Summary: Sorting grids have been tested worldwide in trawl fisheries. Here we report upon the first trials performed using Nordmøre sorting grids with four different bar spacings in the trawl fisheries of the Gulf of Cadiz targeting crustaceans as the main resource. A total of 288 valid hauls and 67 commercial species were caught. Escapement and escape size selectivity were evaluated for the most important target and by-catch species. A decrease in the percentage of biomass escape was recorded with increasing grid spacing for the two target species, deep-water rose shrimp (Parapenaeus longirostris) and Norway lobster (Nephrops norvegicus), from 24% to 8% for the former and from 86 to 9% for the latter, with a 15-mm and 30-mm grid respectively. In general, high escape rates were found for most finfish and cephalopods. For hake (Merluccius merluccius), as the main by-catch species, the results showed an escape rate decreasing from 96% to 71% as the bar spacing increased. Our findings suggest the 30-mm grid would be effective for the deep-water crustacean trawlers but different mitigation measures will be required for other métiers in the multispecies trawl fishery of the Gulf of Cadiz.Keywords: by-catch; Gulf of Cadiz; deep-water rose shrimp; Nordmøre grids; selectivity; trawl fisheries. Uso de rejillas separadoras Nordmøre sobre especies objetivo y accesorias de la flota de arrastre de fondo del Golfo de CádizResumen: Las rejillas o grillas separadoras han sido testadas en pesquerías de arrastre a nivel mundial. Aquí se exponen los resultados de los primeros ensayos usando rejillas separadoras tipo Nordmøre con cuatro espacios diferentes de separación entre barras para la flota de arrastre del Golfo de Cádiz que captura crustáceos como recurso principal. Se realizaron un total de 288 lances válidos y se capturaron unas 67 especies comerciales diferentes. El porcentaje de escape y la selectividad del escape por tallas fueron calculados para las especies comerciales y by-catch más importantes. Los resultados muestran un decrecimiento en el porcentaje de biomasa escapada al aumentar la separación entre barras para dos de las especies objetivos; gamba blanca (Parapenaeus longirostris) y cigala (Nephrops norvegicus), con porcentajes que oscilan desde 24 a 8% para la primera y 86 a 9% para la segunda, con las rejillas de 15 mm y 30 mm de separación entre barras respectivamente. En general, se obtienen altos porcentajes de escape para la mayoría de especies de peces y cefalópodos. Los resultados para merluza (Merluccius merluccius), como principal especie by-catch, muestran un decrecimiento en el porcentaje de escape desde 96% a 71% con el aumento de la separación entre barras respectivamente. Nuestros resultados sugieren que la rejilla de 30 mm de separación entre barras podría ser la más efectiva para la flota que dirige su captura a crustáceos en aguas profundas del Golfo de Cádiz pero diferentes medidas de mitigación serían necesarias para el resto de métiers de la pesquería de arrastre multiespecífica de esta zona....
A Sort‐X grid device with four different bar‐spacing grids (25, 30, 40 and 50 mm) was tested in the Gulf of Cádiz (GoC) on‐board commercial trawlers. A total of 83 fish, five crustacean and nine cephalopods species were sampled in 282 hauls. Most of the target and commercial bycatch species were sorted out by the grid with the exception of hake. Merluccius merluccius (L.). Additionally, common pandora, Pagellus erythrinus (L.), sardine, Sardina pilchardus (Walbaum), octopus, Octopus vulgaris Lamark, and cuttlefish, Sepia officinalis L., also showed a sizeable retention for some of the grid bar spacing. Statistical modelling of selectivity at length for hake found influence of depth on the selection parameters. Lengths at 50% retention for hake were estimated to be 27.4, 30.3, 36.3 and 42.3 cm TL for 25–50 mm bar spacing, respectively, all above the minimum conservation reference size (MCRS) in the GoC. The probability of hake contacting the grid was estimated as 0.95. Overall, although the selective device showed a good performance for hake, it is not appropriate for improving the fishing pattern of a multi‐species trawl fishery such as that of the GoC.
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