Changes in billfish catch rates due to the use of different hooks and baits in the configuration of the surface longline gear targeting swordfish (Xiphias gladius) in the Atlantic Ocean

Abstract

Billfish catches obtained during a survey conducted on the commercial surface longline gear were analysed. Three hooks and two baits were tested in the intertropical areas of the Atlantic using 263 210 hook-bait observations. The catch rates and proportion of positive sets were analysed using a GLM (Delta-lognormal) at the species level. Zone was the most important factor (alone or in interaction with others) in explaining the catch rates and/or the proportion of positive sets of most billfish species caught. The factors tested (hook and bait) were not significant for any of the billfish species. Despite the lack of significance found for both factors, the results suggest that alternative hooks could produce changes in the mean CPUE of billfish of between –13% and +9% depending on the species and hook type used. The alternative bait (squid) might also produce changes in mean CPUE from around –7% to +18%. The interaction between the alternative hooks and bait could lead to changes in mean CPUE of between –24% to +45% depending on the combination of both factor and species considered. The model assumed was appropriate for both BUM and SPF but for other billfish species alternative error distributions could be explored. The selection of the area and the experimental design could play a decisive role when predicting the advantages or disadvantages of using certain elements in a fishing gear, particularly in the case of species with low prevalence in which the proportion of zero observations tends to be high.

http://www.co.ieo.es/tunidos/esp/..%5Cdocumentos%5Ciccat%5CCV065051778.pdf