Effect of codend mesh size increases on the size selectivity of commercial species in a small mesh bottom trawl fishery

2013 ◽  
Vol 29 (4) ◽  
pp. 762-768 ◽  
Author(s):  
H. P. Nguyen ◽  
R. B. Larsen
Keyword(s):  
Mesh Size ◽  
Bottom Trawl ◽  
Size Selectivity ◽  
Trawl Fishery ◽  
Commercial Species

scholarly journals Estimating selectivity of experimental diamond (T0) and turned mesh (T90) codends in multi-species Mediterranean bottom trawl

2020 ◽  
Author(s):  
ANDREA PETETTA ◽  
BENT HERRMANN ◽  
MASSIMO VIRGILI ◽  
ROCCO De MARCO ◽  
GIOVANNI CANDUCI ◽  
...  
Keyword(s):  
Mesh Size ◽  
Bottom Trawl ◽  
Size Selectivity ◽  
Important Species ◽  
Trawl Fishery ◽  
The North ◽  
Common Squid ◽  
Commercially Important ◽  
The Mediterranean ◽  
The Difference

The effect of shifting from a diamond mesh codend (T0) to a 90° turned mesh codend (T90) on the size selectivity of seven commercially important species in the Mediterranean bottom trawl fishery was evaluated. During sea trials conducted in the north-western Adriatic, two experimental codends made of 54 mm nominal mesh size netting that differed only in mesh configuration were alternately mounted on the same trawl. Overall, the size selectivity was significantly improved for all the species analysed, shifting from T0 to T90. The difference in the average expected L50values between T90 and T0 was particularly marked in European hake (Merluccius merluccius, 21.26 vs 11.26 cm total length), common squid (Loligo vulgaris, 12.06 vs 7.88 cm mantle length) and mantis shrimp (Squilla mantis, 20.78 vs 13.35 mm carapace length). Both codends had an excessive size selectivity especially for red mullet (Mullus barbatus), Mediterranean horse mackerel (Trachurus mediterraneus) and whiting (Merlangius merlangus), thus involving a commercial loss. These findings demonstrate the efficiency of the T90 codend tested at excluding undersized specimens, especially of hake, whose average L50was above the minimum conservation reference size of 20 cm. The adoption of this practical and inexpensive solution could help improve the management of the demersal resources targeted by the Mediterranean bottom trawl fishery.

scholarly journals Effect of a quality-improving cod end on size selectivity and catch patterns of cod in bottom trawl fishery

2019 ◽  
Vol 76 (11) ◽  
pp. 2110-2120 ◽  
Author(s):  
Jesse Brinkhof ◽  
Bent Herrmann ◽  
Roger B. Larsen ◽  
Tiago Veiga-Malta
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Relative Size ◽  
Bottom Trawl ◽  
Size Selectivity ◽  
Total Size ◽  
Trawl Fishery ◽  
The Barents Sea ◽  
Sea Bottom ◽  
Significant Difference

A new cod-end concept developed and tested exhibited significantly improved quality of caught cod (Gadus morhua) compared with that of the conventional cod end used in the Barents Sea bottom trawl fishery. However, the design of the new quality-improving cod end raised concerns about its size selectivity and the possibility that higher retention probability could negatively impact the catch pattern by increasing the proportion of undersized cod. Therefore, the goal of this study was to quantify and compare the size selectivity and catch pattern for cod when deploying, respectively, the conventional and new quality-improving cod end in the Barents Sea bottom trawl fishery. The new quality-improving cod end had significantly lower relative size selectivity than the conventional cod end, but no significant difference in the catch patterns was detected in the trawl. Further, estimation of the total size selectivity in the trawl revealed that the increased retention of small cod when using the quality-improving cod end was minor. Hence, despite the reduced selectivity, the quality-improving cod end can be used with low risk of retaining small cod.

scholarly journals Using vertical distribution to separate fish from crustaceans in a mixed species trawl fishery

2019 ◽  
Vol 76 (10) ◽  
pp. 1781-1794 ◽  
Author(s):  
Junita Diana Karlsen ◽  
Ludvig Ahm Krag ◽  
Bent Herrmann ◽  
Henrik Skaarup Lund
Keyword(s):  
Vertical Distribution ◽  
Separation Efficiency ◽  
Fishing Gear ◽  
Relative Height ◽  
Size Selectivity ◽  
Mixed Species ◽  
Nephrops Norvegicus ◽  
Trawl Fishery ◽  
Successful Separation ◽  
Commercial Species

A major challenge in mixed fisheries is achieving acceptable size selectivity for morphologically different species using the same fishing gear. Separator trawls can have different selective properties in the upper and lower compartments and provide successful separation of species. We used a horizontally divided codend with small square meshes (40 mm) and a simple frame to stimulate fish to swim into the upper compartment. The majority of the fish were separated successfully from Nephrops (Nephrops norvegicus), but their preference were uniform. Less than 10% of the Nephrops entered the upper compartment. Length-based analysis revealed three patterns of separation efficiency among nine commercial species: length-dependent separation and preference for the upper or lower compartments. The separation efficiency should be improved for small roundfish and flatfish. There was little diel effect on the separation efficiency. The preference of fish for a compartment, taking the relative height of that compartment into account, was established for this and similar previous studies to enable comparison of results. We recommend length-based analysis to account for the fished population when interpreting results.

scholarly journals Effect of a lateral square-mesh panel on the catch pattern and catch efficiency in a Mediterranean bottom trawl fishery

2020 ◽  
Vol 21 (1) ◽  
pp. 105
Author(s):  
SARA BONANOMI ◽  
JURE BRČIĆ ◽  
BENT HERRMANN ◽  
EMILIO NOTTI ◽  
ALESSANDRO COLOMBELLI ◽  
...  
Keyword(s):  
Mesh Size ◽  
Lateral Position ◽  
Bottom Trawl ◽  
Important Species ◽  
Commercial Fish ◽  
Trawl Fishery ◽  
Red Mullet ◽  
Commercially Important ◽  
The Mediterranean ◽  
Trawl Fisheries

The current legal codends used in Mediterranean bottom trawl fisheries are at high risk of retaining undersized individuals of several commercial fish species. This entails that codends alone are unable to provide the desired exploitation pattern. A simple technological measure that potentially can provide higher release efficiency of undersized fish are Square-Mesh Panels (SMPs). SMPs are often applied in the upper section of the trawl belly, just ahead the codend. However, recent studies in the Mediterranean have demonstrated that SMPs mounted in this position provided limited release efficiency, because very few fish came into contact with their meshes. In attempt to improve SMPs efficiency in the Mediterranean bottom trawl fisheries, we applied them on the lateral sides of the last tapered section of the trawl belly, just ahead of the codend, and fitted two guiding panels in the trawl belly to enhance fish-SMP contact. We compared the catch performance of a standard commercial trawl with a 52 mm diamond-mesh codend and of a similar trawl fitted with lateral SMPs (70 mm mesh size) in the belly using a twin trawl. The study focused on red mullet (Mullus barbatus), a commercially important species, but data for gurnard (Chelidonichthys lucerna and Chelidonichthys cuculus)  were also obtained and analysed. In contrast to previous research on SMPs mounted in the top panel of the trawl, in this study SMPs induced a significant effect on catch performance for red mullet, demonstrating that their lateral position involved greater fish-SMP contact. However, since the test trawl lost a significant amount of legal-sized red mullet compared with the standard trawl, the effect was not wholly positive, possibly due to an excessively large mesh size. Therefore, future studies should be encouraged to test lateral SMPs with smaller mesh sizes.

scholarly journals The influence of mesh size and shape on the size selection of European hake (Merluccius merluccius) in demersal trawl codends: An investigation based on fish morphology and simulation of mesh geometry

2018 ◽  
Vol 82 (3) ◽  
pp. 147 ◽  
Author(s):  
Adnan Tokaç ◽  
Bent Herrmann ◽  
Gökhan Gökçe ◽  
Ludvig Ahm Krag ◽  
Davud Sadegh Nezhad
Keyword(s):  
Mesh Size ◽  
Bottom Trawl ◽  
Opening Angle ◽  
Size Selectivity ◽  
Merluccius Merluccius ◽  
Size Selection ◽  
Size And Shape ◽  
Wide Range ◽  
European Hake ◽  
Selection Of

European hake (Merluccius merluccius) is an important commercial species for several European bottom trawl fisheries. Therefore, understanding the influence of codend mesh size and shape on the size selection of European hake is critical for defining technical measures for fisheries targeting this species. Based on morphology data collected on European hake, the influence of mesh size and shape on bottom trawl codend size selectivity was investigated by simulation using the FISHSELECT methodology successfully applied previously for other species. The predicted size selection for European hake was found to agree well with previous experimental results for a wide range of mesh sizes if it was assumed that the codend meshes had a relatively small opening angle, between 20° and 40°, during trawling. This study enables detailed prediction of size selectivity for European hake and offers a potential explanation for previous experimental size selectivity results.

scholarly journals Comparison of selectivity of the trawl codends for whiting (Merlangius merlangus euxinus) in the Black Sea

2019 ◽  
Vol 36 (3) ◽  
pp. 301-311 ◽  
Author(s):  
Mustafa Zengin ◽  
İlkay Özcan Akpınar ◽  
Muharrem Hakan Kaykaç ◽  
Zafer Tosunoğlu
Keyword(s):  
Black Sea ◽  
Mesh Size ◽  
Bottom Trawl ◽  
The Black Sea ◽  
Size Selectivity ◽  
Minimum Landing Size ◽  
Merlangius Merlangus ◽  
First Maturity

A large part of the total whiting (Merlangius merlangus euxinus) fishing in the Black Sea is carried out with the traditional bottom trawl nets along the coast of Turkey. Diamond mesh shape with 40 mm mesh size (40D) has been used in the codends of these trawls. In this study, the traditional trawl codend (40D) and square-mesh codend with different size (36S and 40S) were compared for whiting size selectivity in August 2014. Selectivity data were collected by using a covered codend method and analysed taking between haul variations in to account. The selectivity parameters were estimated by using CC2000 software. Results showed that commercially used 40D trawl codend is not selective enough to release immature of whiting. However, the net change in square mesh (36S and 40S) instead of a diamond-shaped (40D) mesh significantly improved the mesh selectivity for whiting. The 40S trawl codend is even higher than the first maturity size (LM50) with a length at fifty percent retention (L50) of 15.74 cm. In conclusion all square mesh codends with different mesh size tested here supplied appropriate selection considering minimum landing size (MLS) of whiting.

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