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)

Abstract

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.

Spatial distribution pattern of European hake, <em>Merluccius merluccius</em> (Pisces: Merlucciidae), in the Mediterranean Sea

“…This demersal species is one of the most important commercial resources for trawl and small-scale fisheries (fixed gillnets, bottom longlines) in the Mediterranean basin (STECF 2015). Trawlers mainly catch specimens below 30 cm total length, whereas bottom longlines and gillnets target adults (Sbrana et al 2007).…”

Size-dependent survival of European hake juveniles in the Mediterranean Sea

“…are less available to bottom trawl gears (thanks to spawning refugia; Colloca et al 2013, Caddy 2015 and references therein), although they are targeted by other commercial gears such as longlines and gillnets in some Mediterranean areas (Aldebert et al 1993, Sbrana et al 2007. All of these findings evidence the high importance of having a complete view of the juvenile life stage to understand how the combination of ecological, environmental and fishing impact shapes natural mortality (Jørgensen et al 2013), a key population dynamics parameter normally assumed to be constant and age-independent in the assessment frameworks (Abella et al 1997, Caddy 2015.…”

Gillnet selectivity for non target fish species caught by red mullet gillnets north Aegean Sea

“…Gillnets are commonly used fishing gears in the Mediterranean Sea ( Martin et al, 1999;Papaconstantinou and Farrugio, 2000;Sbrana et al, 2007;Karakulak and Erk, 2008;Ayaz et al, 2010b) that known as multi species fishing field. Discard rate was calculated as 15% by Kelleher (2005) around Mediterranean and Black Sea, whereas 58% (Ayaz et al, 2010a), 56% (Aydın et al, 2008) and 77.4% -81.4% (Aydın et al 2013) in red mullet gill nets Turkish coasts of the Aegean Sea.…”