AU746532B2 - A trawl net and method - Google Patents

Description

V

a 0

AUSTRUALIA

Patents Act 1990 STANDARD PATENT SPECIFICATION Invention Title: A TRAWLING NET AND METHOD This invention is described in the following statement: 4 2 THIS INVENTION relates to a bycatch reduction device (BRD) for use in a trawl net, a trawl net to which the BRD has been fitted and a method of retrieving a trawl net by a fishing vessel.

The present invention will be described with particular reference to a BRD, trawl net and method for trawling prawns. However, it will be appreciated that the invention may also be suitable for use when trawling for other marine animals and no limitation is intended thereby.

Trawl nets which are currently in use typically have a forward section with an open leading end. The forward section tapers from the io opening towards a narrow section. From the narrow section, the net then expands again in diameter to an enlarged rear end. This enlarged end is commonly known as the cod end. In use, prawns which enter the open end are funneled through the narrow section and into the cod end where they are contained until the net is retrieved by the fishing vessel. The prawns are then S• 15 released from the cod end.

It is also known to provide by catch reduction or exclusion devices which reduce bycatch and exclude large animals, such as turtles and fish from entering the cod end. Such devices typically have a grid located in o the narrow section of the net. The grid has a series of parallel bars. The spacing between the bars is selected such that prawns can pass between the bars but larger animals or fish are excluded. An escape opening or slit is o:"i provided in the trawl net and is located adjacent and forward of the grid. The location of the escape opening and the inclination of the grid are each arranged such that turtles or the like are directed by the inclination of the grid towards the escape opening.

The forward section of the net typically includes a funnel which directs captured animals towards a section of the grid. These funnels are designed to direct the prawns through the grid and away from the escape opening. In order for large animals such as turtles to reach the escape opening, the funnel must terminate some distance before the grid to allow a turtle to pass between the funnel and the grid towards the escape opening.

However, in use, a percentage of the prawns does not pass through the grid 3 but instead, escapes through the escape opening with the turtles. This results in a decrease in the total prawn catch, which is undesirable.

It is therefore an object of the present invention to provide a bycatch reduction or exclusion device and a trawl net fitted with such a device which may at least partially overcome the above disadvantages or provide the public with a useful choice.

According to a first broad form of the invention, there is provided a section of a trawl net for prawns or other animals, the section having a leading end and a trailing grid, the grid having a plurality of bars spaced to allow prawns or other desired animals to pass therethrough, but can exclude larger animals from such passage, the section including an escape means located adjacent the grid and a guide, the guide having a forward end attached to the leading end and which can extend through the section towards S* the grid such that a channel is defined between the guide and an outer wall of the section and when in use, animals entering the leading end are directed through the channel towards the grid; whereby the guide has a free end which is movable between a closed position in which the free end abuts the grid and an open position, and the free end is normally maintained in the closed V position by water pressure when the device is in use, but can be urged to the 0 00o 20 open position by animals or objects which enter the channel but are excluded from passing through the grid to allow the excluded animals or objects to pass between the free end of the guide and the grid towards the escape means.

The grid is typically inclined to direct larger animals towards either the top or the bottom of the net towards an escape means provided in the top or the bottom of the net respectively. Preferably, the escape means is located at the bottom of the net. A bottom exit allows debris to be released through the escape means. Typically, the grid is inclined towards the escape means. Typical inclination angels are between about 30o to about 600, preferably about The escape means may be an opening of a suitable size and configuration to allow larger animals such as turtles and larger fish to escape.

The escape opening may be a simple opening, slit, funnel or may have an enclosure which can be easily displaced by a moving animal.

The guide may be of any suitable design, providing it has a free end which can be held against the grid by water pressure as the net is being pulled through the water. Typically, the guide is a length of netting or a flexible plastics material attached in part to opposed side walls of the leading end. The guide may be pushed away from the grid to allow animals which are excluded from passing through the grid to pass along the front face of the grid towards the escape opening.

The section of the invention may be manufactured as a discrete section in which case a closed (or cod) end may be attached at a later stage.

A forward end of a net may also be attached, but this may not be necessary if the leading end of the section is of an appropriate size. Alternatively, a trawl net can be manufactured with the section in situ.

According to a further broad form of the invention, there is provided a trawl net which includes the section of the first broad form and a **•trailing closed end such that prawns or animals which pass through the grid S.are collected in the closed end.

The leading and closed ends of this trawl net may be of conventional net design. Typically, the net has a wide opening at the leading end which decreases in diameter towards the grid.

Loss of prawns from conventional nets can also occur during retrieval of the net by the fishing vessel. As the net is retrieved by the vessel, some prawns may escape through the net opening which remains open. This can be a significant problem in rough conditions. The conventional method of retrieving a trawl net is by the use of lines attached about the opening.

However, the present inventor has observed that loss of prawns through the opening may at least partially be alleviated by retrieving the net by means of a line attached to the grid. Retrieval in this manner essentially allows the net opening to close and reduce or avoid the loss of prawns therethrough. Thus, a preferred net of the present invention includes a retrieval line attached to the grid. Typically, the grid is provided with attachment means for attaching a retrieval line.

According to a further broad form of the invention, there is provided a method of retrieving a trawl net which has a leading open end, a trailing closed end and a grid intermediate the leading and trailing ends, the method including attaching a retrieval line to the grid and retrieving the net by said line.

It will be appreciated that such a method of retrieval may also be applied to conventional trawl nets. This method of retrieval allows the net to be lifted aboard the fishing vessel by the line attached to the grid. This minimizes uncontrolled movement of the grid on the deck. Uncontrollable movement of grids during conventional retrieval methods can impose a significant safety risk for deck hands.

By way of example only, the present invention will be described with reference to the figure which is a schematic drawing of a trawl net having S• a preferred section of the present invention fitted thereto.

15 The figure is a schematic illustration of a trawl net 11. For ease of illustration, the net has been illustrated as a cylinder of constant cross section, however, it will be appreciated that the net may also be narrowed towards the center portion.

S•The net has an open end 12 through which prawns and other animals may pass. The open end may have a metal chain attached to its lower edge (not illustrated) which is commonly known as a "tickler". The tickler is dragged along and generally sinks a couple of inches into the sea bed, thereby releasing prawns from their holes. At the opposite end of the net is a closed trailing end or cod end 13 in which the prawns are eventually contained. The net has a grid 14 which separates the net into a forward end and a cod end 13. The grid 14 is inclined at an angle of about 450. The grid has a series of equally spaced parallel bars. The bars are spaced to allow prawns to pass therethrough, but will exclude the passage of larger animals such as turtles and larger fish.

The net includes a guide means 16 which is in the form of a separate piece of netting which is attached at one end near the bottom edge of the open end 12 of the net 11. The guide 16 is gradually angled upwards 6 towards the upper wall 17 of the net. This guide means directs prawns and other animals which enter the open end 12 in the direction of arrow A. The guide 16 is attached to opposing sides of the net until about 1/3 of the way down the horizontal profile, at about the position marked by B. The remaining portion 18 of the guide is not fixed and is free to move towards and away from the grid 14. Under normal operating conditions, as the net is trawled in the forward direction, the free end 18 of the guide 16 is pushed against the surface of the grid by the water pressure. This means that the prawns entering the forward section of the net are guided by the guide through the grid 14 and into the cod end as indicated by the arrows marked C. It can be seen that in this case, it is not possible for prawns to escape between the abutting surface of the guide and the grid.

*In the event that a turtle or large fish enters the net, the turtle is also directed towards the grid by the guide. However, the turtle or other large animal is unable to pass through the grid and is forced downwards. As the end of the guide is free, the turtle is able to force its way between the free end of the guide and the grid. The dotted lines F illustrate the free end 18 in two different open positions. The space which can be formed between the free end 18 of the guide and the grid 14 can be varied by altering the extent to which the guide 16 is attached to the net. A final attachment point at lower than 1/3 of the way down the horizontal profile will allow a larger opening.

The attachment of the guide to the net may be able to be modified if desired to allow for different sizes and types of larger animals which may be present in different locations and/or seasons.

Further, because of the force of the water, the free end of the guide is held against the body of the turtle or large fish. This reduces the likelihood of any prawns passing through the gap with the turtle. The turtle is guided downwardly by the grid in the direction of the arrows marked D towards an opening 19 in the lower portion of the net adjacent the grid. The escape opening is in the form of a funnel which directs the turtle or other animal outwardly in the direction of arrow E. When a turtle or other large animal is not passing through the opening, the water pressure will typically force the outer wall 20 of the opening funnel against the outer wall 21 of the net.

The grid 14 further includes a bracket 22 or other means for allowing a line to be attached thereto. With conventional trawling nets, the net is dragged through the water from lines attached to the forward open end. In a particularly preferred embodiment of the present invention, a line from the fishing vessel is also attached to the grid. The attachment of the grid to a line provides a lifting or pivoting action of the grid away from the sea bed. This lifting action assists turtles or the like in proceeding downwards towards the opening. A further advantage of providing a lifting means at the grid is that when the net is returned to the fishing vessel during haul back, the forward end 15 of the net collapses against the grid. This prevents or minimizes the likelihood of prawns escaping from the cod end back through the grid and the opening. With conventional nets, it is common in rough conditions for prawns to be lost during haul back, as the opening is not completely closed. Still further, this lifting action of the grid assists the cod end to be able to swing aboard the fishing vessel rather than being dragged or hauled aboard as per conventional nets. Where the grid is hauled aboard, it poses a safety hazard, as it is free to swing around and strike an operator.

.O

The section of the present invention enables turtles and large fish to escape a trawl net whilst increasing the overall yield of prawns. Loss of prawns can be reduced during both trawling and retrieval.

It will be appreciated that various modifications and changes may be made to the invention as described and claimed herein, without departing from the spirit and scope thereof.

Claims (7)

1. A section of a trawl net for prawns or other animals, the section having a leading end and a trailing grid, the grid having a plurality of bars spaced to allow prawns or other desired animals to pass therethrough, but can exclude larger animals from such passage, the section including an escape means located adjacent the grid and a guide, the guide having a forward end attached to the leading end and which can extend through the section towards the grid such that a channel is defined between the guide and an outer wall of the section and when in use, animals entering the leading end are directed through the channel towards the grid; whereby the guide has a free end which is movable between a closed position in which the free end abuts the grid and an open position, and the free end is normally maintained S:in the closed position by water pressure when the device is in use, but can be S•urged to the open position by animals or objects which enter the channel but are excluded from passing through the grid to allow the excluded animals or objects to pass between the free end of the guide and the grid towards the escape means.

2. The section of claim 1, wherein the grid is inclined towards the escape means.

3. The section of claim 2, wherein the grid is inclined at an angle of between about 300 to about 600. S* 4. The section of claim 3, wherein the angle is about 45 o The section of any one of claims 1 to 4, wherein the escape means is located at a bottom portion of the section.

6. The section of any one of claims 1 to 5, wherein the grid is a length of netting attached to opposed side walls of the leading end.

7. The section of any one of claims 1 to 6 wherein the grid includes an attachment means for attaching a retrieval line to the grid.

8. A trawl net which includes the section of any one of claims 1 to 7 and a trailing closed end such that prawns or other animals which pass through the grid are collected in the closed end.

9. A trawl net, substantially as hereinbefore described with 9 reference to the Figure. Dated this 20t day of February 2002 SVEN-AKE MICHAEL KLINGWALL By His Patent Attorneys CULLEN CO.