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 Can a square-mesh panel inserted in front of the cod end improve size and species selectivity in Mediterranean trawl fisheries?

2018 ◽  
Vol 75 (5) ◽  
pp. 704-713 ◽  
Author(s):  
Jure Brčić ◽  
Bent Herrmann ◽  
Antonello Sala
Keyword(s):  
Deep Water ◽  
Bottom Trawl ◽  
Horse Mackerel ◽  
Trachurus Trachurus ◽  
Merluccius Merluccius ◽  
Low Probability ◽  
Low Efficiency ◽  
Trawl Fisheries ◽  
European Hake ◽  
Atlantic Horse Mackerel

An experiment was conducted to assess the selectivity in a typical Mediterranean bottom trawl, equipped with a square-mesh panel inserted in front of the cod end, for Atlantic horse mackerel (Trachurus trachurus), European hake (Merluccius merluccius), red mullet (Mullus barbatus), poor cod (Trisopterus minutus), broadtail shortfin squid (Illex coindetii), and deep-water rose shrimp (Parapaeneus longirostris). The release efficiency of undersized individuals through the panel was low. The differences in selectivity between the gear with and without the panel were very small. The low release efficiency of the square-mesh panel was caused by the lack of fish contact with the panel as they drifted towards the cod end, since the average contact probability was estimated not to exceed 9% for any of the species investigated. A low probability of contact with the selection device was thus found to be the reason for the low efficiency of the square-mesh panel.

Size selection of Atlantic cod, haddock and pollock (saithe) by otter trawls with square and diamond mesh codends of 130–155mm mesh size

1999 ◽  
Vol 41 (3) ◽  
pp. 255-271 ◽  
Author(s):  
R.G. Halliday ◽  
C.G. Cooper ◽  
P. Fanning ◽  
W.M. Hickey ◽  
P. Gagnon
Keyword(s):  
Atlantic Cod ◽  
Mesh Size ◽  
Size Selection ◽  
Selection Of

Population effects and changes in life history traits in relation to phase transitions induced by long-term fishery harvesting: European hake (Merluccius merluccius) off the Balearic Islands

2009 ◽  
Vol 66 (8) ◽  
pp. 1355-1370 ◽  
Author(s):  
Manuel Hidalgo ◽  
Enric Massutí ◽  
Beatriz Guijarro ◽  
Joan Moranta ◽  
Lorenzo Ciannelli ◽  
...  
Keyword(s):  
Life History ◽  
Life History Traits ◽  
Size Structure ◽  
Sharp Decrease ◽  
Mesh Size ◽  
Population Level ◽  
Balearic Islands ◽  
Catch Per Unit Effort ◽  
Merluccius Merluccius ◽  
European Hake

In 1980 and 1995, the European hake ( Merluccius merluccius ) population off the Balearic Islands (northwestern Mediterranean) underwent changes at both the individual level and the population level. There was a sharp decrease in abundance that coincided with a change in the seasonal catch-per-unit-effort pattern in 1980. A new population scenario emerged after 1980 characterized by an increase in the intrinsic growth rate and a decrease in carrying capacity; however, catchability remained the same. An age-structure truncation could have caused these changes, making the population more dependent on year-to-year recruitment. A change in size structure also occurred in 1995, which was evidenced by a sudden decrease in the mean length-at-age (L) and abundance of recruits and a change in the density-dependent effect on recruits. As the Mediterranean trawl fishery mainly harvests recruits and juveniles and fishery harvesting induces adaptive changes in life history traits, the sharp decrease in L of recruits could be explained as a growth reduction due to the selective pressure to stay under mesh size for longer and thus maximize survival until reproduction. These individual and population transitions explain the changes in the response to the environmental forcing observed in the European hake off the Balearic Islands.

Effects of season and mesh size on the selection of narrow-barred Spanish mackerel, Scomberomorus commerson in the Persian Gulf artisanal gillnet fishery

2021 ◽  
pp. 1-5
Author(s):  
Mojtaba Pouladi ◽  
Seyed Yousef Paighambari ◽  
Matt K. Broadhurst ◽  
Russell B. Millar ◽  
Morteza Eighani
Keyword(s):  
Relative Size ◽  
Mesh Size ◽  
Early Summer ◽  
Size Selection ◽  
Spanish Mackerel ◽  
Stock Biomass ◽  
Scomberomorus Commerson ◽  
Mean Size ◽  
The Persian Gulf ◽  
Selection Of

Abstract In response to perceived, but unknown variation among the size selection of narrow-barred Spanish mackerel (Scomberomorus commerson) by artisanal gillnetters off Iran, and the need for such data to control exploitation as a precursor to balanced harvesting, the effects of two common mesh sizes (130 and 140 mm stretched mesh opening made from multifilament twine) on catches were investigated over one fishing year (nine months encompassing autumn to spring). Both mesh sizes mostly caught S. commerson at fork lengths (FL) larger than mean sizes at maturity (>67 cm), with the mean size selection incrementally increasing in the 130-mm mesh gillnet from autumn, and especially during spring. The greater selection occurred concurrent with an increasing condition factor (CF) among S. commerson, which typically spawn in late spring/early summer. Conversely, the relative size-selection of the 140-mm mesh gillnet decreased in spring, attributed to increasing CF precluding the capture of larger fish. Such seasonal variation in size selection might be countered by increasing mesh size to ~145 or 150 mm in spring. However, the existing 140-mm mesh might positively affect stock biomass by allowing larger, more fecund fish to avoid capture during spawning. The data support the strong influence of biological and environmental factors on gillnet size selection, which might also extend to other migratory, pelagic species.

scholarly journals Release efficiency and selectivity of four different square mesh panel configurations in the Basque mixed bottom trawl fishery

2020 ◽  
Vol 84 (1) ◽  
pp. 39
Author(s):  
Elsa Cuende ◽  
Luis Arregi ◽  
Bent Herrmann ◽  
Manu Sistiaga ◽  
Mikel Basterretxea
Keyword(s):  
Bottom Trawl ◽  
Significant Positive Effect ◽  
Merluccius Merluccius ◽  
Panel Size ◽  
Blue Whiting ◽  
Size Selection ◽  
Trawl Fishery ◽  
Led Lights ◽  
Positive Effect

Reduction of discards from the Basque mixed bottom trawl fishery is a challenge. To improve the selective properties of the gear used by the fleet and supplement codend size selection, a square mesh panel (SMP) installed in the upper panel of the trawl was introduced in 2006. However, recent studies have shown that the release efficiency of this SMP is low due to lack of contact between the fish and the SMP. In this study, we tested the release efficiency of the SMP for four different gear configurations. We tested the effect of adding LED lights at two different positions and altering panel size and panel position in the trawl. The analyses were focused on two species: hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou). The results showed that the position of LED lights did not significantly affect the SMP’s release efficiency for any species. However, increasing panel size had a significant positive effect on the release efficiency of blue whiting, and placing the SMP in the lower panel improved the release efficiency of hake. These results highlight the challenge of simultaneously improving the selective properties of gear for species with different behaviour, especially in mixed demersal fisheries.

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