Gill-net selectivity off the Portuguese western coast

Fonseca, Paulo; Martins, Rogélia; Campos, Aida; Sobral, Preciosa

doi:10.1016/j.fishres.2005.01.015

Cited by 42 publications

(28 citation statements)

References 27 publications

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“…The modal lengths reported for this mesh size by Santos et al (2003) and Fonseca et al (2005) were 40.1 and 40.3 respectively, which were slightly lower than those obtained in the present study, probably because entangled fish were not taken into account in the analyses.…”

Section: Discussioncontrasting

confidence: 86%

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Comparison of the catches of European hake (Merluccius merluccius, L. 1758) taken with experimental gillnets of different mesh sizes in the northern Tyrrhenian Sea (western Mediterranean)

Sbrana¹,

Belcari²,

Ranieri³

et al. 2007

Sci. Mar.

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SUMMARY: The impact of the gillnet fishery on Merluccius merluccius (European hake) was investigated in the northern Tyrrhenian Sea, western Mediterranean. Four mesh sizes were tested: 53, 62.5, 70 and 82 mm. Horse mackerel (Trachurus trachurus), hake and tub gurnard (Chelidonichthys lucerna) dominated the catches, from a minimum of 89% (82 mm mesh) to a maximum of 97.8% (70 mm) of the biomass caught. Efficiency of the four meshes was not significantly different with respect to the total hake catches. Selectivity on M. merluccius was assessed by Sechin and SELECT methods. Tangling was an important catch modality for hake, as evidenced by the results of the Sechin model which described only the first mode of the size distributions corresponding to the entangled specimens. SELECT showed that the bi-modal function gave the best adjustment to the length-frequency distributions; the modal catch sizes were 33, 39.2, 43.6 and 51 cm total length respectively for the 53, 62.5, 70 and 82 mm mesh sizes. Taking into account the size of first maturity for females (35.1 cm TL), 62.5 mm is the most adequate mesh for exploiting hake as it gives some protection to both immature specimens and large females.Keywords: European hake, gillnet, selectivity, Sechin method, SELECT method, western Mediterranean, artisanal fishery. RESUMEN: COMPARACIÓN DE LAS CAPTURAS DE MERLUZA (MERLUCCIUS MERLUCCIUS, L. 1758) OBTENIDAS CON REDES EXPE-RIMENTALES DE ENMALLE DE DIFERENTES TIPOS DE MALLA, EN EL NORTE DEL MAR TIRRENO (MEDITERRÁNEO NOROCCIDENTAL).-Se estudió el impacto de la pesquería con redes de enmalle sobre la merluza, Merluccius merluccius, (merluza europea) en el norte del mar Tirreno, Mediterráneo noroccidental. Se utilizaron cuatro tamaños de malla: 53, 62.5, 70 y 82 mm. Los peces Trachurus trachurus, M. merluccius y Chelidonichthys lucerna dominaron la biomasa capturada, con un mínimo del 89% (malla de 82 mm) y un máximo del 97.8% (malla de 70 mm). La eficiencia de las cuatro mallas no resultó estadísticamente diferente. La selectividad sobre M. merluccius fue estudiada con los métodos Sechin y SELECT. El enredamiento resultó una importante manera de captura, como evidenció el método Sechin, con un buen ajuste sólo para la primera moda de las distribuciones de talla, correspondiente a ejemplares capturados por enmalle. Con el modelo SELECT la función bimodal fue la mejor para describir las estructuras de talla; las tallas modales de captura fueron 33, 39.2, 43.6 y 51 cm de longitud total, para las mallas de 53, 62.5, 70 y 82 mm respectivamente. Teniendo en cuenta la talla de primera madurez, la malla de 62.5 mm es probablemente la más adecuada para la explotación de la merluza, permitiendo una cierta protección tanto de los inmaduros como de las hembras grandes.Palabras clave: merluza, redes de enmalle, selectividad, método Sechin, método SELECT, Mediterráneo noroccidental, pesca artesanal.

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Section: Discussioncontrasting

confidence: 86%

“…The gillnet hake selectivity explained by a bi-modal curve is confirmed by other studies carried out in the Gulf of Lyons (Sacchi, 2001) and along the Portuguese coasts (Santos et al, 2003;Fonseca et al, 2005).…”

Section: Discussionsupporting

confidence: 83%

Comparison of the catches of European hake (Merluccius merluccius, L. 1758) taken with experimental gillnets of different mesh sizes in the northern Tyrrhenian Sea (western Mediterranean)

Sbrana¹,

Belcari²,

Ranieri³

et al. 2007

Sci. Mar.

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“…Fonseca et al (2005), through experimental gillnet fishing off the western coast of Portugal, have shown that management of multi-species fisheries, based only on mesh size would be difficult because optimal mesh size varies considerably among the target species. Fonseca et al (2005) also stated that in addition to mesh size, a number of technical characteristics related to gear construction such as hanging ratio have some influences on the catch size distribution. Colour of twine (Tweddle and Bodington 1988) and twine thickness (Holst et al 2002) are other technical characteristics of gillnets which influence their selectivity.…”

Section: Introductionmentioning

confidence: 99%

Length-based stock assessment of Oreochromis mossambicus and Oreochromis niloticus (Actinopterygii: Perciformes: Cichlidae) in multi-mesh gillnet fisheries in reservoirs of Sri Lanka

Amarasinghe¹,

Jayasinghe²,

Moreau³

2017

Acta Ichthyol. Piscat.

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Amarasinghe U.S., Jayasinghe R.P.P.K., Moreau J. 2017. Length-based stock assessment of Oreochromis mossambicus and Oreochromis niloticus (Actinopterygii: Perciformes: Cichlidae) in multi-mesh gillnet fisheries in reservoirs of Sri Lanka. Acta Ichthyol. Piscat. 47 (3): 265-277.Background. Gillnets of mesh sizes (6.9 to 12.7 cm) are used in individual boats in Sri Lankan reservoirs targeting exotic cichlid species, Oreochromis mossambicus (Peters, 1852) and Oreochromis niloticus (Linnaeus, 1758), which dominate the fisheries. The mesh composition of gillnets varies from boat to boat and from season to season making catch samples in individual boats are under the influence of different selectivity patterns. As such, the conventional procedure of correcting length frequency samples using the overall mean selectivity pattern in the fishery is not precise in estimating growth parameters. The presently reported study aimed at assessing cichlid stocks in three tropical reservoirs accounting for gillnet selectivity of individual sampled boats. Material and methods. Length frequency data obtained from each boat were corrected for the combined selectivity of the fleet of gillnets of different mesh sizes used in the boat during the sampling occasion. For predicting optimal fishing strategies using a yield-per-recruit approach, probabilities of capture determined from the array of fishing mortality in the length-structured virtual population analysis was incorporated.Results. Length frequency data corrected for overall gillnet selectivity in sampled boats gave reliable estimates of von Bertalanffy growth parameters. Based on these estimates, mortality parameters were determined and the overall gear selection pattern was deduced from the array of fishing mortality in the length-structured virtual population analysis. Optimal fishing strategies were determined incorporating overall probabilities of capture in the relative yield-per-recruit (Y′ × R -1 ) analysis. Conclusion. The overall gillnet selection pattern of a sampled boat offers a methodology for reliable estimation of growth parameters. Although both cichlid species are caught in gillnets simultaneously, Y′ × R -1 analyses predicted increase of exploitation rate for one species while its decrease for the other species perhaps due to influence of other factors such as fish behaviour and fishers' choice of specific areas for fishing. This analysis provides a methodology of a more precise length-based stock assessment in future research.

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“…The possibility of catching by tangling is increasing by the decreased hanging ratio of gillnets (Karlsen and Bjarnason, 1986). The studies on selectivity have mostly emphasized the effect of mesh size on the selectivity of species (Petrakis and Stergiou, 1996;Psuty and Borowski, 1997;Santos et al, 1998;Madsen et al, 1999;Fujimori and Tokai, 2001;Fabi et al, 2002;Özekinci et al, 2003;Park et al, 2004;Fonseca et al, 2005;Dinçer and Bahar, 2008;Karakulak and Erk, 2008;Acarlı et al, 2013). The mesh size is detected as the main factor that affects the selectivity (Von Brandt, 1975).…”

Section: Introductionmentioning

confidence: 99%

Untitled

Hall¹

2015

Turk. J. Fish. Aquat. Sci.

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This study was conducted between November 2011 -January 2013 on Bogue gill nets in mesh size of 36, 40, 44 and 50 mm targeting bogue (Boops boops, L. 1758), which is used in commercial fishing commonly at Çanakkale shores. The bouge nets were rigged in three varying hanging ratios (E=0.40, E=0.50, E=0.60) with the purpose of determining the effect of hanging ratio to selectivity. SELECT (Share Each Lengthclass Catch Total) method was used to fit selectivity curves. Lognormal model gave the best fit for selectivity curve of bogue selection according to the findings obtained from five different curve models (normal location, normal scale, gamma, lognormal, bimodal). According to the lognormal method modal lengths of bogue nets in mesh size of 36, 40, 44 and 50 mm, following findings were obtained; in hanging ratio of 0.4, rigged nets are 18.65, 20.72, 22.80 and 25.90 cm, respectively; in hanging ratio of 0.5, rigged nets are 17.90, 19.89, 21.88 and 24.86 cm, respectively; in hanging ratio of 0.6, rigged nets are 16.98, 18.87, 20.75 and 23.58 cm, respectively. Model lengths of bogue nets that were used in field studies are quite higher than the first reproduction length. The results show that the nets used in research have no pressure on bogue stock. It was determined that the hanging ratio may affects the selectivity with the help of other factors. It is taken into account the hanging ratio together with the other factors affect the selectivity.Keywords: SELECT, hanging ratio, Çanakkale, gillnet, selectivity, bogue. Kupez (Boops

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Gill-net selectivity off the Portuguese western coast

Cited by 42 publications

References 27 publications

Comparison of the catches of European hake (Merluccius merluccius, L. 1758) taken with experimental gillnets of different mesh sizes in the northern Tyrrhenian Sea (western Mediterranean)

Comparison of the catches of European hake (Merluccius merluccius, L. 1758) taken with experimental gillnets of different mesh sizes in the northern Tyrrhenian Sea (western Mediterranean)

Length-based stock assessment of Oreochromis mossambicus and Oreochromis niloticus (Actinopterygii: Perciformes: Cichlidae) in multi-mesh gillnet fisheries in reservoirs of Sri Lanka

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