Fish fauna associated with floating objects sampled by experimental and commercial purse nets

Based on the commercial surrounding nets traditionally used in the Coryphae na hippurus fishery, we designed an experimental purse seine (64 m long and 14 m high, with a purse line and a central codend of 2 mm mesh) for sampli ng fish fauna associated with flotsam. Taxa, number, biomass and sizes of f ishes caught with both types of gear around fish aggregation devices were c ompared. From 63 hauls with the experimental net, we caught 11370 fishes be longing to 17 families and 26 species. In contrast, 816 fishes belonging to 7 species and 5 families were collected from 39 commercial hauls. Despite differences in number of hauls for each net, the curves of cumulative speci es richness showed that additional hauls could not increase the number of s pecies collected with the commercial net. The most abundant species from ex perimental net catches were Trachurus picturatus, which represented over 80 % of the specimens caught in spring and summer, Naucrates ductor, which rep resented about 50% of autumn catches, both in terms of abundance and biomas s, and Seriola dumerili, which represented 46% and 21% of the samples taken in summer and autumn respectively. Seriola dumeril was also frequent in co mmercial net catches, in which T. picturatus did not appear, while Coryphae na hippurus and N. ductor represented more than 85% of both abundance and b iomass. Large differences between the two types of net were also obtained i n the mean fish weight and length frequency distributions of the catches by season. Fish caught with the experimental net ranged from 6 to 570 mm leng th, while fish collected from commercial hauls had a size range of 35 to 70 0 mm. The effectiveness of the experimental net in catching small fishes sh owed that it can be an optimal sampling method not only in the study of fis h fauna associated with flotsam, but also in studies to catch early life st ages.