Selectivity of diamond and square mesh cod ends for horse mackerel (<i>Trachurus trachurus</i>), European hake (<i>Merluccius merluccius</i>) and axillary seabream (<i>Pagellus acarne</i>) in the shallow groundfish assemblage off the south-west coast of Portugal

Abstract

2003Selectivity of diamond and square mesh cod ends for horse mackerel (Trachurus trachurus), European hake (Merluccius merluccius) and axillary seabream (Pagellus acarne) in the shallow groundfish assemblage off the south-west coast of Portugal* AIDA CAMPOS and PAULO FONSECA IPIMAR, Avenida de Brasília, 1449-006, Lisbon, Portugal. E-mail: acampos@ipimar.pt SUMMARY: The effects of an increase in cod end mesh size from 65 to 70 and 80 mm and a change of mesh configuration from 65 mm diamond to 65 mm square mesh on the size selectivity of horse mackerel (Trachurus trachurus), hake (Merluccius merluccius) and axillary seabream (Pagellus acarne) of the shallow groundfish assemblage off the Portuguese southwest coast were evaluated. The increase in mesh size had a small but significant effect on size selectivity for the three species, while the change in mesh configuration led to a much more pronounced increase in the selectivity parameters. For horse mackerel, the L 50 estimates ranged from 14.4 to 16.0 cm in the diamond mesh cod ends-values that are close to the minimum landing size of 15 cm. For hake, L 50 of 17.0 and 18.3 cm were estimated for the 70 and 80 mm diamond cod ends respectively, while for the axillary seabream the L 50 estimated was 13.9 cm for the 80 mm diamond mesh cod end. These values are well below the minimum landing sizes of 27 and 18 cm for these species. The corresponding estimates in the square mesh cod end were 21.9, 32.4 and 19.6 cm, with the loss of a high percentage (76%) of horse mackerel above the minimum landing size. For all the cod ends tested, the observed retention was presented as a function of maximum girth/mesh perimeter, which allowed a better understanding of the selection process for the species in study. Selectivity estimates for horse mackerel and hake were also compared to those obtained by Campos et al. (2003) for the same species in 1993 off the south coast, where they are captured as a by-catch in the crustacean fishery.Key words: cod end selectivity, mesh size, mesh configuration, length-girth relationships, by-catch, Trachurus trachurus, Merluccius merluccius, Pagellus acarne. RESUMEN: SELECTIVIDAD DE COPOS CON MALLA DE DIAMANTE Y CUADRADA PARA JUREL (TRACHURUS TRACHURUS), MERLUZA EUROPEA (MERLUCCIUS MERLUCCIUS) Y ALIGOTE (PAGELLUS ACARNE) EN LOS POBLAMIENTOS DE PECES DEMERSALES DE AGUAS SOMERAS FRENTE A LAS COSTAS DEL SUROESTE DEPORTUGAL. -Los efectos de un incremento en la dimensión de la malla del copo desde 65 a 70 y 80 mm, así como un cambio en su configuración entre malla de diamante de 65 mm y malla cuadrada de 65 mm han sido evaluados sobre la selectividad por talla del arte de arrastre para jurel (Trachurus trachurus), merluza europea (Merluccius merluccius) y aligote (Pagellus acarne) en los poblamientos de peces demersales de aguas someras frente a la costa del suroeste de Portugal. El incremento del tamaño de la malla ha tenido un efecto pequeño pero significativo sobre la selectividad por tamaños de las tres especies, mientras que el cambio de la configu...

Codend selectivity for jack mackerel and whitefin jack and unequal split parameter estimates observed in trouser trawl experiments

“…This suggests that there was an insufficient sieving effect of the mesh on jack mackerel with girths that were small enough to pass through the mesh in this study. Previous studies [33][34][35][36][37][38][39] have reported that the selection factor of diamond mesh codend for Trachurus fish varies from 2.0 to 3.43, and that of square mesh codend varies from 3.4 to 4.3, based on the measurement of the total length of the fish ( Table 4). The l 50 in fork length for the jack mackerel Trachurus japonicus estimated in this study corresponded to the l 50 in total length of 12.95 cm with the regression equation in Eq.…”

Gillnet selectivity in the Ebro Delta coastal lagoons and its implication for the fishery management of the sand smelt, Atherina boyeri (Actinopterygii: Atherinidae)

“…No common pattern for the best fit was found between different species; thus suggesting that each fish or group of fish were caught differently depending on its body shape (Fonseca et al, 2005) and its differences in behavior towards the fishing gear (Campos and Fonseca, 2003). In general, Gamma was the best fit when having higher number of captures,…”

“…As said by Campos and Fonseca (2003) the management of a species fishery based simply on mesh size regulation is very difficult, but is the first step to improve an uncontrolled fishing situation.…”

The effects of subsampling and between haul variation on the size selectivity estimation of Chilean hake (Merluccius gayi gayi)

“…Chilean hake: Saetersdal & Villegas (1968); Arana (1970); Gálvez & Rebolledo (2005). European hake: Campos & Fonseca (2003); Campos et al (2003aCampos et al ( , 2003b; Deval et al (2007);Lucchetti (2008); Sala & Lucchetti (2010); Tokaç et al (2010). Argentine hake: Rojo & Silvosa (1970); Verazay et al (1992).…”