The number of sea turtles killed as bycatch in US coastal waters has dropped by an estimated 90 percent since 1990, to 4,600, according to a new study by researchers at Duke University Project GloBAL and Conservation International, published in the scientific journal Biological Conservation.
Total sea turtle takes used to surpass 300,000 annually, of which 70,000 were killed. All six marine turtle species in US waters – including loggerheads, leatherbacks and green sea turtles – are categorised as threatened or endangered. Scientists used data collected from 1990-2007 by the National Marine Fisheries Service (NMFS) to find out bycatch rates across more than 20 fisheries operating in US coastal waters. They found that overall rates have fallen about 60 percent. Shrimp trawls made up 98 percent of them.
"Our findings show that there are effective tools available for policymakers and fishing industries to reduce sea turtle bycatch, as long as they are implemented properly and consistently," said Elena Finkbeiner, a PhD student at Duke and lead author of the paper.
The strategies that have helped reduce bycatch are using circle hooks and dehooking gear in longline fisheries to reduce the severity of turtle injuries; the use of turtle excluder devices (TEDs) in shrimp trawl nets to let sea turtles escape; and implementing time-area closures to restrict fishing activities when and where turtles are most likely to appear in the highest numbers.
Piecemeal regulation remains troublesome, the study notes. Sea turtles are managed on a fishery-by-fishery basis, with bycatch limits set for each fishery without considering the overall population impacts of all the takes together, which breeds total allowed takes exceeding what sea turtle populations can sustain.
"One of the problems is that we don't have that magic number that serves as a quota across all fisheries," said co-author Bryan Wallace, director of science for Conservation International's Marine Flagship Species Programme and adjunct faculty member at Duke's Nicholas School of the Environment.
Actual bycatch rates are likely even higher, the study notes, because in many fisheries and particularly the shrimp trawl the number of on-board observers documenting bycatch is relatively low.
FIS