Effects of Hook and Bait on Sea Turtle Catches in an Equatorial Atlantic Pelagic Longline Fishery

Abstract

Here we report a component of the results of the sElEct-pal project, namely marine turtle bycatch composition and rates, hooking location, and status at haulback and at release for several hook-bait combinations in a portuguese commercial longline fishery targeting swordfish in the atlantic equatorial region. In total, 221 longline sets were deployed during the fishing season (february-october) by the portuguese fleet operating in the area. Three different hook types were tested, traditional J-hook (9/0) and two 17/0 circle hooks (non-offset and 10° offset), but only one bait type was used in each set (Scomber spp. or Illex spp.). Four species of sea turtle were caught, most consisting of the olive ridley, Lepidochelys olivacea (Eschscholtz, 1829), and leatherback, Dermochelys coriacea (Vandelli, 1761). The highest mean bycatch per unit effort (bpuE) values for both species combined and for the individual species occurred with the J-hook. The 10° offset circle hook baited with mackerel provided a reduction of 88% and 85% on the bycatch rates, for all turtles combined and olive ridleys, respectively. Although hook location was species-specific and only bait appeared to be driving bycatch rate differences, most sea turtles were caught in the mouth, except for leatherbacks. Only hook type contributed significantly to haulback mortality, with J-hooks associated with slightly higher mortality rates.