The effects of circle hooks on bycatch and target catches in Australia's pelagic longline fishery

We assess the performance of circle hooks, which are promoted as a measure for improving the survival of marine turtles following interactions with pelagic longlines. We conducted experiments off eastern Australia on commercial fishing vessels that alternated circle hooks (mostly size 14/0) and Japanese tuna hooks along their longlines. Most animals were hooked in the lip or jaw, regardless of hook type. There was no difference in the mean size of animals caught on the two types of hook, except for striped marlin (Tetrapturus audax), which tended to be larger on tuna hooks. Most species had an equal or lower probability of being alive on circle hooks than tuna hooks. Catch rates on circle hooks exceeded those on tuna hooks for most species. These included several target species, such as albacore tuna (Thunnus alalunga), yellowfin tuna (Thunnus albacares) and striped marlin, and bycatch, including several shark species. The differences in catch rates were large enough to increase total catches and financial returns. The financial benefits of increased catches outweighed the costs of converting to circle hooks. The results indicate that the adoption of small circle hooks by longliners will not be detrimental to financial returns.