Quantifying the roles of competing static gears: comparative selectivity of longlines and monofilament gill nets in a multi-species fishery of the Algarve (southern Portugal)

Karim Erzini, Jorge M.S. Gonçalves, Luís Bentes, Pedro G. Lino, Joaquim Ribeiro, Konstantinos I. Stergiou
2003 Scientia Marina  
Fishing trials with monofilament gill nets and longlines using small hooks were carried out in Algarve waters (southern Portugal) over a one-year period. Four hook sizes of "Mustad" brand, round bent, flatted sea hooks (Quality 2316 DT, numbers 15, 13, 12 and 11) and four mesh sizes of 25, 30, 35 and 40 mm (bar length) monofilament gill nets were used. Commercially valuable sea breams dominated the longline catches while small pelagics were relatively more important in the gill nets.
more » ... ll nets. Significant differences in the catch size frequency distributions of the two gears were found for all the most important species caught by both gears (Boops boops, Diplodus bellottii, Diplodus vulgaris, Pagellus acarne, Pagellus erythrinus, Spondyliosoma cantharus, Scomber japonicus and Scorpaena notata), with longlines catching larger fish and a wider size range than nets. Whereas longline catch size frequency distributions for most species for the different hook sizes were generally highly overlapped, suggesting little or no differences in size selectivity, gill net catch size frequency distributions clearly showed size selection. A variety of models were fitted to the gill net and hook data using the SELECT method, while the parameters of the logistic model were estimated by maximum likelihood for the longline data. The binormal model gave the best fits for most of the species caught with gill nets, while the logistic model adequately described hook selectivity. The results of this study show that the two static gears compete for many of the same species and have different impacts in terms of catch composition and size selectivity. This information will be useful for the improved management of these small-scale fisheries in which many different gears compete for scarce resources. Portugal) durante un año se han llevado a cabo pescas experimentales con redes de enmalle monofilamento y palangres con anzuelos pequeños. Se utilizaron cuatro tamaños (Calidad 2316DT, números 15, 13, 12 y 11) de anzuelos curvados y aplanados, de la marca: "Mustad", y redes de enmalle monofilamento de cuatro tamaños de luz de malla 25, 30, 35 y 40 mm. Por su valor comercial, los espáridos son las especies más importantes de las capturadas por los palangres mientras que los pequeños pelágicos son los de mayor importancia relativa de las capturadas por las redes de enmalle. Se han encontrado diferencias significativas entre los dos tipos de artes en las distribuciones de frecuencias de tallas para todas las especies más importantes capturadas por ambas artes (Boops boops, Diplodus bellottii, Diplodus vulgaris, Pagellus acarne, Pagellus erythrinus, Spondyliosoma cantharus, Scomber japonicus y Scorpaena notata). Con los palangres se capturaron ejemplares de mayor tamaño y en un rango más amplio que con las redes. Mientras que las distribuciones de frecuencias de tallas de las capturas de los diferentes tamaños de anzuelos se solapan en la mayoría de las especies, sugiriendo que no hay diferencias en la selectividad por tamaño o son muy pequeñas, las distribuciones de frecuencias de tallas de las redes de enmalle muestran claramente selección por tamaño. Los datos obtenidos, tanto con las redes de enmalle como con los anzuelos, se *
doi:10.3989/scimar.2003.67n3341 fatcat:tzppuhoptfenne6gjtoy5k3xsa