Results from the First WCPFC Workshop on Joint Analysis of Sea Turtle Mitigation Effectiveness

Clarke S, Peatman T, Caillot S (2016) Results from the First WCPFC Workshop on Joint Analysis of Sea Turtle Mitigation Effectiveness. WCPFC, Bali, Indonesia

The first of two joint-analysis workshop on the effectiveness of sea turtle mitigation in longline fisheries was held in Honolulu in February 2016. This ABNJ (Common Oceans) Tuna project sponsored workshop was attended by 31 participants from 14 countries from all three oceans, as well as invited IGOs and NGOs. The first workshop characterised current sea turtle interaction and mortality rates under existing fishing operations using observer data from a variety of sources representing over 2,300 turtles caught by 31 fleets between 1989 and 2015. There were three types of analyses undertaken for leatherback, loggerhead, green and olive ridley turtles: 1) estimating the effects of various operational variables on interaction rates at the set level; 2) estimating how turtle interaction rates vary by hook position within baskets; and 3) estimating the effects of various operational variables on turtle at-vessel mortality rates. Post-release mortality rates were not considered due to a lack of available information. In the first analysis hook category (shape and size), bait species, hooks per basket, and soak time had the largest effect on set level interaction rates, with significant decreases in interaction rates with the use of large circle hooks and/or finfish bait. In the second analysis interaction rates of olive ridley, loggerhead and green turtles with deep set longlines were highest for those hooks closest to floats. In the third analysis, at-vessel mortality rates were influenced by turtle species, with the lowest mortality rates for leatherback and loggerhead turtles, and increased mortality rates with increased fishing depths. Participants concluded that mitigation measures based on hook shape and size, bait species, and removal of the hooks nearest each float in deep longline sets should be priorities for further analysis. The workshop also generated preliminary species-specific maps of relative abundances. A Delphi technique peer review process is being considered to confirm these maps. A second workshop, to be held in November 2016, will focus on estimating baseline interaction and mortality rates under current fishing operations and testing various mitigation scenarios to determine their effectiveness in reducing impacts.