Selectivity assessment of gillnets in the artisanal fishery of the Sinu River estuarine delta zone, Colombian Caribbean

Abstract

One of the most important artisanal fisheries in northern Colombia is being developed in the deltaic estuarine zone of the Sinú River (ZDERS). Little is known about the impact on the resource caused by fishing gears and even less about those which are not allowed. In order to estimate the selectivity of gillnets or «trasmallos» in this artisanal fishery, selection parameters for five of the main commercial species, Mugil incilis, Eugerres plumieri, Prochilodus magdalenae, Ariopsis bonillai and Centropomus undecimalis, in 2001 and 2002, length frequency data for mesh sizes in the main landing sites were collected. A total of 16427 individuals were caught with mesh sizes from 5.08 to 10.16 cm stretched. It has been determined that gill nets exerts a negative pressure on the studied species when used with mesh sizes of 5.08 and 7.62 cm. Optimal catch length for each species, estimated with different mesh sizes, were found below the mean length of sexual maturity. The same effect was observed with those species reaching big sizes (C. undecimalis, A. bonillai and P. magdalenae) when fished with gill nets whose mesh size was 10.16 cm. Observed Selection factor values were low for E. plumieri and P. magdalenae, and high for M. incilis, A. bonillai and C. undecimalis. Differences in selection factor were attributed to the morphology of each species, tall (E. plumieri and P. magdalenae), oblong (M. incilis and A. bonillai) and long fishes (C. undecimalis). Minimum catch length and mesh sizes for each species are recommended. Some aspects on the sustainable management of the fish resource in the ZDERS fishery are discussed.