source.

[0015] CN2702613 YU describes a deep water net cage containing an electrical circuit fault and breakage monitoring apparatus comprising a cover net detection circuit.

[0016] US20040174266 LARSEN describes a fish farming net having conductive wires integrated into the filaments of the net. If the net is broken, indicated by a broken conductor, an alarm is signalled.

[0017] RU2384061 TEODOROVICH describes a fishing sweep net that has electrodes powered from shore or from an electric station on a waterborne vehicle in which electric framing ropes create an electric field that controls the fish behaviour.

[0018] RU2304385 TEODOROVICH describes a trawling net envelope with electrodes located on it. Wires supply pulse current to generate an electric field that controls fish behaviour.

[0019] GB176096 GUNYON describes an invention in which fish behaviour is controlled by creating an electric field in the water between two electrodes. Electrodes may be placed on a net or a fishing line.

[0020] Acoustic deterrent devices and their affect on wildlife has been studied by Gordon, J. & Northridge, S. (2002) Potential impacts of Acoustic Deterrent Devices on Scottish Marine Wildlife. Scottish Natural Heritage Commissioned Report FO1AA404.

[0021] An acoustic deterrant device (universal scrammer US3, previ-ously versions US1, US2) is available from Ace Aquatec Ltd, UK.

[0022] Thomas Gotz describes "Aversiveness of Sound In Marine Mammals: Psycho-Physiological Basis, Behavioural Correlates and Potential Applications" in his thesis submitted for the degree of PhD at the University of St. Andrews in 2008, available at http://hdl.handle.net/10023/848.

[0023] Forrest et al describe "Evaluation of an Electric Gradient to Deter Seal Predation on Salmon Caught in Gill-Net Test Fisheries" in the North American Journal of Fisheries Management 29:885-894, 2009.

[0024] Hastie describes "Tracking marine mammals around marine renewable energy devices using active sonar" in SMRU Ltd report URN:
12D/328 to the Department of Energy and Climate Change. September 2012 (unpublished).

[0025] In a document published after the priority date of the present application, Milne et al describes "Behavioural responses of seals to pulsed, low-voltage electric fields in sea water (preliminary tests)", first published:
December 2012 (ISBN: 978-1-907266-51-5 published by the: Scottish Aquaculture Research Forum (SARF), available at: http://www.sarf.org.uk).

[0026] Some of the prior art provide predator deterrent systems.
Nevertheless, in view of the habituation of predators to deterrent systems, a more effective predator deterrent system is desirable. The present invention seeks to alleviate one or more of the problems presented by the above systems.
Statement of Invention

[0027] The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other im-provements.

[0028] In a first aspect the invention provides a predator deterrent system for a submerged fish enclosure comprising: at least one trigger device configured to detect a predator in the vicinity of a fish enclosure; and config-ured to generate an alarm signal responsive to the detection of the predator;
and at least one alarm device responsive to the alarm signal generated by the trigger device, the alarm device comprising at least one electrified enclosure section wherein upon receipt of an alarm signal generated by the trigger device at least one electrified enclosure section is powered.

[0029] In a further aspect, the invention provides a predator deterrent system for a submerged fish enclosure comprising: at least one electrified enclosure section; a control means for controlling delivery of power to the at least one electrified enclosure section.

[0030] In a further aspect, the invention provides a method of deterring predators for a submerged fish enclosure having at least one electrified enclosure section comprising: activating the at least one electrified enclosure section to deter predators.

[0031] In a further aspect, the invention provides a method of manufac-turing a predator deterrent system for a submerged fish enclosure comprising providing a predator deterrent system as described herein.

[0032] In a further aspect, the invention provides a modular kit for a predator deterrent system comprising at least one alarm device as described herein; at least one trigger device as described herein; wherein at least one alarm device comprises an electric enclosure alarm device having at least one electrified enclosure section.

[0033] Optionally the system comprises a control means for controlling delivery of power to the at least one electrified enclosure section.
Optionally, the at least one electrified enclosure section comprises two or more conduc-tors. Optionally, the at least one electrified enclosure section comprises a portion of an enclosure e.g. a portion of a net, a portion of a cage, a portion of permeable enclosure material.

[0034] Optionally, at least one electrified enclosure section comprises two or more conductors; and the control means is configured to supply power to one or more predetermined conductor(s), in the electrified enclosure section following removal of power from one or more preceding predeter-mined conductor(s) in the same electrified enclosure section.

[0035] Optionally, the conductors are grouped in at least two groups, each group comprising one or two or more conductor(s) and the control means is configured to supply power to the conductor(s) in one group follow-ing removal of power from the conductor(s) in another group. Optionally, the groups comprise 2 or 3 or 4 or 5 or 6 conductors.

[0036] Optionally, at least one electrified enclosure section comprises two or more groups of conductors, each group consisting of a pair of conduc-tors and when power is supplied to a group, a potential is applied between the pair of conductors in that group.

[0037] Optionally, the system comprises: two or more electrified enclosure sections; and the control means is configured to supply power to one or more predetermined electrified enclosure section(s) following removal of power from one or more predetermined preceding electrified enclosure section(s).

[0038] Optionally, the electrified enclosure sections are grouped in at least two groups, each group comprising one or two or more electrified enclosure section(s) and in which the control means is configured to supply power to the electrified enclosure section(s) in one group following removal of power from the electrified enclosure section(s) in another group. Option-ally, a group comprises 2 or 3 or 4 or 5 or 6 electrified enclosure sections.

[0039] Optionally, the electrified enclosure sections are grouped in at least two groups and the control means is configured to supply power to one electrified enclosure section within a group following removal of power from another electrified enclosure section within the same or a different group.

[0040] Optionally, the at least one electrified enclosure section com-prises one or more first conductors having a first polarity. Optionally at least one second separate conductor(s) (optionally externally located with respect to the enclosure) is provided having a second polarity (opposite to the first).
Thus, in use, an electric field may exist between one or more conductors in an electrified net section and one or more separate second conductor(s). For example, where each side of an enclosure comprises an electrified enclosure section, an associated separate second conductor may be provided outside the enclosure in the vicinity of that side of the enclosure, the electric field formed, in use, lying between the one or more first conductors of the electri-fied enclosure section and the second conductor in other words outside of the enclosure (and thus somewhat remote from the fish inside the enclosure).

[0041] Optionally, at least two or more conductors are provided and the conductors are arranged in pairs, each pair comprising a first and a second conductor, e.g. within an electrified net section, and an electric field is formed between each pair, each conductor in a pair having a different polarity. Optionally, the polarity is reversed periodically.

[0042] Optionally, the polarity of the first and second conductor(s) (e.g.
the first conductor(s)) within an electrified enclosure section and a separate second conductor, or first and second conductors in a pair within an electri-fied enclosure section) are reversed from time to time e.g. periodically.
Optionally the polarity is reversed for each pulse or sequence of pulses.

[0043] Optionally, the system is configured so that current flows through a conductor in an electrified enclosure section, the electric field thus formed being located about that conductor.

[0044] Optionally, power is provided to an electrified enclosure section following triggering. Optionally power is supplied for a predetermined period of time. Optionally, power is supplied intermittently to one or more electrified enclosure sections. Optionally, within a period of power delivery to an electrified enclosure section, power is supplied in pulses. Optionally, the pulse lengths are100 to 15000 or 2000 to 10000 or 10000 and/or the pulse voltage is 6 to 42V or 24 to 36V or 30V and/or the root mean square voltage is between 2mV to 8mV or between 3mV to 6mV or is 3mV.
Optionally, the frequency of the pulses is 5 to 500Hz or 50 to 100Hz or about 10Hz

[0045] Optionally, power is provided in a predetermined sequence of one or more pulses during a period of power delivery to an electrified enclosure section.

[0046] Optionally, the predetermined sequence of one or more pulses is applied to a first pair of conductors in an electrified enclosure section then to a further pair of conductors in the same electrified enclosure section.

[0047] Optionally, there are two or more pairs of conductors and power is applied to two or more or each pair sequentially within the electrified enclosure section.

[0048] Optionally, one or more or each pair of conductors comprises a conductor that also forms part of another pair of conductors.

[0049] Optionally, the conductors of one or more or each pair of conductors do not form part of another pair of conductors.

[0050] Optionally, the area lying bounded by one or more or each pair of conductors overlaps with the area bounded by one or more pairs of other conductors.

[0051] Optionally, a period of power delivery may be is or _.5s or 10s, 20s or 0.5s to 20s or 0.5 to lOs or 1 to 10s. In some example embodiments the period of power delivery may be the same as the pulse length, although it is preferred that the period of power delivery is of the order of seconds and the pulses are of the order of ms in length.

[0052] Optionally, power is pulsed around the electrified enclosure section (which may form the entire enclosure or the entire sides and base of an enclosure) within a predetermined period of time so that within that predetermined period of time each conductor is powered at least once. The predetermined period of time may be 1 to 20s or preferably 1 to 10 s or preferably 1 to 5s long or is or or ._10s or 2.0s.

[0053] Optionally, one or more electrified enclosure sections are two or three dimensional.

[0054] Optionally, at least one trigger device is configured to detect motion of fish to generate an alarm signal and/or at least one trigger device is configured to detect a predator to generate an alarm signal. Optionally, at least one trigger device comprises a sonar trigger device having at least a sonar receiver for receiving sonar signals indicative of the presence and/or motion of a predator. Optionally, the sonar trigger device comprises an integrated sonar emitter. Optionally, at least one sonar emitter, separate from the sonar trigger device, is provided, the sonar trigger device compris-ing a sonar receiver.

[0055] Optionally, at least one trigger device is configured to generate an alarm signal upon at least one predetermined condition state being acti-vated. Optionally, at least one predetermined condition state comprises one or more of: level of fish motion detected; size of a passing object; direction of movement of a passing object; speed of movement of a passing object.

[0056] Optionally, a single electrified enclosure section is provided which forms substantially all the sides, or substantially all the sides and base, of an enclosure.

[0057] Optionally the method comprises: controlling delivery of power to the at least one electrified enclosure section and supplying power to one or more pre-selected conductor(s) in the electrified enclosure section following removal of power from one or more preceding pre-selected conductor(s) in the same electrified enclosure section.

[0058] Optionally the method comprises: controlling delivery of power to two or more electrified enclosure sections; and supplying power to one or more pre-selected electrified enclosure section(s) following removal of power from one or more pre-selected preceding electrified enclosure section(s).

[0059] Optionally the method comprises using any of the features as described herein.

[0060] In a further aspect of the present invention there is provided a predator deterrent system for scaring predators of farmed fish housed in submerged fish enclosures, the system comprising; at least one trigger device configured to detect a predator in the vicinity of a fish enclosure, and config-ured to generate a signal responsive to the detection of the predator; and an alarm device responsive to the signal generated by at least one trigger device, the alarm being configured to generate an alarm adapted to deter fish preda-tors from the vicinity of the fish enclosure; wherein the system comprises at least two alarm devices arranged to emit different respective alarm signals upon activation of the alarm in response to the signal from the trigger device and in which the at least two alarm devices are capable of operating simulta-neously. Optionally, the at least two alarm devices are configured to operate simultaneously upon activation of an alarm device.

[0061] Typically the trigger device is configured to detect threat-related behaviour in the fish or the presence or movement of a predator, and can optionally incorporate a motion detector, typically arranged to detect subsurface motion, either of the fish or of a predator.

[0062] According to one example embodiment, at least one trigger device is located inside the fish enclosure, and is arranged to detect the movement of fish within the enclosure. In certain optional embodiments of the invention, at least one trigger device can be arranged outside the fish enclosure, and can be configured to detect motion of predators outside the fish enclosure.

[0063] In certain optional embodiments, more than one trigger device is provided, for example one or more external trigger devices can be provided for detecting the approach or presence of external predators, and one or more second trigger device can be provided inside the enclosure adapted to detect the motion or other behaviour of fish inside the enclosure, for example to detect increased agitation of the fish and increased speed of movement in response to the approach of a predator. Typically, activation of any one of the trigger devices may trigger activation of one or more of the different alarm systems.

[0064] Optionally, one or more or each trigger device is calibrated to avoid triggering alarms in response to low-level motion of the fish or of non-predatory external marine animals or inanimate objects such as boats, so as to avoid triggering the alarm in response to false signals. Therefore, typically, preferably the trigger devices only trigger(s) a signal to activate alarm device(s) in response to motion (either of the fish or of external predators) above a predetermined calibrated level.

[0065] In optional embodiments, at least one trigger device can com-prise a piezo-electric transducer, or a similar transducer adapted to convert pressure pulses transmitted through the water and initiated by movement of the fish within the enclosure or by movements of predators outside the enclosure into electronic signals for onward transmission through the system.
Optionally, the system comprises an amplifier adapted to amplify signals generated by the trigger devices. Optionally, the amplifier can be incorpo-rated in a trigger device casing, or in other embodiments, is located on a surface control circuit, but in certain embodiments of the invention, the electronics can be housed in a waterproof box that can be submerged and disposed close to a trigger device. Optionally, a trigger device control circuit incorporates a transducer, optionally a power amplifier and optionally a microcontroller.

[0066] Optionally, the signals generated by one or more trigger devices (which are typically amplified by the power amplifier) are transmitted to one or more alarm devices by wireless means. Optionally, the signals are transmitted as radio-frequency signals, or as acoustic signals. In one embodi-ment, the impacts and vibrations picked up by at least one trigger device are interpreted by a control circuit within the trigger device which is programmed to react to send an acoustic signal (e.g. generated using a transponder) through the water to a scramming transducer on an alarm device, or to at least one further trigger device. Optionally, at least one further trigger device is configured to send an acoustic signal (e.g. generated using a transponder) through the water to an alarm device. Optionally, the alarm device is triggered by receipt of the acoustic signal to issue an alarm scram.
Optionally, the alarm device sends an electric signal indicative of the received acoustic signal up the cable to the surface electronics.

[0067] In certain embodiments, the control circuit incorporates a radio-frequency generator or an acoustic signal generator. In such embodi-ments, one or more alarm devices can be triggered by a control circuit that can optionally incorporate a detector for the RF or acoustic signals generated by the trigger device control circuit. In certain embodiments, the signal transmission need not be wireless, and there can be a physical connection e.g.

by means of a cable, or other suitable transmission conduit to transmit the signal from the trigger device to an alarm device.

[0068] Typically, at least one alarm device may comprise at least one acoustic alarm device adapted to emit sound energy in response to a signal from the trigger device. In various example embodiments of various aspects of the invention, the alarm device may comprise a gas discharge alarm device adapted to emit gas in response to a signal from the trigger device, or a power discharge alarm device adapted to discharge electrical power, e.g. in the form of an electric voltage or current into the vicinity of the enclosure (such as an electric net having an electrified net section).

[0069] Optionally, the acoustic alarm device can be sub-surface acoustic noise generator, such as a loudspeaker, hydrophone, or a gas cannon.
Optionally, the acoustic alarm device can incorporate a surface device adapted to generate acoustic noise at or near the surface, and typically above the surface of the body of water in which the fish enclosure is submerged.

[0070] Typically where a gas discharge alarm device is provided this may comprise a gas bubble generator, which can optionally be arranged along a boundary of the enclosure, for example on a face of the enclosure such as a side or a bottom surface, or on the top surface of the enclosure. Typically, where provided, the gas discharge alarm device comprises a source of pressurised gas, a conduit for transmission of gas (optionally from the surface) to a submerged outlet, so that gas discharged from the outlet forms bubbles under the surface, which float up to the surface. The gas bubble generator may be provided close to a surface, typically on a side wall of the enclosure. Typically the gas bubbles form a functional screen when dis-charged from the submerged outlets as they float upwards from the sub-merged outlet to the surface. In certain embodiments, the gas bubble genera-tor may have outlets terminating in a lower face of the fish enclosure for example on the lower face of a net or other enclosure. Optionally, the gas bubble generator may comprise a network of conduits which are optionally interconnected, and can be typically aligned with a grid structure of the enclosure, for example in alignment with the warp and/or weft of a net, and in certain optional embodiments can be secured to the strands of the net, in order to provide additional structural integrity to the bubble generator conduit and to the net. Activation of the bubble screen by sudden discharge of gas bubbles through the submerged outlets typically causes the fish inside the enclosure to move away from the affected surfaces of the enclosure. Option-ally, the bubbles can also have the effect of startling or disrupting the ap-proach of a predator outside the enclosure.

[0071] Optionally, the power discharge alarm device may comprise an AC or DC (or AC and DC) power supply configured to deliver pulses of electrical voltage or current through a cable for transmission through and/or to a portion of the fish enclosure (e.g. a portion of the net at one part of the enclosure) which is optionally located at the bottom of the enclosure. The section of net connected to the cable may contain electrical conductors such as bare wires connected to the cable and interwoven into the warp strands of the net. Each cable may feed a certain area of net with current, and different areas of the net may be fed through different respective cables.

[0072] In one or more embodiments of one or more aspects of the invention, where provided, the power discharge alarm device selects different cables (optionally randomly), and thus different areas of the net for electrifi-cation in response to signals from the motion detector. The selection (option-ally randomly) of different areas of net helps in the preservation of the power supply, which can optionally be batteries. In certain embodiments of the invention, larger sections of the net, or the whole of the net can be electrified at the same time. Random selection of specific areas of the net is optional.

[0073] Optionally, at least one of the acoustic alarm devices is located above the surface of the water in which the fish enclosure is submerged, and can optionally be powered by a gas discharge device, e.g. by a compressor on the discharge device. The compressor can be configured to discharge pressurised air at intervals through a vent or a loudspeaker device. Option-ally, the loudspeaker device can be configured to emit suitable acoustic deterrent noises to deter the likely predators prevailing in the vicinity of the fish enclosure, for example a surface alarm device of this type could in certain embodiments comprise a loudspeaker horn (either electronic or passive) which is adapted to emit bird of prey noises adapted to deter the aerial predators of the fish.

[0074] Optionally, the signals from the control circuit can be transmitted by different ways to different alarm devices. For example, a first surface control box may transmit an alarm signal to a submerged alarm device such as an acoustic alarm by an electric cable, which can run between the first surface control box and the submerged acoustic alarm device. At the same time, a separate alarm signal can be sent from the first surface control box through wired or wireless transmission (such as by radio frequency transmis-sion or similar) to a surface acoustic alarm device, (which can typically be adapted to emit an alarm signal that has a different characteristic to the submerged acoustic alarm device) and/or to a surface control box of a different submerged alarm device.

[0075] Triggering of multiple alarm devices in response to the same trigger signal optionally at the same or substantially at the same time from at least one motion detector trigger device increases the efficacy of deterrent against sea mammals, especially those predators with defective hearing. The different modes of alarm, such as acoustic noise, bubble screens, electrifica-tion etc reduce the likelihood of a particular predator returning to the cage as well as increasing the efficacy of initial deterrents. Optionally, two or more or all of the available alarm devices in the system are simultaneously trig-gered to emit alarms at the same time, but in certain embodiments of the invention, it is sufficient for at least one of the alarm devices to be triggered.
Satisfactory embodiments can be constructed in which subsets of the available alarms are triggered by the same trigger signal, without all of the available alarms being activated. For example, one, two or more sub-surface alarms could be activated without activating any surface alarms.

[0076] In example embodiments, the invention provides a predator deterrent system to protect fish stocks from predator attack, from the water and/or from the air. Embodiments of the system incorporate at least one trigger device adapted to trigger at least one or at least two or several alarm devices, such as an underwater acoustic alarm (such as an underwater acoustic transducer) a bubble screen, an electric net, a gas cannon and an acoustic noise generator such as a loudspeaker on the surface of the fish enclosure. The complete system can more effectively protect fish stocks from aerial attack from birds and sea attack from marine mammals, including those with sensory impairment, such as deafness.

[0077] At least one trigger device typically comprises a motion detector which can be suspended from a line within the enclosure, for detecting the motion of fish in its vicinity, whereas at least one alarm device responsive to the output of the trigger device is optionally located outside the enclosure, or on its outer surface. Typically the system is configured to trigger at least one alarm device above a predetermined trigger signal level from at least one trigger device.

[0078] When either birds or marine mammals attack fish stocks, the fish become agitated which is detected by the trigger device. The trigger device may detect motion of the fish and may comprise a piezo-electric transducer, (to detect the impact of fish on the trigger device) and optionally an ampli-fier, a microcontroller and a power amplifier (so that it can transmit the trigger signal e.g. wirelessly and/or optionally a transducer forming a loud-speaker (so it can transmit the 'trigger signal' via sound - typically a low level 'bleep, bleep, bleep'). The output from the amplifier is typically fed to the transducer which optionally emits the trigger signals, which could be wirelessly transmitted, (e.g. for low energy sounds). Alternatively, or in addition, there may be a physical hard wired connector from the trigger device to an alarm device. At least one alarm device includes a detector (e.g.
a sound transducer) configured to pick up this sound 'trigger alarm signal'.
This detector may be formed separately or integral with the alarm device. A
conditioning signal (e.g. a single tone from the transducer in the underwater acoustic alarm device) may, in combination with other deterrent alarms e.g.
electric net, provide a conditioning stimulus to oncoming predators to elicit a conditioned response to avoid the area in future when they hear this sound.
In certain embodiments, the trigger device sends an acoustic signal typically in the form of a pulse of a particular frequency, which is picked up by a receiver typically on an alarm device linked (usually hardwired) to the surface control box. The receiver may optionally be the acoustic transducer that forms the alarm device and emits the alarm, which is typically connected to the surface control box by a cable. The surface control box typically responds by sending alarm signals (e.g. wirelessly by radio or otherwise) to one or more alarm devices (for example electric net preferably having one or more electrified net sections, compressor, one or more acoustic alarms, gas cannon - all of them or a subset thereof) which activates one or more of them optionally simultaneously.

[0079] One or more acoustic alarms may initiate a triggered (noise) scram response in its underwater transducer to send out a noisy scram.
Optionally, a simplified signal is simultaneously channelled to a radio trans-mitter which sends a signal (optionally encoded) at a designated frequency, to a radio receiver in a secondary surface electronics box. When the radio receiver in this secondary surface control box receives the (encoded) signal it may activate one or more of an air compressor, an electrified net (e.g. one or more electrified net sections), the surface speaker and any additional alarm devices connected to the secondary unit. The signal may be transmitted to a third or further surface control box which may control one or more alarm devices.

[0080] The surface control box may contain a control circuit configured to assess whether the signals detected by at least one trigger device represent a seal attack, and if so, it is adapted to trigger, at least one alarm device e.g.
an acoustic noisy scram alarm device.

[0081] To operate a bubble net alarm, the alarm signal may also trigger an alarm signal from the surface control box which is sent (e.g. via an in-built radio transmitter in a surface control box) to a bubble net alarm comprising a receiver connected to a solenoid actuated valve which releases air from a compressor through a pipe to a submerged bubbler device which discharges streams of air bubbles up through the enclosure containing the fish. The sudden release of streams of bubbles within the enclosure typically causes the fish to move away from the edges of the net and consequently from the predator.

[0082] To operate a power discharge alarm, the alarm signal may activate an AC or DC (or AC and DC) power supply which may deliver electricity though a cable down to a piece of net (an electrified net section) at the bottom of the enclosure which typically has electrodes interwoven into it.
The electricity may be targeted to target different sections of the net at any one time to conserve power. The selection of net section(s) to be electrified may be made randomly, or in response to a trigger signal from a local trigger device adjacent to that net section or in accordance with a predefined se-quence or randomly. The electricity may be 'pulsed' from net section to net section (optionally at random) switching on one section as another is switched off to conserve power. Alternatively or in addition, within one or more electrified net section, the electricity may be applied in pulses of a certain length, voltage and frequency e.g. 10 to 1500 kts, or more preferably 200 to 1000 kts, DC voltage at 6 to 42V or more preferably 24 to 36V, at a pulse frequency of 5 to1-500Hz, more preferably 50 to 100Hz. As an example, pulses of 24V of 2000 length at a frequency of 50Hz or 100Hz may be provided, or pulses of 36V of 1000 length at a frequency of 50 Hz or 100Hz may be provided. Other variations of these pulse parameters may be envis-aged by someone skilled in the art from the disclosure herein. The pulse parameters may be varied and/or variable during operation to suit a particular enclosure site and local conditions. A period of power delivery may be 0.5 to 20s, more preferably 1 to lOs long. A predetermined period of time, during which all conductors within an electrified net section may be powered at least once, may be 0.5 to 20s, or more preferably 1 to lOs long.

[0083] A gas discharge device is provided this may incorporate a compressor and/or a surface loudspeaker for discharging noisy shots of air through a surface loudspeaker and may be configured for playing bird of prey noises.

[0084] Using the radio transmitter frequency or wired connections, part or all of the apparatus can be triggered manually and/or on an automatic timed basis using a laptop and software e.g. a frequency timer algorithm in the control box to send timed signals to one or more alarm devices.

[0085] Optionally it is advantageous to activate subsets of the available alarms, rather than setting off all alarms (optionally simultaneously) upon every predator encounter. Optionally the system can be remotely configured to activate all alarms in response to predator detection, or to vary the combi-nations of any one or more alarms. The selection of which subset of alarms to activate upon predator detection may be switchable remotely. For exam-ple, the system may be set up to respond acoustically and with electrification of one or more net sections (or the entire net) for a set time. The same response from the system with each predator attack may eventually induce habituation, but ideally before that stage was reached, the system could be switched (optionally locally or remotely) to reconfigure the subset of one or more alarms that were activated, so as to activate the e.g. an acoustic alarm and electric net etc. in response to predator attack. This provides more ways to surprise the predator and avoid habituation to any one form of deterrent.
Optionally, the system can have a timer device, and can be configured to change the subset of alarms (or the operation of any particular alarm e.g.
choice of electrification sequence, choice of scram sequence) that are acti-vated by a given trigger after a period of time, in order to reduce the likeli-hood of habituation.

[0086] The system is typically able to reduce the likelihood of habitua-tion to the sound being generated by limiting exposure so that an alarm signal is only generated when a predator attacks. Where a bubble screen alarm device is used, this causes the fish to move away from the edges of the enclosure, and may also be positioned to force fish downwards from the surface of the enclosure in the event of aerial attack. Where an electric net alarm device is used, electrodes incorporated into one or more sections of the enclosure (e.g. near the base) can serve to further deter persistent and deaf seals and other predators, by providing (e.g. random) electric fields at intervals along the netting. By seeking to deter the predator using more than one modality (preferably including at least an electric net in conjunction with a conditioning signal such as a single plain tone from an acoustic alarm device) the likelihood of a predator returning to the cage is greatly reduced.

[0087] In alternative embodiments, at least one trigger device is config-ured to detect the presence (and optionally the movement) not of the fish inside the enclosure, but of larger marine mammals outside the enclosure. At least one (optionally external) trigger device is typically configured to interact with at least one alarm device in a similar manner to an internal fish motion detection trigger device. An alternative predator detector trigger device typically uses either sonar, heat or a movement (plasma) sensor. It may be located on the outside of the enclosure or may be hung from a buoy, which can optionally also be used to suspend other alarm equipment, including one or more acoustic alarm devices such as hydrophones. Where a sonar trigger device is provided, a sonar signal can either be generated by an existing hydrophone or by a separate sonar signal generator (such as a further hydrophone) optionally having a power amplifier and optionally a transducer.
In certain circumstances, the distance of the predator from the enclosure can be measured by using several sonar signal generators, and by measuring of the echo to each one. The system can optionally incorporate signal process-ing devices which can be configured to determine if incoming signals from the triggers are ambient noise that should not trigger an alarm signal, or an indication of a predator. Optionally, the system can be configured to deter-mine the direction of motion and/or speed of the predator. An algorithm may be used to determine if the object is the size of a predator and/or if the predator is moving away or passing a cage and/or approaching a cage and/or its speed. If it is determined a predator is incoming, the system can be configured to activate one or more alarms, for example by emitting a low energy signal such as a low energy sound (as with the fish trigger device), which will set off the complete alarm system as described above.

[0088] The system may convert a signal triggered by a trigger device or from an activated alarm into a signal that can be relied on to initiate an array of different equipment, positioned typically at different locations around a fish farm. The trigger devices within or without the net, located underwater, may have no physical connection to alarm devices such as the electrified net, the bubble screen, the speaker system or any additional deterrents. There-fore, an alarm signal received by a surface control box may need to be interpreted and translated into a simplified signal that is transmitted to and received by one or more alarm devices and activates one or more external switches to initiate one or- more additional alarms. Optionally these are triggered in a timed response, which can optionally be configured to switch a subset of one or more alarms that are activated in response to the trigger signal. Optionally the timer device can be incorporated into the surface control box circuitry.

[0089] Optionally, simple embodiments of the system can be hard wired entirely, so that signals carried between one or more trigger devices, one or more control boxes, and one or more alarm devices can all be carried by cables etc. The system may incorporate relay outputs and inputs to signal various independent or interconnected elements such as deterrent devices (e.g. one could be used to directly start a compressor, electric net or external speaker). The system (and in particular the surface electronics may comprise radio transmitter/receiver and/or WIFI capability to communicate with the various elements.

[0090] In certain embodiments in which at least one predator detection trigger device(s) adapted to detect the presence of fish predators outside the enclosure (instead of fish movement within the enclosure the trigger devices) can be located outside the fish enclosure but may be adapted to trigger the same response as the embodiments described with respect to the fish mo-tion-sensing trigger device in other words, a low noise acoustic alarm signal ('bleep, bleep'). The predator trigger device can optionally use one or more sonar detectors, heat detectors or movement detectors.

[0091] Optionally, the predator detection trigger device can be located on the outside of the fish enclosure, for example suspended on the external surface of an enclosure net, or can be suspended from a separate flotation device such as a buoy. Optionally one or more alarm devices can similarly be suspended from external buoys outside of the fish enclosure, and option-ally the trigger device and alarm devices can be suspended from the same or from different buoys. In the case of a sonar predator detection trigger device, the trigger device may comprise a sonar receiver, and optionally a sonar transmitter. Alternatively a sonar signal may be generated by an external alarm device in the form of a transducer (to emit sound), which may also generate the alarm in response to a signal from the sonar receiver. In other embodiments, a sonar signal (e.g. a ping) can be generated by a separate signal generator, for example one or more sonar transmitters located within the sonar trigger device and/or within one or more alarms and/or within one or more trigger devices. Optionally, in certain embodiments, the returns from the sonar receiver can enable distance measurement between the predator and the sonar sensor, and/or triangulation of the location of the predator by employing several transducers (to emit sound) and several sonar receivers (e.g. the transducer(s) - to receive sound - or hydrophones).
Therefore, in certain more sophisticated embodiments of the invention, the sensor can optionally detect not only that a predator is in the same vicinity as the fish enclosure, but also the location of the predator, and whether the predator is moving towards or away from the fish enclosure.

[0092] Any feature of any embodiment of any aspect of the invention may be combined with any feature of any other embodiment of the same or any other aspect of the invention, unless the context dictates otherwise.

[0093] All numerical values in this disclosure are understood as being within the standard variation expected in practice for parameters of that kind.
Brief Description of the Invention

[0094] The invention will now be described with reference to the following Figures, by way of example only, in which like reference numerals refer to like features.

[0095] Figure 1 shows a schematic perspective view of a submerged fish enclosure with various triggering devices according to an example embodi-ment of the invention.

[0096] Figure 2 shows a schematic plan view of a fish farm with multiple fish enclosures 10 associated trigger devices 28 and centrally located medium frequency acoustic alarm 30, for use in various embodiments of the invention.

[0097] Figure 3 shows a schematic elevation view of a fish farm similar to that of Figure 2, with fewer enclosures for use in various embodiments of the invention.

[0098] Figure 4 shows a schematic side elevation view of a submerged fish enclosure having a fish motion detector trigger device 28 for use in various embodiments of the invention.

[0099] Figure 5 shows a schematic side elevation view of a submerged fish enclosure having a number of electrified enclosure sections (here electri-fied net sections) according to a first aspect of the invention.

[0100] Figure 6 shows a schematic side elevation view of a fish enclo-sure and predator deterrent system according to a further embodiment of the invention.

[0101] Figure 7 shows a schematic view of a modular predator deterrent system according to one aspect of the invention and a schematic perspective view of a submerged fish enclosure for use therewith.

[0102] Figure 8 shows a schematic perspective view of a submerged fish enclosure having a predator deterrent system according to a further aspect of the invention or according to a further embodiment of the first aspect of the invention.

[0103] Figure 9 shows a schematic perspective view of a submerged fish enclosure according to a further embodiment of a further aspect of the invention or a further embodiment of the first aspect of the invention.

[0104] Figures 10A to 10E show various example switching arrange-ments for first and second conductors for an electrified net section according to the invention.

[0105] Figures 11A to 11C show various arrangements for pairs of first and second conductors within an electrified net section.

[0106] Figure 12A to 12C show various arrangements of pulses and sequences of pulses within a period of power delivery to an electrified net section, applied to pairs of first and second conductors (such as those in Figure 11A to 11C) within an electrified net section.

[0107] Figures 13A to 13C show alternative arrangements of conductor pairs, with optional floating conductors in between electrode pairs.

[0108] Figure 14 shows a schematic overview of example architecture that may be used to provide an electric net for a submerged enclosure and an electric net control system having a surface control box component and a sub-surface outstation component.

[0109] Figure 15 shows a schematic diagram of example logic for a sub-surface outstation such as that shown in Figure 14.

[0110] Figure 16 shows a sequence of activities that may be carried out over time in a sub-surface outstation controlling ten conductors (or ten pairs of conductor), with, for example, communication between adjacent outsta-tions by sensing voltage leakage from a previous outstation. This facilitates transfer of electricity from one set of conductors powered by single sub-surface outstation to a neighbouring set of conductors powered by a neighbouring outstation, sequentially.
Detailed Description of the Invention

[0111] Referring now to the drawings, a predator deterrent system 1 for deterring predators in the vicinity of a fish enclosure provides an enclosure in the typical form of a submerged net or cage 20 containing a population of farmed fish or other aquatic livestock. The enclosure 10 (here provided by a net 20) typically has near vertical sides and a curved base (and optionally a roof - not shown) and encloses the fish, forming a barrier between the fish inside the enclosure 10, and external marine predators such as seals, or aerial predators such as birds. In the preceding and following description, the term 'net' (meaning a permeable, flexible structure) will be used for simplicity.
It will be understood that a 'cage' (meaning a permeable, inflexible structure) or alternative permeable structures could be used as an alternative to a net to form an enclosure, and the term 'net' is used in the following description as an example only of all such structures, and is to be interpreted accordingly unless the context dictates otherwise.

[0112] Figure 1 shows various components of a predator deterrent system according to the invention. In particular, Figure 1 shows a fish enclosure 10 comprising a net 20, a floating frame 22 for incorporating a walkway (not shown), horizontal ropes 24 suspending lightweight lines 26 on each of which two motion detector trigger devices 28 are located floating within net 20. One or more trigger devices 28 may be used. Motion detector trigger devices 28 are configured to emit an acoustic signal upon one or more impacts of sufficient intensity from fish within the enclosure 10. For this purpose trigger devices 28 may comprise a motion detecting transducer (not shown). Furthermore, trigger devices 28 may comprise a transponder for emitting a low level noise (see acoustic alarm signal 48 in Figure 7) such as a low level 'bleep, bleep, bleep'. Thus, upon agitation of the fish of a prede-termined level, one or more trigger devices 28 activate an alarm signal such as acoustic alarm signal 48 (see Figure 7). Alternatively, or in addition, one or more sonar trigger devices 70 may be provided outside enclosure 10.

[0113] A sonar trigger device 70 may comprise a simple transducer emitting a sound and receiving a reply to identify range (echo), speed (Dopp-ler), and/or size (amplitude) of the object. In this example embodiment, a transducer within the sonar trigger device 70 emits sound at around 400kHz.
The sonar transducer may be directional and have coverage of around 120o and may be able to listen up to a range of 50-100 metres or may be omni-directional looking out over 3600. The Doppler shift allows the device to spot familiar targets by recording echo (time), Doppler (speed) and amplitude (size). The transducer may be fitted under water at a depth of around 1 to 5 metres from the surface beside the fish farm cages. It may look out over 120o and sufficient quantities of sonar trigger devices 70 may be required to provide for coverage of a fish farm site. The sonar trigger device 70 is preferably connected to a surface box 32 (in Figure 7) for supplying power to and giving/receiving data to/from the transducer. In a predator deterrent system according to the invention one or more trigger devices 28 and/or one or more sonar trigger devices 70 may be provided. In one aspect of the invention, trigger devices are not required. In a further aspect of the invention multiple trigger devices and/or multiple alarm devices are provided.

[0114] Figures 2 and 3 show schematic plan and side elevation views of a fish farm, having twelve and two fish enclosures 10 respectively. In the fish farms of Figure 2 and 3, each enclosure 10 is provided with a single trigger device 28 mounted on a rope 24 and suspended in the water within the perimeter of the net 20 forming enclosure 10. A first underwater alarm, in the form of a medium frequency acoustic alarm device 30, is provided suspended by a rope having a power cable 34 and signal connections 36 facilitating connection between medium frequency acoustic alarm device 30 and a first surface control box 32. Typically, a medium frequency acoustic alarm device 30 is situated around one metre below the base of the fish enclosures 10 and typically centrally within the fish farm within around fifty metres of the perimeter of the fish farm.

[0115] Referring now to Figure 4, alternatively, or preferably in addition to a medium frequency acoustic alarm device 30, a low frequency acoustic alarm device 50 may be provided either powered and/or controlled via a similar (or identical or the same) first surface control box 32 or its own separate control box 232 (see Figure 7). Typically, a medium frequency acoustic alarm device 30 will operate in the range 10-20kHz and a low frequency acoustic alarm device will operate in the range 2-7kHz, or more preferably 2-5kHz.

[0116] The surface box 32 (232) feeds power and determines the algorithm for the sound varieties to be emitted from the low frequency acoustic alarm device 50. A trigger device 28 is provided in the pen with the fish 44 within net 20. The fish behaviour activates (fish motion detector) trigger device 28, typically by a number of impacts from the fish within a pre-set time frame, causing an acoustic alarm signal to be issued. This may be in the form of a low level 'bleep, bleep' sound (see 48 in Figure 7).
Either or both medium frequency acoustic alarm device 30 and/or low frequency acoustic alarm device 50 may be triggered upon receipt of the acoustic signal from the trigger device 28 depending upon the individual threshold set within each alarm and/or activation of one alarm may result in activation of another alarm (e.g. via control signals). Thus, these alarms may operate substantially simultaneously or in sequence one after the other as fish behaviour becomes more agitated. Control systems may be provided for operating one or both alarms simultaneously or in sequence after a first alarm is triggered or in a series of sequences. Within a medium frequency acoustic alarm device 30, the transducer is centred around 16kHz (e.g. between the range 10-20kHz). Within a low frequency acoustic alarm device 50 the transducer provided is centred around 3kHz (within the range 2-5kHz) which is within the sensitive hearing range of seals but not porpoises. The alarm issued by either the medium frequency acoustic alarm device 30 or the low frequency acoustic alarm device 30 may typically take the form of a scram comprising multiple frequencies within the range issued at various points within a cycle of sound. These frequencies may be randomly selected within the range.

[0117] Thus, in one aspect the invention provides a predator deterrent system comprising one or more trigger devices 28 and multiple acoustic alarms. Optionally, the acoustic alarms may both be situated within the same housing.

[0118] Turning now to Figure 5, a preferred aspect of the invention is shown in which a predator deterrent system 1 is provided comprising an electrified enclosure 10 having a net 20 provided with electrified enclosure sections 40A, 40B, 40C, 40D, 40E, 40F, 40G and 40H. Each of these individual electrified enclosure sections 40A to 40H are connected by a separate cable to electric net surface control box 132. Electric net surface control box 132 may comprise an AC generator, and/or a pulse DC generator unit as well as control electronics for controlling the timing and triggering of =
power delivered to each electrified section 40A to 40H. In the following description each electrified enclosure section 40A to 40H will be described as an electrified net section. It is to be understood that the following description equally applies to an electrified cage having electrified cage sections as well as to other types of enclosure having electrified enclosure sections.

[0119] Individual cables 42 may connect each electrified net section to 4011 to electric net control box 132. Typically these cables are insulated and are interwoven into the netting with stainless steel filaments. Within each electrified net section 40A to 40H, conductors (typically wires)are interwoven into the netting. Each electrified net section 40A to 40H may comprise one conductor or may comprise a plurality of conductors. The conductors within each electrified net section 40A to 40H may be provided in an array of conductors. The conductors may be arranged in pairs (see Figures 11A to 11C). Where multiple trigger devices are provided within a single enclosure, the location of these trigger devices may be passed to the electrified net control box 132 to enable one or more electrified net sections adjacent one or more pre-selected and/or recently triggered trigger device 28 to be provided with power, either continuously, or for a period of time.

[0120] It is to be understood that where power is delivered to an electri-fied net section over a period of time, this power may in itself be 'pulsed' during that period of power delivery for example for 0.5-15000, 100 to 1500o, 2000 to 10001.6, preferably 1000 ,s (within expected tolerances) at a voltage of 6 to 42 V, more preferably at 24 to 26V, preferably at 30V (within expected tolerances), at a frequency of 5 to 500Hz, or more preferably 50 to 100Hz, 10 to 50Hz, more preferably 10Hz (within expected tolerances) and/or may be 'pulsed' to provide the period of power delivery. Thus, a sequence of pulses (for example as described above) may be provided to one or more electrified net sections 40A to 40H during a period of power delivery and that period of power delivery might extend from a few fractions of a second to several seconds or even minutes. Preferably the period of power delivery is 1 to 2 seconds, more preferably 1 second. Preferably, this period of power delivery is repeated to that net section every few seconds, for example every 2 to 6 seconds or preferably every 4 to 5 seconds. Alterna-tively and/or in addition, power may be delivered in pulses to one section then another in pulse lengths of a .is to a few p,s to a few ms or even a few hundreds of ms or few seconds Furthermore, a sequence of pulses may be repeated during a period of power delivery. Thus, the period of power delivery may be described in one sense as a "pulse" of power (being on for a period of time and off for a period of time) and within a period of power delivery, power may be delivered in "pulses" for example in a sequence of on/off pulses within a period of power delivery, thus the period of power delivery may form an envelope of on/off power delivery overlaying a se-quence of pulses delivered to the conductor(s) within an electrified net section.

[0121] The period of power delivery to an electrified net section may be selected to provide sufficient time for the predator such as seal 46 to be deterred from approaching that region of the net. Similarly, within a period of power delivery, the sequence of pulses, and/or the waveform and/or voltage and/or frequency of pulses within that period of power delivery, may be selected to promote avoidance of the area by a predator. For example, if a predator is known to return to a particular section of the net each day, the period of delivery may be time to coincide with the expected return of the predator and/or the period of delivery may be extended to cover the expected return time and/or the nature of the power delivered (pulse width, pulse height, pulse frequency and voltage) may be increased from one period of power delivery to the next until the predator is discouraged from returning (noted for example by the lack of triggering of a trigger device during that expected return period of the predator).

[0122] Power consumption can be reduced as follows: by providing a triggered electric net that is only powered (and preferably then only powered for a limited period of time) upon receipt of an alarm signal and/or by providing a one or more electrified net sections (e.g. 40A to 40H) that are powered intermittently e.g. in pulses. One or more electrified net sections 40A to 40H may be powered separately or together in a pre-determined sequence or randomly to limit the amount of power required at a particular point in time or during a particular period of power delivery. Power may be delivered to neighbouring electrified net sections e.g. sequentially. For example, power may first be delivered to section 40A then, upon removal of power from 40A, it may be delivered to section 40B. Upon removal of power delivery from section 40B, power may then be delivered to section 40C. Upon removal of power from section 40C, power may be delivered to section 40D and so on.

[0123] The electrified net sections 40A to 40H may be divided into groups each comprising one or more net sections: for example, a first group may comprise 40A, 40C, 40E and 40G and a second group may comprise 40B, 40D, 40F and 40H. Power may be delivered to the first group for a period time. During removal of power from the first group of electrified net sections 40A, 40C, 40E and 40G, power is then delivered to the second group of electrified net sections 40B, 40D, 40F and 4011. Several such groups may be provided each having one or more electrified net sections.
Thus, power is, in one sense, pulsed to alternate sections of the net, reducing overall power requirements. Within one or more electrified net sections a number of conductors may be provided which may alternatively or in addition be similarly pulsed (e.g. during a period of power delivery to that net section) as will be described in more detail in relation to Figure 7 and Figures 12A to 12C.

[0124] Referring now to Figure 6, within enclosure 10, a line 24 typically suspends at least one trigger device 28 in a submerged location, typically within a central part of the enclosure 10, spaced away from the walls. Optionally more than one trigger device 28, 70 can be provided. In certain embodiments of the invention, the trigger device (e.g. 70) need not be inside the enclosure 10, but can be attached to the side walls of the enclosure 10, or optionally can be located outside the enclosure 10. In the current embodiment, at least two trigger devices 28 are suspended on the line 24 within the enclosure 10, and typically each comprises a motion detector adapted to detect changes in the swimming behaviour of the fish 44 within the enclosure 10. Typically the trigger devices 28 incorporate a sensor which can be adapted to sense impacts from fish becoming agitated and knocking into the trigger device 28 creating a direct impact on the trigger device 28.
Alternatively or additionally the sensor can be in the form of a pressure sensor (not shown) arranged on the trigger device 28 adapted to pick up waves of pressure changes within the water in which the enclosure 10 is submerged, without requiring direct impacts by the fish on the trigger device 28 before a trigger signal is triggered. Typically, a signal from the sensor is amplified by an amplifier 75, and may be processed by a signal processor in the typical form of a micro-controller 76 before being fed to a power ampli-fier 77. Optionally the signal from the power amplifier 77 can be transmitted through the line 24, or through a cable carried by the line 24 (not shown), and transmitted to a processing circuit in a surface control box 132. How-ever, in the present embodiment, the devices 28 typically have no direct physical hard wired connection to the remainder of the system, and the output from the power amplifier 77 is relayed to a trigger signal transmission device typically in the form of a piezo-electric transducer 74 on the trigger device 28. The transducer 74 typically emits low energy signals (e.g. acoustic signals such as vibrations) into the water which are transmitted to a receiver 52 (optionally on an alarm device 30) that is submerged in the water outside the enclosure 10. Typically the low energy vibration signal received by the receiver 52 is optionally converted and then transmitted to the surface control box 32 by means of a cable 56, and is processed (either in the surface control box 32 or in electronics associated with the receiver 52, if present, within the alarm device 30) to analyse whether the impact detected by the trigger device 28 represents a true attack by a predator, or is representative of normal moments of the fish inside the enclosure 10, in which case no alarm is generated. In this example embodiment, analysis takes place in surface control box 32. In the event that a predator attack is detected, the surface control box 32 sends an alarm signal to an alarm for example to the acoustic alarm device 30, typically through the cable 56, although alternatively the alarm signal can optionally be sent wirelessly. The acoustic alarm device 30 emits a loud noise to startle or scare marine predators such as seals within the vicinity. Optionally, each trigger device 28 has a timeout feature lasting about 90-120 seconds after activation, during which time they cannot be re-activated, which reduces the chances of continual activation in the event that the majority of the fish just happen to be in that area of the enclosure.
Each trigger device 28 typically has its own serial code, which can optionally be transmitted with the trigger signal, so in certain embodiments, the control box 32 can be configured to determine if one particular trigger device has been responsible for many hits over a time period and can then adjust its response to reduce the alarm activation in response, which reduces false activation of alarms resulting from one particular trigger hitting a side of the enclosure. Further this provides data relating to predator approaches.

[0125] Optionally, at least one sonar trigger devices, such as an omni-directional sonar trigger device may be provided inside the enclosure (net) and configured to observe and analyse behaviour of the fish, whereby fish accumulations at one side of the enclosure may indicate presence of a predator at an opposing side of the enclosure. Whereupon, the sonar trigger device may issue an alarm signal so that for example, an alarm device e.g. an electrified net section in that side of the enclosure may be activated.

[0126] For example, where a powered discharge alarm (such as an electric net device comprising one or more electrified net sections 40) is provided (see Figures 5, 7,8 and 9) activation of a particular trigger device 28 within a net can result in a particular electrified net section being activated (electrified) in that vicinity. Or, for example, where one trigger device 28 is provided per enclosure 10, activation of that trigger device 28 can result in electrification of the net (or cage) of that enclosure. The powering of electri-fied net sections in response to a trigger and/or in a random or pre-determined sequence assists in reducing overall power consumption of the net whilst appearing electrified over part, most or all of that enclosure.

[0127] In this example embodiment, in which a gas discharge alarm device is provided, at the same time as the alarm signal is sent through a cable 56 to the acoustic alarm device 30, to generate an underwater acoustic alarm, the surface control box 32 may relay a second signal to be transmitted either by wireless transmitter 66 (which can be a radio frequency transmitter, or a WIFI transmitter), or through a hard-wired cable 68, to activate a second alarm device for example in the form of a gas discharge alarm device 90.
The gas discharge alarm device 90 typically has a wireless signal receiver 66' to pick up the alarm signal transmitted by the transmitter 66 and to convert that into a signal activating a valve in the gas discharge alarm device to a compressor 92, which reacts by supplying a blast of compressed air or other gas through a conduit 94 to a submerged bubbler 96 located at or near at least one of the side walls of the net. Typically the gas bubbler 96 comprises a ring device having a conduit for the gas, and apertures to emit gas bubbles at spaced apart locations on the ring, and is typically spaced slightly inside the outer wall of the enclosure 10. A bubble screen of rising gas bubbles is emitted from the bubbler 96 on activation of the gas discharge alarm device 90, which causes the fish near the side walls of the enclosure 10 to swim away from the walls into the central region of the enclosure, and away from the external predatory sea mammals such as seals etc. Typically the gas discharge device can incorporate secondary bubblers located at the base of the net 3, and optionally at the surface of the net 5. All of these can typically be coordinated to simultaneously release streams of bubbles at the same time to cause the fish to move away from the edges of the enclosure, and conse-quently away from the predator, whether marine or aerial. The bubbles may also startle and disturb larger marine predators and deter them from ap-proaching the walls of the net, especially when the conduit and apertures have larger bores, and the bubble screen is generated suddenly by the compressor.

[0128] Compressor 92 may also be linked to an air horn 98 or other surface acoustic alarm device, which may be triggered at the same time as the bubbler 96 and can be arranged to transmit either noisy blasts of air to scare off areal predators, or alternatively can be provided with a speaker to pro-duce more specific acoustic signals adapted to scare aerial predators. For example, in the case of the main aerial predator the fish being seagulls, the air horn 98 may be programmed to emit bird of prey noises emulating hawks, eagles etc. to deter the seagulls.

[0129] The alarm signal optionally transmitted to the gas discharge alarm device 90, may alternatively or in addition typically be transmitted to an electric alarm control box 132, which may be connected to the same receiver or hard wired (to another alarm device). The electric alarm control box 132 typically comprises an AC or DC (or AC and DC) power supply linked by a cable 58 to one or more areas of the enclosure 10 which are electrified by the power supply in the electric alarm control box 132. Typi-cally the electric alarm control box 132 delivers pulses of electrical current through the cable 58 to areas of the net, such as electrified net alarm device 40 forming an electrified net section at the base 3 of the net which typically has electrical conduits optionally in the form of conductors interwoven into the mesh of the enclosure. The delivery of electrical power to the electrified net alarm device 40 of the base 3 discourages seals from trying to enter the enclosure at the base section 3, and may also discourage fish from remaining in that area, typically by providing an uncomfortable electric field in the area of the water that unsettles the predator and the fish, thereby separating the fish from the predator.

[0130] The predator deterrent system 1 has the advantage that it can reduce the exposure of predators to alarm stimuli that are triggered when there is little likelihood of attack, thereby reducing the likelihood that the predators will habituate to any one form of alarm signal. The combination of one or more deterrents in one triggered system spans a wider range of sensory modalities allowing the integrated deterrent to be more effective at altering the behaviour of predatory mammals or birds by being responsive to predator's behaviour, and avoids unnecessarily long periods of active alarms which can cause habituation in predators and can shorten the life of any batteries powering the system. Modifications and improvements can be incorporated; for example, the alarm signal generated by each of the alarm devices can be modified in accordance with the signal from the trigger devices, to generate larger or more frequent alarm signals in the event that the system senses that a predator is approaching the fish enclosure, and to moderate or reduce the intensity or frequency of the alarm signals in the event that a system detects that a predator is moving away, so as to reduce the likelihood of habituation of the predator to the alarm signals, and improve responsiveness of the predator to the overall system. According to certain embodiments, a large number of combinations of different alarms can be triggered by single or multiple trigger signal, which can be adjusted to be responsive to the behaviour and degree of persistence of a predator. In certain embodiments, the system can be reconfigured (optionally remotely, and optionally on a timed basis) to respond in different ways with different combinations of the alarms, thereby reducing the chances of habituation.

[0131] Referring now to Figure 7, a modular predator deterrent system 1, according to a further embodiment of the invention is shown comprising various alarm devices and trigger devices and other components which may be included within the modular system. Preferably at least two alarm devices are provided. The modular predator deterrent system in Figure 7 comprises a medium frequency alarm surface control box 32 which here also functions as a master surface control box. The system preferably further comprises an electric net surface control box 132 containing a control circuit (not shown) and a power supply. Electric net surface control box 132 functions as a distribution unit for an electric net alarm device 40. Electric net surface control box 132 functions as a distribution unit providing control signals and power to electric net alarm device 40.

[0132] Medium frequency alarm surface control box 32 provides control signals via a line 56 and optionally power by a line 58 to a submerged medium frequency alarm device 30.

[0133] An optional low frequency alarm surface control box 232 is connected to a submerged low frequency alarm device 50 and provides control signals and optionally power via cables (unlabelled). Optionally a low frequency alarm surface control box may be omitted and instead suitable circuitry provided within master surface control box 32, for providing control signals and optionally power to low frequency alarm device 50 (this arrange-ment is shown in Figure 4).

[0134] Optionally a further alarm surface control box 332 is provided in conjunction with a further alarm device 60 which may be submerged or may be a surface alarm device. Further alarm surface control boxes and alarm devices may be provided as required. Each surface control box is preferably in communication with a master surface control box, such as medium fre-quency alarm surface control box 32, via a wireless link using transmit-ter/receiver 66 or by optional cables 68.

[0135] In the embodiment shown in Figure 7, medium frequency alarm device surface control box 32 is also directly connected via a cable (unlabelled) to a submerged sonar trigger device 70. Sonar trigger device 70 emits and receives sonar signal 72 for detecting submerged objects such as an incoming predator 46A and a receding predator 46B. Submerged medium frequency alarm device 30 is provided with a transducer 52 for receiving acoustic alarm signals from trigger devices 28 and for emitting a medium frequency deterrent sound 54. Also shown in Figure 7 is a low frequency alarm device 50 having a transducer 52' for receiving low level acoustic alarm signals (e.g. from trigger devices 28) and for emitting a deterrent sound 54'.

[0136] Thus, Figure 7 shows a modular predator deterrent system having a number of trigger devices, in this case trigger devices 28 and a sonar trigger device 70, a number of alarm devices, here a medium fre-quency alarm device 30, an electric net alarm device 40, a low frequency alarm device 50, and one or more further alarm devices 60. It will be understood by those skilled in the art that one or more trigger devices 28, 70 may be used and one or more alarm devices 30, 40, 50, 60 may be used.
One or more surface control boxes 32, 132, 232, 332 may also be provided as will be understood by someone skilled in the art. In use, the predator deterrent system 1, Figure 7, works in a similar way to those shown in Figures 1 to 6. When a predator, such as predator 46A, approaches enclo-sure 10 sonar trigger 70 issues sonar signals and receives sonar signals 72 so as to determine the size and motion (direction of motion and/or speed) of predator 46A. A signal is sent, typically via a cable, to master surface control box 32 which may issue control signals sounding an alarm to one or more of the alarm devices 30, 40, 50, 60. For example, control signals may be sent wirelessly via transmitter/receiver 66 to an electric surface control box activating the electric net alarm device 40. Alternatively, or in addition, control signals and optionally power may be provided to one or more of the medium frequency alarm device 30 and for a low frequency alarm device 50.

[0137] Should the sonar trigger 70 have failed to detect the approaching predator 46A, trigger devices 28 located within enclosure 10 may be acti-vated by fish motion upon the approach of a predator and may issue a low level acoustic alarm signal 48. A conditioning signal e.g. such as an arbi-trary single tone) from the alarm device (along with any alarm sounds e.g. a noisy scram form the acoustic alarm device) may be used, preferably simulta-neously with operation of the electric net, to an approaching predator. The low level acoustic alarm signal 48 may be detected by a receiver 52, 52' in one or more alarm devices 30, 50. Upon receipt of these low level acoustic alarm signals 48, alarm devices 30 or 50 may be activated to issue deterrent sounds and/or to pass signals indicative of the triggering of a trigger device to master surface control box 32. Master surface control box 32 may then cause one or more further surface control boxes to activate preferably simulta-neously e.g. electric net alarm device 40. Thus, as will be appreciated by someone skilled in the art, the modular predator deterrent system shown in Figure 7 enables a predator deterrent system to be built up dependent upon the needs of a particular fish farm in a particular location.

[0138] In more detail Figure 7 shows an enclosure 10 for a submerged fish farm comprising a net 20 of generally rectangular cross section having two short sides and four long sides, a base and a roof (not shown). Four separate trigger devices 28 are located within net 20, one adjacent a central portion of each of the four generally vertical sides of net 20. A first electri-fled net section 140A is provided with five vertical electrical conductors 62A, 62B, 62C, 62D and 62E. A second side of net 20 is electrified providing electrified net section 140B having four horizontal conductors 64A, 64B, 64C
and 64D. The remaining sides have been similarly provided with electrified net sections but this is not shown for clarity. The number of conductors and their orientation may be varied without departing from the scope of the invention. A medium frequency acoustic alarm device 30 is located outside the net 20. Medium frequency acoustic alarm device 30 operates in the acoustic range 10-20kHz centred around 16kHz. It is provided with an internal transducer 52 for receiving and emitting sound waves. A second low frequency acoustic alarm device 50 is provided also having a transducer 52' for receiving and emitting sound waves. One or both of the acoustic alarm devices 30/50 may be provided with an internal rechargeable battery to reduce reliance on good electrical connection with the surface, for issuing strong deterrent acoustic alarms.

[0139] Thus, net 20, in view of the provision of electrified net sections 140A, 140B etc. provides an electric net alarm device 40. Electric net alarm device 40 is controlled and preferably provided with power by electric net control box 132. Medium frequency acoustic alarm device 30 is controlled by first surface control box 32, here also optionally designated as a master control box. Low frequency acoustic alarm device 50 is controlled by a low frequency alarm surface control box 232. One or more further alarms 60 may also be provided having one or more further alarm control boxes 332.
The surface control boxes 32, 132, 232 and 332 may be hardwired via cable 68 together and/or located within the same housing or provided by a single control box. Alternatively, these may be linked via wireless receivers 66.

[0140] A further optional modular element is the sonar trigger 70 which may be provided with its own surface control box (not shown) or connected via cable or otherwise to a designated master surface control box such as medium frequency alarm control box 32. Sonar trigger device 70 issues a sonar signal 72, and upon detecting objects such as objects 46A and 46B, determines the size, speed and direction of the object to assess if, according to various predetermined criteria, this can be attributed to a passing vessel or a passing seal or an approaching seal. Where an approaching seal 46A is detected, by sonar trigger device 70 a trigger signal is provided typically via a master control box such as medium frequency alarm control box 32.

[0141] In one aspect of the invention upon triggering of at least one trigger device 28 within the enclosure and/or or at least one trigger device such as sonar trigger device 70 outside the enclosure 10, one or more alarms may be triggered. In one aspect of the invention at least the electric net alarm device 40 is triggered and optionally also the medium frequency alarm 30 (preferably simultaneously or substantially simultaneously). Optionally a conditioning signal such as a pure single tone from the transducer of an acoustic alarm device may be provided preferably at the same time as the electric net alarm device, comprising an electrified net section, is activated.

[0142] To conserve power the electric net deterrent will preferably be provided in one or more electrified net sections that are powered one after the other. For example, section 140A may be powered initially and then after a period of time electrified net section 140B may be powered following re-moval of power from first electrified net section 140A. Alternatively, or in addition, within one or more or each electrified net section 140A, 140B, power may be provided to one or more conductors 62A to 62E, one after another, so say 62B following removal of power from 62A, 62C following removal of power from 62B and so on or power may be provided to alternate conductors. Thus 62A, 62C, 62E may be powered during a first period and, following removal of power from these conductors, conductors 62B and 62D
may be powered. Indeed, this rippling of power between conductors may occur during power provision to electrified net section 140A. During deliv-ery of power to electrified net section 140B, power may first be delivered to conductor 64A, then 64B, then 64C, then 64D or may be provided in groups such that a first group comprising e.g. a first pair of conductors 64A and 64C
are powered and then a second group comprising e.g. a second pair of conductors, 64B and 64D are powered. The nature of the power during any period of power delivery to any electric net section may be pulsed within any conductor or group of conductors as described elsewhere herein.

[0143] The lower the frequency the harder it is to generate sound at loud volume levels. To be effective, a low frequency acoustic alarm 50 needs to generate equivalent levels as a medium frequency acoustic alarm device 30. 190 dB may be required to deter at this lower frequency. The low frequency alarm device 50 typically requires a specifically designed hardware; in the form of a low frequency transducer 52' capable of transmit-ting frequencies in the lower register of 2-7kHz. This transducer is typically connected to additional surface control box 232 to supply appropriate power to the low frequency transducer, controlling the flow of electricity to power alarm device 50 and signals determining the output of the transducer 52'.
This tailor-made surface control box 232 may in turn be connected, either physically or wirelessly (using a radio transmitter), to a medium frequency or master surface control box 32. This connection will facilitate the low fre-quency transducer being triggered by the standard protocols in the medium frequency surface control box 32. The frequency generation (algorithm) may follow the same pattern as the medium frequency alarm device 30 (which may be a US3 available from Ace Aquatec Ltd), however the algorithms will be shifted down the frequency spectrum. In other words, instead of a lookup table of frequencies from 10-20kHz, a lookup table of frequencies of between 2-7kHz may be used. A randomisation algorithm may be used.

[0144] The electrified net sections may use conductors in the form of vertical strands of metal (e.g. stainless steel, copper or aluminium), or of other conductive material, woven into the net at around 100mm spacing. The spacing between conductors may be 50 to 1000mm, or 100 to 500mm, or 100 to 250mm. Preferably, a 2mm diameter wire conductor is used. Preferably, the conductors are made of 75% copper and 25% zinc alloy to reduce the ohmic losses. These may be individually connected to a microprocessor controlled distribution unit typically located within the electric net surface control box 132. The distribution unit may be configured to switch power (e.g. 24 to 48V, say around 36V DC source e.g. from 12V lead acid batteries or mains supply), to individual strands (e.g. conductors 140A to 140F and/or conductors 240A to 240H seen in Figure 9) in rapid succession ensuring that only a limited number of conductors are connected to the power source simultaneously, but that all conductors are connected to the source within a short time period. Optionally, within a net section only one pair of conduc-tors is powered at a given time, but all conductors are powered at least once during a period of power delivery ('T' - see Figures 12A to 12C) to that section. This scheme will provide distributed protection while minimizing the power requirement for powering the (now electrified) net 20.

[0145] The distribution unit in electric net surface control box 132 controls timing and polarity of electrical pulses fed into the various strand conductors (e.g. conductors 140A to 140F and/or conductors 240A to 240H
seen in Figure 9) woven in the netting. The polarity may be reversed sequen-tially therefore each conductor (not shown) may act alternately as cathode or anode, thereby minimizing the effects of hydrolysis and decay to the elec-trodes. While the current is flowing through a conductor, an electric field is created around it that should have a deterring effect on any marine mammal in contact or within a few inches of the strand. Any given conductor is expected to be powered using about 10 pulses per second with each pulse lasting for only a few milliseconds, preferably around one millisecond.
When this conductor is not powered, the neighbouring conductor will be powered, so the protecting electric field ripples rapidly around the protected area. For example, the power may be moved from one conductor to the next, sequentially or from one pair of conductors to the next pair of conduc-tors, sequentially. The conductor or pair of conductors may be neighbouring or there may be one or more further conductors in between (as explained in more detail in relation to Figures 11A to 11C). The control box will allow user controlled adjustment of the power settings, including pulse duration, pulse rate and power levels. Typically the device may be set to 100 hz, 200 microsecond pulses, and 36 volts delivered to conductors in sequence to a net section. For example, if 100 conductors are provided, within a period of power delivery of one second, ten pulses per second, each pulse of lms duration and, say, 30V height, may be delivered to each pair of conductors and then to the next pair of conductors (giving a root mean squared voltage of 3mV). Thus, each conductor receives 10 pulses of lms length during the period of power delivery of one second, each of the 100 conductors, or pair of conductors being powered out of sequence with the remaining conductors.

[0146] Optionally, a useful feature of this device is that it can be triggered by the designated master surface control box 32 through connecting the electric net surface control box 132 to designated master surface control box 32 , either with radio transmitter or through a wired connection. This allows the fish motion detector trigger device(s) 28, or a seal movement detector (sonar trigger device 70), to set off the electric net alarm device 40, thereby conserving power consumption on the electric net surface control box 132. Without this element the electric net 20 may be difficult to maintain because of high power consumption due to the salinity of the water.

[0147] The sonar trigger device 70 may be a simple transducer emitting a sound and receiving a reply to identify range (echo), speed (Doppler) and size (amplitude) of the object. In an example embodiment, a transducer emits sound at around 400kHz. It has a coverage of 120 degrees and can listen up to a range of around 50-100m. The Doppler shift allows the device to spot mammalian targets by recording echo (time), Doppler (speed) and amplitude (size).

[0148] The sonar trigger transducer (not shown) will typically be fitted underwater at a depth of around 1 to 5 m from the surface beside the fish farm cages. It will typically look out over 120 degrees, and sufficient quantities of transducers 52' may be required to provide full site coverage.
The sonar trigger device and integrated or separate transducer 52' is con-nected to a surface control box 232 supplying power and giving/receiving data from the transducer 52'. All data is recorded and a computer processor typically deciphers the data in the control box 232. The time it takes for an echo to be received allows the range of the object to be recorded. If the echo shortens indicating the object is closer than, for example, 50m then the control box 232 signals to the master surface control box 32 (either with radio telemetry or through a direct cable link). If the echo is of a larger amplitude than that emitted by, for example, a football sized object, the system may be instructed to signal a scram via one or both of the acoustic alarm devices 30, 50, presuming that such an object is likely to be a seal. If the object is of an amplitude larger than that produced by a seal-sized object then the system will typically be programmed to ignore this object, presuming it to be a boat hull etc. The Doppler device routinely ignores static data such as seabed and surface waves.

[0149] By pairing the device to the master surface control box 32, the sonar trigger device 70 can be configured to set off one or more of a standard acoustic scram on the submerged medium frequency alarm device, a sub-merged low frequency transducer (low frequency alarm device 50), the electric net alarm device 40, simultaneously, in some combination or in a successive sequence of some or all.

[0150] A multi-beam sonar device is another embodiment of a sonar trigger 70 which uses a standard multi-beam sonar, emitting sound which returns an echo. This echo is translated by a computer programme into a pictorial representation to a remotely or physically connected computing device e.g. a laptop. The software on the laptop generates a video represen-tation of what the device is seeing.

[0151] The software on the computing device then determines if the size, direction and proximity of the object is equivalent to the pre-programmed configuration for a "seal". It judges this on a sliding scale of likelihood, with, for example, red or 1 for non-seal, amber or 2 for a potential seal, and green or 3 for a definite seal identification. The comput-ing device can communicate with the master surface control box 32 via a radio transmitter or direct cable link, and can simply send a signal that can activate an acoustic scram from an acoustic alarm device, a low frequency variant, an electric net, or any combination of all.

[0152] The net 20 is converted into or formed as an electric net 20 by interweaving, for example, two sides of a 15x 15 meter square net with 2rnm metal (e.g. stainless steel, 75% copper/ 25% zinc alloy) vertical cords, spaced evenly every 100mm approximately. Each strand is tied off at the surface with appropriate connectors. Weaving can take place when existing nets are lifted for inspection (occurring once a month).

[0153] The electric net surface control box 132 incorporates an AC
mains cable for charging a series of 12 volt batteries. The box 132 may for example allow incorporation of four electric net systems in. Current can be directed to particular areas of the net at timed intervals. Each cluster of the net (electrified net section) will be activated for a brief period.

[0154] Stainless steel wire may be spaced every 100mm through the existing net and connected each approximate eight meter by three meter segment (electrified net section) to a separate power supply. Each power supply would be connected to a centralized top box (e.g. master surface control box 32) with the capacity to control frequency, pulse width and voltage. Pulses to an electrified net section may need to be relatively long (10 ms) to ensure lower voltages and spread out over the netting to reduce power consumption. Alternatively, a period of power delivery may be longer e.g. 1 to 5 or 6 seconds with pulses of e.g. 1 to 10 ms being delivered during the period of power delivery. 2min thick wire may be suitable as a compro-mise between requiring less voltage (1mm) and added strength (3mm) to prevent damage when a seal comes into contact with the netting.

[0155] By far the biggest challenge is the practical issues associated with creating electric fields in water. Water conductivity is very low in salt water environments so an impractical level of power would be required to electrify the whole net at any one time. The solution is to switch between various conductors. Switching effectively between the various conductors will introduce complexity which will need to be managed carefully so that enough deterring field is generated where it is needed. Factors (such as waveform, frequency and pulse width) may be adjusted to reduce any possible effect on fish health and appropriate deterrence of seals. Thus, one preferred solution is to pulse the electricity around (providing power to) segments (electrified net sections) of the net in quick succession. Alternatively or in addition, during a period of power delivery to any electrified net section, power may also be pulsed during that period of power delivery.

[0156] The master surface control box 32 or the electric net surface control box 132 is designed to allow precise settings, of parameters such as voltages, pulse durations and waveforms to precise areas of the net. The control box 32, 132 may allow AC mains connection and conversion to pulsed DC power to be supplied to an array of conductors (e.g. first and second conductors as described in relation to Figures 10A and 10E. An electric field probe may be used to test the voltage gradient of the fields generated by the equipment. Water conductivity measurements may be recorded and appropriate adjustment of the electrification parameters made.
Movement of fish away from the electric field may serve to push the fish away from the attacking seal.

[0157] Referring now to Figure 8, an alternative submerged fish enclo-sure 10 comprising a net 20 is shown. Net 20 has four generally triangu-lar-shaped sides 20A, 20B, 20C, 20D which meet centrally beneath a frame 22 to form an inverted apex thus providing an enclosed net 20 for holding fish therein. Four trigger devices 28 are suspended on a light line 26 from a horizontal rope 24 at a depth around half that of the net 20. Each of the generally triangular sides 20A, 20B, 20C, 20D of net 20 are provided with an array of conductors interwoven with the net to form electrified net sections 340A, 340B, 340C and 340D respectively.

[0158] Trigger devices 28 are three to five metres below the surface and are typically located below the feeding line. The electrified net sections may be electrified sequentially so, for example, upon triggering of a trigger device 28, a first electrified net section 340A may be powered. Following removal of power from electrified net section 340A, power is provided to electrified net section 340B optionally with a sequence of pulses during a period of power delivery or with a single pulse of power. Thus the power to electrified net section 340B may be delivered in a sequence of pulses. Where a se-quence of pulses is provided, this may be repeated in any period of power delivery to that net section. Following removal of power from electrified net section 340B power is delivered to electrified net section 340C again option-ally in a sequence of pulses or with a single pulse of power. Following removal of power from electrified net section 340C power is delivered to the fourth electrified net section 340D. This sequence of power delivery may be repeated such that following removal of power from electrified net section 340D, power is now delivered again to electrified net section 340A. The whole process repeats itself.

[0159] Control of the power to the electrified net section 340A, 340B, 340C, 340D is provided by an electric net surface control box 132 which typically has a control circuit optionally provided by a micro controller controlling the periods of power delivery to each of the electrified net sec-tions as well as the sequence of pulses within any period of power delivery (e.g. a single pulse, period of continuous power delivery or a sequence of pulses). As will be apparent to someone skilled in the art, from the informa-tion disclosed herein, the delivery of power to one electrified net section need not be to a neighbouring electrified net section but rather to an opposing electrified net section, e.g. following removal of power from electrified net section 340A, power may be delivered to electrified net section 340C, power may then be delivered to electrified net section 340B and subsequently, following removal of power from that electrified net section, to electrified net section 340D opposite to it. Alternatively, power may be delivered to groups of net sections, e.g. power may be delivered to electrified net section 340A
and 340C forming a first group and, following removal of power from electrified net section 340A, 340C, power may be delivered to electrified net sections 340B and 340D. In this way, power ripples about the net typically, without the need to power the entire net at once. Nevertheless, in one optional embodiment of one aspect of the invention it is envisaged that the entire net may be electrified (forming a single electrified net section) option-ally being powered following activation of a trigger device. In a further aspect of the invention in which it is desired to be more power efficient, power is provided to at least two or more electrified net sections optionally sequentially.

[0160] By removal of power from an electrified net section (or conduc-tor or pair of conductors or group of conductors), it is meant that sufficient power has been removed from that section (or conductor or pair of conduc-tors or group of conductors) to enable the power supply to supply another electrified net section (or conductor or pair of conductors or group of conduc-tors) without undue burden. This will depend upon the size of the net section, the number of net sections, the conductivity of the water, the thick-ness of the conductors within each electrified net section, the strength of the power source and other factors as would be understood by someone skilled in the art. Typically, power is completely removed from one electrified net section before delivery of power to a further electrified net section. A short time delay may be provided of a few tens or hundreds of micro seconds, or even a few seconds. It may be preferable, however, to provide power to a further electrified net section within a fraction of a second of removal of power from a preceding electrified net section or before power is completely removed. The period of power delivery to any particular electrified net section may be a fraction of second, e.g. 0.25s, 0.5s, 0.75s but is more preferably 1 to 20s, more preferably 1 to 5s.

[0161] Thus, in this preferred embodiment of one aspect of the inven-tion, power 'ripples' around the net from one electrified net section to another at a sufficient speed so that to an approaching predator it appears in effect that the entire net is electrified. Nevertheless, by passing the power between electrified net sections rather than to the whole net at one time, the power burden on the power supply is considerably reduced. Indeed, as an alternative or in addition, within an electrified net section, power may be "rippled" around from one conductor or pair of conductors or group of conductors to the next to reduce the power burden.

[0162] Referring now to Figure 9, an alternative embodiment of one aspect of the invention is shown in which a net 20 is provided with an array of single conductors, a first series of generally horizontal single conductors 140A to 140F and a second series of generally vertical conductors 240A to 240H. Horizontal conductors 140A to 140F are spaced vertically about the periphery of net 20. Conductors 240A to 240H are spaced horizontally about the periphery of net 20. Either one or both series of conductors 140A to 140F and/or 240A to 240H may be provided. Whilst the number of conduc-tors required is not fixed, it is preferred that the entire net 20 is provided with conductors. Various examples of the spacing of the conductors is described elsewhere herein.

[0163] Each conductor 140A to 140F and 240A to 240H provides in essence a linear conductor about which an electric field is formed when a current is passed through the conductor (e.g. from a power source located within an electric net surface control box 132). In accordance with one embodiment of one aspect of the invention power, may be provided to conductor 140A and then, following removal of power from that conductor, to conductor 140B and then, following removal of power from conductor 140B, to conductor 140C and so on. Alternatively, power may be provided to groups of conductors such as 140A, 140C and 140E (e.g. substantially simultaneously or in sequence) and then, following removal of power from that first group of conductors, power may be provided to conductors 140B, 140D and 140F (e.g. substantially simultaneously or in sequence forming a second group of conductors. Thus, an electrified net section is provided in the region surrounding a powered conductor.

[0164] Similarly power may be provided to generally vertical conduc-tors 240A to 240H in sequence from 240A to 240B to 240C and so on, or may be provided to groups of conductors, e.g. to a first group comprising 240A, 240D and 240G and then to a second group comprising 240B, 240E
and 240H and then to a third group comprising 240C, 240F and 240A and so on.

[0165] In one example embodiment, an electrified net section is pro-vided about each conductor when a current is passed through that conductor generating an electric field in the vicinity of the conductor in the region of that portion of the net adjacent the conductor. Some of the possible alterna-tive preferred embodiments are described in relation to Figures 10A to 10E.

[0166] The current may be passed from one conductor to another, or from one group of conductors to another, on the order of a fraction of or a few micro seconds, a few tens of micro seconds or a few hundreds of micro seconds or several hundreds of microseconds. Preferably power will be passed from one conductor to another, so that within a predetermined period of time, say 1 to 20s or more preferably 1 to 10 s or 1 to 5s each conductor within a group or within an electrified net section or within the electric net is powered at least once. Thus to an approaching predator power appears to be present quasi continuously.

[0167] Figures 10A to 10E show example arrangements of switching arrangements and power supplies for a series of first conductors interwoven in a net to form an electric net having an electrified net section and a second conductor (typically external to the net) between which an electric field can be formed. Optionally voltages of up to e.g.48V, typically up to 36V, may be used in each pulse of power, the voltage being applied between a first conductor and a second conductor, optionally the second conductor being located external to the electrified net section.

[0168] In Figures 10A to 10E, four first conductors 440 are provided woven into a region of net (not shown) to form an electrified net section. A
second conductor 442, typically located external to the net in a region close to the electrified net section, provides a conductor of opposing polarity (to first conductors 440 - here 440A to 440D) so that when power is applied to one or more first conductors 440, an electric field may be formed there between. A
power supply 448 delivers power to conductors 440A to 440D via control switches 444, and in this example embodiment, via an H-bridge 446. Control switches 444 are controlled by a control means (not shown) typically pro-vided by a microprocessor and programmable by a user. Power may be delivered to first one conductor 440A, then upon removal from 440A, to 440B and so on, the power delivery being controlled by control switches 444 (here AC solid state relays). H-bridge 446 can be used to alternate the polarity of the voltage applied to first conductors 440A to 440B, optionally upon each pulse of power to the first conductors and/or from one period of power delivery to the next (e.g. where a period of power delivery comprises a sequence pulses). Second conductor 442 may be a zinc electrode.

[0169] Figure 10B is similar to Figure 10A, but control switches 445 (here two per conductor) are here provided by DC solid state relays and the H-bridge has been replaced with four DC solid state relays 442.

[0170] In Figure 10C, +/-10 power from power supply 448 is provided and control switches are DC SSR solid state relays. In Figure 10D, one H-bridge 446A to 446D is shown per conductor 440A to 440D respectively.
In Figure 10E, an AC supply and transformer 450 is used along with AC
solid state relays (or thermistors) 447 to deliver power to first conductors in accordance with the invention.

[0171] Referring now to Figures 11A to 11C, a low impedance power supply (not shown) of around 10 kW may be used to power conductors in the sea water to deter seals from contacting the netting. This power may be distributed around the enclosure as a ring main 544 and tapped off at intervals by local switching boxes 542 located on the periphery of the pen. Each switching box 542 will be connected to around 20 conductors, optionally arranged in pairs. 100 to 200 conductors may be used, optionally arranged in pairs. The number of conductors used in one enclosure or in one net section may be, for example, 5 to 200 pairs, 10 to 100 pairs, 20 to 100 pairs, 20 to 50 pairs, 20, 50 or 100 pairs. These conductors are typically flexible, partially sheathed electrode cables and these will be spaced woven into the mesh of the netting at intervals of somewhere between 50 to 1000mm, or preferably 100 to 500mm or more preferably 100 to 250 mm. These may be powered in sequential pairs with preferably only a single pair of electrodes powered at any one time. The power may be delivered in pulses. The pulses may alternate in polarity to minimise erosion and hydrolysis. The pulses may be milliseconds long, have a peak voltage around 30V and be applied at a frequency of around 10 Hz. For example to achieve a root mean square voltage of 3mV in 100 pairs of electrodes, 10 electrical pulses per second may be applied with each pulse lasting lms and having a voltage of 30V.
Areas of the sea pen will be powered for a period of about one second and then the power will be transferred to other areas for up to 5 seconds. By distributing the power in this way, the 10 kW power source is expected to be sufficient to protect the sides and bottom of a 90m diameter enclosure.

[0172] Communication, timing and electrode pair selection will be a determined by a central microprocessor based controller (e.g master surface control box 32 or electric net control box 132, see Figure7). The control signals may be transmitted over a pair of dedicated wires, however, commu-nication over the power cables may be possible. Low voltage drop MOSFETs developed for the automotive industry may be used for current switching.

[0173] The impedance between the conductors has been modelled to including the ohmic losses in the conductive material. This shows that, for example, using 2mm diameter electrodes of a 75% copper, 25% zinc alloy will result in only 12% voltage drop over the 4m length of the conductor, whereas the same size conductor made of stainless steel would result in a higher (e.g. 68%) drop in voltage.

[0174] Controlling corrosion particularly at electrical junctions will be important to ensuring this system has useful working life. Precautions will include careful selection of materials, the use of galvanic protection and rigorous exclusion of water from mixed metal junctions.

[0175] Referring now to Figures 11A to 11C in detail, a ring main 544 may be provided about the periphery of an enclosure. Within one enclosure section of the enclosure, several vertical conductors 540A to 540F (here six are shown) are powered by the ring main 544 from which power is tapped by local switching boxes 542. In Figure 11A, the conductors are arranged in

[0176] An alternative arrangement of pairs is shown in Figure 11B.
Here each conductor forms part of two neighbouring but not overlapping

[0177] An alternative arrangement of pairs is shown in Figure 11C.
Here each conductor forms part of two neighbouring and overlapping pairs of conductors. The pairs may be powered sequentially, for example pair 1, then pair 2, then pair 3, then pair 4, then pair 5 and so on. Here, an active electrified area bounded by a powered pair of conductors (e.g. pair 1) overlaps with the next active electrified area bounded by the next pair of conductors (e.g. pair 2) powered in the sequence.

[0178] In Figure 12A a period of power deliver T to a series of pairs of conductors (pair 1 to pair 5) comprises single pulses 546 of equal height and length forming a sequence of pulses 600 delivered access pairs 1 to 5. A
single pulse is delivered to pair 1 and then when this is removed, an identical pulse is delivered to a pair 2 and so on. The sequence is repeated (optionally with a small pause in between) in a second sequence 602. It will be appreci-ated by those skilled in the art that the number and/or height and/or length and/or shape of pulses within a sequence 600, 602 may be varied to improve the effectiveness as a deterrent and/or to reduce the power consumption and/or for other technical reasons. Indeed, a series of pulses 604 identical to the first but of opposite polarity may be provided across the pairs of conduc-tors instead of a identical second sequence 602 to assist with reducing corro-sion effects.
[01791 Figure 12B shows three spaced identical pulses 548 forming a sequence of pulses 606A delivered to pair 1 initially. Following removal of power from pair 1, a further identical sequence 606B of pulses 548 is deliv-ered to pair 2. Following removal of power from pair 2, a further identical sequence 606C of pulses 548 is delivered to pair 3, and so on. Thus, in Figure 12B, sequences 606A to 606E are delivered during a period of power delivery T to the net section comprising pairs 1 to 5.
[0180] In Figure 12C, a first sequence 600 of, here identical, pulses 550A, 550B is delivered to pairs 1 to 5 sequentially one after the other.
Then, a second sequence 602 of, here identical, pulses 550A, 550B is delivered to pairs 1 to 5 sequentially one after the other. The pulses 550A, 550B are of opposite polarity to assist with reducing corrosion effects.
[0181] Referring now to Figures 13A to 13C, alternative arrangements of conductors are shown. Typically, as in Figure 13A, a pair of conductors 640A, 640B are powered from a voltage source, for example, of 30 volts.
As an alternative in Figure 13B, the supply voltage is doubled and applied across two conductor pairs 740A, 740B and 740B, 740C. Thus, +30 volts is applied to conductor 740A, and -30 volts is applied on conductor 740B with intermediate conductor 740B either left floating, connected to other interme-diate electrodes e.g. as a local earth, or just left electrically isolated. In this latter case the potential of the intermediate electrode 740B will be fixed by the aqueous impedance of its whole length to the powered electrodes 740A, 740C, and any predator coming into contact with it can only make a local disturbance to the field, just as it would if the conductor were powered.
[0182] A further alternative is shown in Figure 13C in which further "floating" intermediate conductors could be used with a proportionate increase in electrical supply voltage and so increase the scanning speed at the same current. For example, +/- 60 volts could be provided across a group including three floating intermediate conductors 840B between powered electrodes 840A and 840C. This "floating" conductor arrangement offers a substantial simplification of the net manufacture and installation.
[0183] In terms of pulse length it may be appropriate to operate with pulse length of between 10 and 500 microseconds, the energy delivered in joules per pulse (which is proportional to voltage, V' x pulse length, T) being thought to be the deterrent factor. To provide, for example, 70 microseconds pulses, and to provide an equivalent amount of energy as a one millisecond pulse at 30 volts, which is thought to provide a suitable deterrent, then, (1000/70)1/2 is needed, equal to 114 volts. The required pulse current goes up from 100 amps to 380 amps but this could be supplied for the required 70 microseconds by a local capacitor, or other energy storage devices. For example, with a voltage drop of 10%, a capacitor of 2200 microfarads could be used to supply this current. Thus, a local capacitor could be provided to reduce the requirement for a thicker supply cable, further reducing the power burden required of the power supply.
[0184] Power and/or switch control systems may be located centrally or may be located in a distributed arrangement around the enclosure and alterna-tively, or in addition, may be provided sub-surface. A de-centralised power supply would be able to distribute power at a higher voltage to reduce losses.

As an example, 440 volt three phase, 3 wire power distribution with local switched mode power supplies in submerged stainless steel enclosures may be used.
[0185] Turning now to Figure 14, a top level schematic view of an enclosure 10 and an electric net control system 132' is shown. Part of the electronics of control system 132' is provided in a surface control module 132A linked to a computer for controlling power delivery to a corresponding outstation 132B located on enclosure 10 (typically one of several outstations distributed around enclosure 10). Outstations 132B, where provided, may provide switching capability and/or operate as local power supplies to one or more electrified enclosure sections. Outstation 132B powers in this, example embodiment, twenty-eight conductors (also known as electrodes) 40A within an electrified enclosure section. As an example, fifteen outstations 132B
each powering, and controlling delivery of power to, twenty-eight conductors may be provided.
[0186] Figure 15B shows examples of the types of logic that may be used to control outstation 132B, the control signals coming from surface control module 132A. Data 400 is passed to de-coders 402A powering 'odd' electrodes, numbered 1 to 27 (of which there are 16) and to de-coder 402B
controlling 'even' electrodes numbered 2 to 28 (of which there are 16). The polarity of the conductors within one outstation may be in sync with the polarity of the conductors in an adjacent outstation to allow hand over from one electrified enclosure section to the next, in a preferred embodiment.
Control data 404 may be used to inverse the polarity or clear local faults.
Starting with labelled polarity, successive bytes from the master control increment the 'odd' and 'even' de-coders. Once the sequence has passed through this outstation, a byte, for example, "11110000" is sent to invert the `odd/even' polarity ready for the next time this outstation is activated.
[0187] Figure 16 shows details of the energising of ten conductors in an outstation and use of conductive communication to indicate when an outsta-tion is to energise its conductors by sensing voltage leakage from a previous (typically a neighbouring outstation). In step 498 the last conductor (prefera-bly a conductor and/or pair of conductors of a previous outstation) is energised. Here, the last electrode of the previous outstation is 940A and the first conductor of this outstation is 940B form a pair. Communication is facilitated between adjacent outstations by sensing the voltage leakage from the previous outstation. It may be appropriate to provide a "start" mecha-nism even after a random period of (long) inactivity or by a "master" outsta-tion following power up or, indeed, following a trigger signal as described elsewhere herein. Fault detection may be carried out via power over current and/or under current trip, with fault location being carried out by current pulse counting. In step 500, this outstation commences energising of its electrodes. In step 502, a wait of T/2 seconds is optionally allowed. In step 504, a first conductor/conductor pair is energised. In step 506, the next conductor/conductor pair is energised, (e.g. comprising one conductor of a preceding pair). In step 508, the third conductor/conductor pair is energised (e.g. comprising one conductor of a preceding pair), and so on in steps 510, 512, 514 until the tenth conductor/conductor pair is energised in step 516. It may be that power is completely removed from a preceding conduc-tor/conductor pair before a later conductor/conductor pair is energised.
However, it is sufficient that power is not supplied to all the conductors at one time and typically, at least one conductor/conductor pair will have had power removed from it before power is supplied to a later conduc-tor/conductor pair. This may be the case even though other intermediate conductors/conductor pairs may have been energised in the meantime.
[0188] A useful kind of composite cable, with a mixture of thin and thick conductors, may be used with, for example, 3 x 6 mm2 cores and a single 0.5 mm2 core. Thus, a single composite cable may be used to provide both power and communication when woven into the net.
[0189] Thus, in one or more embodiments of the invention, to an approaching predator, preferably most or all of the net 20 will appear electri-tied to an approaching predator whilst reducing the burden on a power supply providing power to the conductors. In particular, by providing a triggered electric enclosure alarm device and/or separate conductors or groups (e.g.
pairs) of conductors, powered at different times and/or separate electrified enclosure sections powered at different times, the power burden on a power supply can be reduced, facilitating use of an electric net in salt water.
Furthermore, providing an electric net enclosure alarm device and a condi-tioning signal optionally triggered at or around the same as an alarm device, preferably the electric net alarm device, reduces the likelihood of habituation.
[0190] Various alternative embodiments to the invention will be appar-ent to those skilled in the art from the information disclosed herein; all such alternative embodiments are intended to be covered by the appended claims.
For example, the submerged portions of an enclosure may all be electrified forming an integral electrified enclosure section. This does not mean that each strand of the net has a conductor woven therein but rather that sufficient conductors are woven into the net throughout the electrified enclosure section to form an effective deterrent. This may depend on the nature of the conduc-tors, separation of the conductors, thickness, applied field strength, pulse parameters, water conductivity etc. The roof of the enclosure may be electrified.

Claims (63)

WHAT IS CLAIMED IS:

1. A predator deterrent system for a submerged fish enclosure compris-ing:
at least one trigger device configured to detect a predator in the vicinity of a fish enclosure; and configured to generate an alarm signal responsive to the detection of the predator; and at least one alarm device responsive to the alarm signal generated by the trigger device, the alarm device comprising at least one electrified enclosure section wherein upon receipt of an alarm signal generated by the trigger device at least one electrified enclosure section is powered.

2. A system according to claim 1 comprising a control means for control-ling delivery of power to the at least one electrified enclosure section.

3. A system according to claim 2 in which at least one electrified enclo-sure section comprises two or more conductors;
and in which the control means is configured to supply power to one or more predetermined conductor(s) in the electrified enclosure section following removal of power from one or more preceding predetermined conductor(s) in the same electrified enclosure section.

4. A system according to claim 3 in which the conductors are grouped in at least two groups, each group comprising one or two or more con-ductor(s) and in which the control means is configured to supply power to the conductor(s) in one group following removal of power from the conductor(s) in another group.

5. A system according to claim 4 in which the groups comprise 2 or 3 or 4 or 5 or 6 conductors.

6. A system according to claim 3 or 4 in which at least one electrified enclosure section comprises two or more groups of conductors, each group consisting of a pair of conductors and when power is supplied to a group, a potential is applied between the pair of conductors in that group.

7. A system according to any one of claims 2 to 6 comprising:
two or more electrified enclosure sections; and in which the control means is configured to supply power to one or more predetermined electrified enclosure section(s) following removal of power from one or more predetermined preceding electrified enclosure section(s).

8. A system according to claim 7 in which the electrified enclosure sections are grouped in at least two groups, each group comprising one or two or more electrified enclosure section(s) and in which the control means is configured to supply power to the electrified enclosure sec-tion(s) in one group following removal of power from the electrified enclosure section(s) in another group.

9. A system according to claim 8 in which a group comprises 2 or 3 or 4 or 5 or 6 electrified enclosure sections.

10. A system according to any one of claims 6 to 8 in which the electrified enclosure sections are grouped in at least two groups and in which the control means is configured to supply power to one electrified enclo-sure section within a group following removal of power from another electrified enclosure section within the same or a different group.

11. A system according to any preceding claim in which at least one electrified enclosure section comprises one or more conductors, which conductors are first conductors having a first polarity, and the system further comprises at least one second conductor separate from the electrified enclosure section, optionally externally located to the enclo-sure, at least one second conductor having a second polarity opposite to the first.

12. A system according to any one of claims 1 to 10 in which within an electrified enclosure section at least two or more conductors are pro-vided and the conductors are arranged in pairs, each conductor in a pair having a different polarity.

13. A system according to claim 11 or 12 in which the polarity of the first and second conductors are reversed periodically.

14. A system according to any preceding claim in which power is provided to an electrified enclosure section following triggering.

15. A system according to any preceding claim in which power is provided to an electrified enclosure section for a predetermined period of time.

16. A system according to any preceding claim in which power is supplied intermittently to one or more electrified enclosure sections.

17. A system according to any preceding claim in which, within a period of power delivery, power is supplied in pulses.

18. A system according to claim 16 in which power is supplied in pulses and the pulse lengths are 10µs to 1500µs or 200µs to 1000µs or 1000µs and/or the pulse voltage is 6 to 42V or 24 to 36V or 30V and/or the root mean square voltage is between 2mV to 8mV or between 3mV to 6mV or is 3mV.

19. A system according to claim 17 or 18 in which the frequency of the pulses is 5 to 500Hz or 50 to 100Hz or 10Hz.

20. A system according to claim any one of claims 17 to 19 in which power is provided in a predetermined sequence of one or more pulses during a period of power delivery to an electrified enclosure section.

21. A system according to claim 20 in which the predetermined sequence of one or more pulses is applied to a first pair of conductors in an electrified enclosure section then to a further pair of conductors in the same electrified enclosure section.

22. A system according to any preceding claim, in which there are two or more pairs of conductors and power is supplied to two or more or each pair sequentially within the electrified enclosure section.

23. A system according to claim 21 or 22 in which one or more or each pair of conductors comprises a conductor that also forms part of another pair of conductors.

24. A system according to claim 21 or 22 in which the conductors of one or more or each pair of conductors do not form part of another pair of conductors.

25. A system according to any one of claims 21 to 24, in which the area lying bounded by one or more or each pair of conductors overlaps with the area bounded by one or more pairs of other conductors.

26. A system according to any preceding claim in which one or more electrified enclosure sections are two or three dimensional.

27. A system according to any preceding claim in which at least one trigger device is configured to detect motion of fish to generate an alarm signal and/or in which at least one trigger device is configured to detect a predator to generate an alarm signal.

28. A system according to claim 27 in which at least one trigger device comprises a sonar trigger device having at least a sonar receiver for receiving sonar signals indicative of the presence and/or motion of a predator.

29. A system according to claim 28 in which the sonar trigger device comprises an integrated sonar emitter.

30. A system according to claim 29 in which at least one sonar emitter, separate from the sonar trigger device, is provided, the sonar trigger device comprising a sonar receiver.

31. A system according to any preceding claim in which at least one trigger device is configured to generate an alarm signal upon at least one predetermined condition state being activated.

32. A system according to claim 31 in which at least one predetermined condition state comprises one or more of:

level of fish motion detected;
size of a passing object;
direction of movement of a passing object;
speed of movement of a passing object.

33. A system according to any preceding claim in which a single electri-fied enclosure section forms substantially all the sides, or substantially all the sides and base, of an enclosure.

34. A predator deterrent system for a submerged fish enclosure compris-ing:
at least one electrified enclosure section;
a control means for controlling delivery of power to the at least one electrified enclosure section.

35. A system according to claim 34 in which at least one electrified enclosure section comprises:
two or more conductors; and in which the control means is configured to supply power to one or more predetermined conductor(s), in the electrified enclosure section following removal of power from one or more preceding predetermined conductor(s) in the same electrified enclosure section.

36. A system according to claim 35 in which the conductors are grouped in at least two groups, each group comprising one or two or more con-ductor(s) and in which the control means is configured to supply power to the conductor(s) in one group following removal of power from the conductor(s) in another group.

37. A system according to claim 35 in which the groups comprise 2 or 3 or 4 or 5 or 6 conductors.

38. A system according to claim 36 or 37 in which at least one electrified enclosure section comprises two or more groups of conductors, each group consisting of a pair of conductors, and when power is supplied to a group, a potential is applied between the pair of conductors in that group.

39. A system according to any one of claims 34 to 38 comprising:
two or more electrified enclosure sections; and in which the control means is configured to supply power to one or more predetermined electrified enclosure section(s) following removal of power from one or more predetermined preceding electrified enclosure section(s).

40. A system according to claim 39 in which the electrified enclosure sections are grouped in at least two groups, each group comprising one or two or more electrified enclosure section(s) and in which the control means is configured to supply power to the electrified enclosure sec-tion(s) in one group following removal of power from the electrified enclosure section(s) in another group.

41. A system according to claim 40 in which a group comprises 2 or 3 or 4 or 5 or 6 electrified enclosure sections.

42. A system according to any one of claims 40 to 41 in which the electri-fied enclosure sections are grouped in at least two groups and in which the control means is configured to supply power to one electrified enclosure section within a group following removal of power from another electrified enclosure section within the same or a different group.

43. A system according to any one of claims 34 to 42 in which at least one electrified enclosure section comprises one or more conductors, which conductors are first conductors having a first polarity, and the system further comprises at least one second conductor separate from the electrified enclosure section, optionally externally located to the enclo-sure, at least one second conductor having a second polarity opposite to the first.

44. A system according to any one of claims 34 to 43 in which within an electrified enclosure section at least two or more conductors are pro-vided and the conductors are arranged in pairs, each conductor in a pair having a different polarity.

45. A system according to claim 43 or 44 in which the polarity of the first and second conductors are reversed periodically.

46. A system according to any one of claims 34 to 45 in which power is supplied intermittently to one or more electrified enclosure sections.

47. A system according to any one of claims 34 to 46 in which power is provided for a predetermined period of time to an electrified enclosure section.

48. A system according to any one of claims 34 to 47 in which, within a period of power delivery, power is supplied in pulses.

49. A system according to any one of claims 48 in which the pulse lengths are 10µs to 1500µs or 200µs to 1000µs or 1000µs and/or the pulse voltage is 6 to 42V or 24 to 36V, or 30V and/or the root mean square voltage is between 2mV to 8mV or between 3mV to 6mV or is 3mV.

50. A system according to claim 48 or 49 in which the frequency of the pulses is 5 to 500Hz or 50 to 100Hz or 10Hz.

51. A system according to any one of claims 34 to 50 in which power is provided in a predetermined sequence of one or more pulses during a period of power delivery to an electrified enclosure section.

52. A system according to claim 51 in which the predetermined sequence of one or more pulses is applied to a first pair of conductors in an electrified enclosure section then to a further pair of conductors in the same electrified enclosure section.

53. A system according to any one of claims 34 to 52, in which there are two or more pairs of conductors and power is supplied to two or more or each pair sequentially within the electrified enclosure section.

54. A system according to claim 52 or 53 in which one or more or each pair of conductors comprises a conductor that also forms part of another pair of conductors.

55. A system according to claim 52 or 53 in which the conductors of one or more or each pair of conductors do not form part of another pair of conductors.

56. A system according to any one of claims 52 to 55, in which the area lying bounded by one or more or each pair of conductors overlaps with the area bounded by one or more pairs of other conductors.

57. A system according to any one of claims 34 to 56 in which one or more electrified enclosure sections are two or three dimensional.

58. A method of deterring predators for a submerged fish enclosure having a predator deterrent system comprising at least one electrified enclosure section, the method comprising: activating the at least one electrified enclosure section to deter predators.

59. A method according to claim 58 comprising:
controlling delivery of power to the at least one electrified enclosure section and supplying power to one or more pre-selected conduc-tor(s) in the electrified enclosure section following removal of power from one or more preceding pre-selected conductor(s) in the electrified enclosure section.

60. A method according to claim 58 or 59 comprising:
controlling delivery of power to two or more electrified enclosure sections; and supplying power to one or more pre-selected electrified enclosure section(s) following removal of power from one or more pre-selected preceding electrified enclosure section(s).

61. A method according to any one of claims 58 to 60 comprising using any of the features of claims 1 to 57.

62. A method of manufacturing a predator deterrent system for a sub-merged fish enclosure comprising providing a predator deterrent system having any of the features of claims 1 to 57.

63. A modular kit for a predator deterrent system according to any of claims 1 to 57 comprising at least one alarm device as described herein; at least one trigger device as described herein; wherein at least one alarm device comprises an electric enclosure alarm device having at least one electrified enclosure section.