A Comparison of Circle and J Hook Performance Within the Grenadian Pelagic Longline Fishery

Abstract

The use of circle hooks in pelagic longline fisheries has often been proposed as a minimally disruptive means to minimize bycatch mortality. However, most studies have been in large scale fisheries, not the small-vessel fleets seen in many Caribbean countries. Size 16/0 circle hooks and 9/0 J hooks were alternated over 26 sets to assess the performance of circle hooks in the Grenadian pelagic longline fishery. Catch, mortality, hook location, length, and grade of fish were compared between hook types. No species-specific differences in at-vessel mortality rate or yellowfin tuna grade were found between hook types. However, significantly fewer billfish collectively (t = 2.36, p = 0.028), and sailfish specifically (t = 3.04, p = 0.005), were caught on circle hooks. Additionally, tunas caught with circle hooks had a 69% greater chance of external hooking compared to J hooks (χ2 = 4.38, p = 0.036). All other species analyzed had similar catch rates regardless of hook type (p < 0.05), including yellowfin tuna. The results of this study suggest that the Grenadian pelagic longline fishery – and other Caribbean fleets, by extension – could reduce impacts on billfish stocks by using 16/0 circle hooks without incurring negative effects on yellowfin tuna catch rate or grade. With many bycatch species populations at depressed levels, these results also provide further evidence that circle hooks should be the recommended terminal gear type when using a bycatch mitigation approach to manage pelagic longline fisheries while maintaining target catches for local and export markets.