Catching efficiency and selectivity of gillnets and trammel nets in coral reefs from southwestern Puerto Rico

Abstract

A comparative fishing experiment was conducted to investigate the capture efficiency and selectivity of bottom-set gillnets and trammel nets. Twelve gillnets and trammel nets of different mesh sizes (7.6, 8.8, 10.1, and 12.6 cm stretched mesh) and hanging ratios (1:1, 1:2, and 1:3) were fished from May 1990 to September 1991 in coral reef (inner and outer reef) and mangrove areas off La Parguera, Puerto Rico. Significant differences in capture due to mesh size and hanging ratio for the inner and outer reef were observed. However, catches in mangroves were only influenced by hanging ratio. Significant interaction between mesh size and hanging ratio influencing the catches of both gears was found. The interaction behaved in an oppositive manner between the two gears. Largest catches in gillnets were obtained by combination of high hanging ratio (1:3) with large meshes (12.7 cm) or low hanging ratio (1:1) with small meshes (7.6). For trammel nets, the largest catches were obtained with low hanging ratio (1:1) with large meshes (12.7 cm) or high hanging ratio (1:3) with small meshes. This oppositive interaction may arise from the different mode of capture of these gears. Selectivity curves were generated for four species: white grunt ( Haemulon plumieri), bluestriped grunt ( Haemulon sciurus), stoplight parrotfish ( Sparisoma viride) and sea bream ( Archosargus rhomboidales). The selectivity curves of gillnets and trammel nets were unimodal. Optimum length increases as the mesh size increases, and the selection range becomes wider as hanging ratio increases.