RU2483535C1 - Method to define selectivity of trawl net - Google Patents

Abstract

FIELD: agriculture.

SUBSTANCE: invention relates to commercial fishery. The method is realised by comparison of catch and readings of a hydroacoustic sonar. The hydroacoustic sonar comprises several blocks arranged on upper and lower framing ropes of the net oppositely to each other at the equal distance. The distance between blocks is calculated according to a certain dependence, based on the angular width of existing characteristics of directivity of a probing beam of a block and a value of vertical opening of the trawl net.

EFFECT: invention makes it possible to validly and in a quality manner determine selectivity of a trawl net directly in process of trawling.

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Description

The invention relates to the fishing industry, and in particular to industrial fishing, to methods for determining the selectivity of a trawl.

Known methods for determining the selectivity of fishing trawls. In a method using alternate trawling (A. Treschev, 1974. Scientific basis of selective fishing. M. Food industry, p.180-182; ICES Cooperative Report N215, 1996, Manual of methods of measuring the selectivity of towed fishing gears. Paloegade 2-4DK-1261 Copenhagen K. Denmark, p.6-7), performed from the same vessel in the same area, alternately operate trawls with different mesh sizes. The catches obtained by each trawl are analyzed and, by comparing the size-quantitative composition of the catches, the selective (selective) properties of the compared trawls are evaluated. The disadvantage of this method is the practical impossibility of assessing the actual selectivity of a particular tested or investigated trawl, but only the determination of the difference in the selectivity of this and conditionally control trawl.

The method of determining the selectivity of a trawl using parallel simultaneous trawls, when trawling is necessarily carried out from two vessels of the same type armed with the same trawls, is also characterized by similar disadvantages, as well as the complexity of the implementation (Treschev A.I., 1974. Scientific basis of selective fishing. M. Food industry t, p. 183-184; ICES Cooperative Report N215, 1996, Manual of methods of measuring the selectivity of towed fishing gears. Paloegade 2-4DK-1261 Copenhagen K. Denmark, p. 7). Upon arrival to the fishing area, both vessels simultaneously give trawls, trawl at parallel courses with a minimum distance between the vessels on command from one of the vessels. They also lift trawls aboard at the same time; catches are compared in terms of size and quantity.

There is also a method for determining the selectivity of fishing trawls based on the use of fine mesh net coatings (ICES Cooperative Report N215, 1996, Manual of methods of measuring the selectivity of towed fishing gears. Paloegade 2-4DK-1261 Copenhagen K. Denmark, p. 6). The trawl or part of it is covered with a large mesh network in such a way that the fish passing through the main network is retained in the covering network. At the end of the trawling, the catch from the trawl bag and the covering net are separately poured out and taken into account. The selectivity of this trawl is determined based on the ratio (for n trawls) of the size-quantitative composition of the fish included in the trawl equal to the size-quantitative composition of the caught fish in the trawl bag plus the size-quantitative composition of the fish in the covering net and the composition of the fish remaining in the trawl bag, t. e. (specified) catch composition. The specified method allows to obtain somewhat more reliable results on the selectivity of the studied trawl, but is significantly more difficult in practical use. In addition, due to the additional outer coating, the characteristics of the trawl itself also change, which will adversely affect the representativeness of the results of determining its selectivity.

Closest to the proposed is a method for determining the selectivity of a fishing trawl using acoustic means (volumetric acoustic density estimation, S _A ) (Somerton DA, Williams K., von Szalay PG and Rose C. S. 2011. Using acoustics to estimate the fish-length selectivity of trawl mesh. ICES Journal of Marine Science, 68: 1558-1565). The size-quantitative composition of the fish entering the mouth of the trawl (trawl) was determined using two estimates of acoustic backscattering: measurements of the vertical action of actual acoustic backscattering from fish concentrations below the vessel by echo-integration installed on board (in the hull of the vessel) through echo integration within the layer water trapped by the trawl (with a thickness equal to the vertical opening of the trawl) and the theoretical estimate of acoustic backscattering obtained s (would take place) from the fish caught, taking into account its abundance, distribution by size (length) and acoustic strength of the target TS of the fish, i.e. the ratio of TS to L is the length of the fish (which are available for a number of commercial fish). Accordingly, the selectivity of the tested trawl is evaluated (determined) based on the ratio of the size-quantitative composition of the fish included in the trawl and the size-quantitative composition of the fish in the obtained catch obtained by the indicated method. In this work (Somerton D.A. et al., 2011) it is indicated that, in comparative tests of the proposed method with the method of finely milled trawl coatings, the results of determining selectivity were similar.

It is free from the disadvantages of the above known methods, does not affect the characteristics of the trawl, however, the selectivity estimates when using it have insufficient accuracy and reliability due to the practical impossibility of integrating the signals reflected from the fish only within the area of the mouth of the trawl, due to the expansion of the front of the emitted acoustic vibrations any sonar equipment, as well as with certain assumptions when translating volumetric acoustic readings density S _A in the size-quantitative composition of the fish included in the trawl. In addition, in many situations, it is unlikely that the size and quantity composition of fish accumulations, recorded in a layer of water under the vessel, will be the same (remain unchanged) when approaching the mouth of the trawl due to the influence of the noise of the trawler, the visual reaction of the fish to the trawl warp , cables, trawl boards and due to the influence of other factors on the behavior of fish. This will also adversely affect the accuracy of the selectivity assessment.

The technical result in the implementation of the inventive method is to obtain a reliable and qualitative determination of the selectivity of the fishing trawl directly during real trawls, due to the possibility of a more accurate assessment of the size-quantitative composition of the fish included in the trawl.

The problem is achieved in a method for determining the selectivity of a fishing trawl by comparing the performance of a sonar echolocation device and obtained in the catch of this trawl, while the sonar sonar device consists of an nth number of blocks and placed on equal and upper sections of the trawl at equal intervals opposite each other, when this length of the segment L is determined based on the angular width of the current directivity α of the probe beam of the block according to the formula L = 2htgα / 2, where h is the vertical the opening of the trawl, α is the angle of the probe beam, while the sonar location of fish at the mouth of the trawl is carried out by cross-signaling.

Figure 1 shows a side view, while working at sea.

To implement the method, the figure shows the trawl 1, upper 2 and lower 3 rebounds, sonar sonar device 4, consisting of the n-th number of blocks (4 ₁ , 4 ₂ ... 4 _{n / 2} , 4 _{n / 2 + 1} , 4 _{n / 2 + 2} , ... 4 _n ), and trawler 5.

Two equal groups of blocks of sonar sonar device 4 are located at equal distances at the top 2 and bottom 3 of the selection of the trawl 1. All blocks have identification numbers, 4 ₁ , 4 ₂ ... 4 _{n / 2} for the top selection and 4 _{n / 2 + 1} , 4 _{n / 2 + 2} ... 4 _n for the bottom. Each of the blocks of the top pick group is located opposite the corresponding block of the bottom pick (by numbers, i.e. 4 ₁ opposite 4 _{n / 2 + 1} , 4 ₂ opposite 4 _{n / 2 + 2} ... 4 _{n / 2} opposite 4n) to provide acoustic overlapping by the indicated pairs of blocks of the corresponding observation zone in connection with a certain taper of their directivity characteristics. When the trawl 5 moves, the space of its mouth is blocked by hydroacoustic rays from each of the groups of echolocation blocks towards each other.

Work on the proposed method is as follows. After the vessel arrives in the fishing area, before starting the trawl selectivity check, one group of sonar blocks 4 is installed on the top 2, the other on the bottom 3 selection of the trawl, while the sonar blocks 4 in each group are equal. Blocks 4 are placed on equal segments opposite each other, while the length of the segment L is determined based on the angular width of the current directivity α of the probe beam of the block according to the formula L = 2htgα / 2, where h is the vertical opening of the trawl, α is the angle of the probe beam, while sonar location of fish at the mouth of the trawl is carried out by cross-signaling.

Sonar blocks 4 of the upper 2 selections are connected to each other using communication cables (not shown in Fig.) And this group is connected to the cable communication line with the vessel. After the return of the trawl 1, all blocks 4 will be in standby mode, i.e. their electronic circuits will be powered by their own batteries using their own pressure sensors. Then, according to the triggering code signal from the vessel, the leading echo-location unit of the top 2 rebound group, set at one of its edges, starts at number 4 ₁ . It emits a probe pulse in the direction of the corresponding block 4 _{n / 2 + 1 of the} bottom 3 rebounds, receives and stores (stores) the signals reflected from the fish. When this probe pulse arrives at block 4 _{n / 2 + 1 of the} group of the bottom 3 rebounds, it is highlighted by this block and radiation is triggered towards the top 2 rebounds of the probe pulse of the block 4 _{n / 2 + 1} groups of the bottom 3 rebounds. The indicated block begins to receive and store echo signals from fish from a given section of the mouth of the trawl 1. When a probe pulse of block 4 _{n / 2 + 1} groups of the lower 3 rebounds is received by block 4 ₁ of the upper 2 rebounds, the receiving path of this block is closed and a code signal is sent from it to the block of the group of the upper 2 rebounds installed in its middle part. The separation in distance of the launches of the echolocation blocks 4 is provided to exclude any acoustic influence of them on each other. Upon receipt of the probe pulse of the block 4 _{n / 2 + 1} groups of the lower rebounds reflected from the upper 2 rebounds of the trawl, the receiving path of the block 4 _{n / 2 + 1} groups of the lower 3 rebounds closes. According to the code signal from block 4 ₁ of the upper 2 rebounds group, received by the upper 2 rebounds group block installed in the middle of the upper 2 rebounds, this block emits a probe pulse in the direction of the corresponding block of the lower 3 rebounds group. These blocks work similarly to blocks 4 ₁ and 4 _{n / 2 + 1} .... Upon receipt of the probe pulse of the middle block of the group of the lower 3 rebounds by the middle block of the group of the upper 2 rebounds, the receiving path of this block is closed and a code signal is sent from it to the block 4 of the ₂ groups of the upper rebounds, which works similarly to block 4 ₁ . Next, from the block 4 ₂ groups of the upper 2 rebounds, a code signal is sent to start the block of the group of the upper 2 rebounds, installed next to the middle block of this group, in the direction of its last extreme block 4 _{n / 2} , etc. After the start and completion of one operation cycle of the last (second extreme) sonar unit 4 _{n / 2} of the upper 2 rebound group, a code signal is sent from it (similar to that transmitted from the ship) to restart the block 4 ₁ of the upper 2 rebound group and a new (second) one begins the period of operation of the echolocation blocks of the upper 2 and lower 3 rebounds. The result is a consistent scoring of the entire area of the mouth of the trawl 1, the reception and storage of echo signals from fish from this zone. Due to the relatively high speed of propagation of acoustic vibrations in the aquatic environment and the relatively small distances between the upper 2 and lower 3 selections, with a vertical opening of the trawl of 50 m, the number of echolocation blocks in the group equal to 10, and α≈23 °, the entire area of the mouth of the trawl 1 will be covered in a time equal to approximately 2/3 s (namely, at a speed of sound of 1500 m / s and a total distance traveled by sound at 10 blocks, and a passage distance for one block equal to 50 × 2 = 100 m, the total time will be equal to 1000/1500, i.e. 2/3 s). Received echoes are stored and stored in each block. Immediately after the start of hauling (raising) of the trawl from the side of the vessel, a signal is sent to turn off the sonar blocks.

After lifting the trawl 1 on board the trawler, the size and quantity composition of the fish caught by the trawl is calculated. Blocks 4 of sonar echolocation equipment are removed and the acoustic information stored in them - echograms - is read for subsequent processing. As a result, electronic echograms of echolocation blocks 4 obtained during the trawling will be presented. Using well-known computer programs used in marine scientific research fishing equipment and used in conventional sonar surveys, for example, in EK-60 by Simrad, Ehovu and others, the values of volumetric acoustic density, S _A , histograms of size distribution and, accordingly, size-quantitative composition of fish that passed into the trawl 1. If necessary, refinements are made according to the received echograms. Based on the ratio of the size-quantitative composition of the fish included in the trawl and the size-quantitative composition of the fish in the obtained catch, the selectivity of the tested trawl is determined.

As a result, by determining the volumetric acoustic density S _{A of the} fish directly at the mouth of the trawl and the direct (direct) acoustic assessment of the size composition of fish passing into the trawl (at the mouth of the trawl), the accuracy and reliability of determining the selectivity of the trawl are improved.

Claims (1)

A method for determining the selectivity of a fishing trawl by comparing the indicators of a sonar echolocation device and the trawl obtained in the catch, characterized in that the sonar sonar device consists of an nth number of blocks placed on the upper and lower selections of the trawl in equal sections opposite each other, while the length of the segment L is determined based on the angular width of the current directivity α of the probe beam of the block according to the formula L = 2htgα / 2, where h is the vertical opening of the trawl, α is the probing beam, the sonar of locating the fish in the mouth of the trawl is carried out by cross-flow signal.