Can Circle Hook Offset Combined with Baiting Technique Affect Catch and Bycatch in Pelagic Longline Fisheries?

Circle hooks have become a standard requirement in many commercial longline fisheries in the united states, and are used increasingly worldwide. Circle hooks, when compared to J-hooks, are thought to reduce bycatch without significantly decreasing (and possibly increasing) catch of most target species. Circle hook offset and baiting technique are also thought to influence bycatch and mortality of species of concern, such as sea turtles and billfishes. We compared non-offset circle hooks to those with a 10° offset and single or threaded baiting techniques in the united states atlantic and gulf of mexico pelagic longline fishery. Offset and/or baiting techniques were compared within sets targeting one of three species independently: swordfish, Xiphias gladius linnaeus, 1758, yellowfin tuna, Thunnus albacares (bonnaterre, 1788), and bigeye tuna, Thunnus obesus (lowe, 1839). Most comparisons of catch and bycatch did not differ between gears or techniques. In swordfish-directed sets, we found a 46% decline in catch of atlantic sailfish when using 18/0 non-offset circle hooks single baited with mackerel compared to 18/0 10° offset circle hooks with threaded mackerel. In yellowfin tuna sets, single baiting significantly decreased target catch by 22% and escolar catch by 28%, compared to threaded baiting. We detected no significant effect of any of the offset or baiting treatments on the bycatch of sea turtles and most other species of concern due to the rarity of capture events. We conclude, in part, that bycatch mitigation research in other fisheries with larger detrimental population level impacts to species of concern may potentially yield greater conservation benefits.