A risk assessment for Pacific leatherback turtles (Dermochelys coriacea)

Abstract

Leatherback turtles (Dermochelys coriacea) are critically endangered in the eastern and western Pacific Ocean. Here, I estimate the magnitude of two likely causes of their decline: (i) bycatch by longline fishing vessels and (ii) coastal sources of mortality. I calculate point estimates of longline bycatch based on turtle catch rates from the US Hawaii-based fleet and effort data for the international Pacific longline fleet. I estimate the intrinsic growth rate of the population and the magnitude of coastal mortality by fitting a simple logistic model. In the western and central Pacific, coastal sources lead to a 13% annual mortality rate, compared with a point estimate of 12% from longlining. In the eastern Pacific, coastal sources account for a 28% annual mortality rate, compared with a point estimate of only 5% from longlining. A Bayesian risk assessment reveals the importance of reducing coastal sources of mortality, as well as longline bycatch, if the populations are to avoid extinction. International efforts to protect the leatherback should expand beyond focusing solely on longline bycatch and should attempt to reduce coastal harvest of adult females and eggs, as well as reduce bycatch by inshore gears such as gillnets.