Marine mammal population decline linked to obscured by-catch

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Meyer, Stefan, Robertson, Bruce C., Chilvers, B. Louise, Krkošek, Martin
• Format: Text
• Language: English
• Published: National Academy of Sciences 2017
• Subjects: Biological Sciences; New Zealand; Southern Ocean
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5676876/; http://www.ncbi.nlm.nih.gov/pubmed/29078271; https://doi.org/10.1073/pnas.1703165114

Declines of marine megafauna such as turtles, pinnipeds, and whales are often related to mortality caused by capture or entanglement in fisheries gear. To help recovery of these species, trawl fisheries have implemented exclusion devices that release nontarget species. Despite decades of use, there has been no empirical evaluation of whether or not exclusion devices aid recovery of affected species. Long-term data on the endangered New Zealand sea lion and a trawl fishery in the Southern Ocean indicate that exclusion devices have paradoxically contributed to ongoing decline rather than recovery. Exclusion devices obscure the postrelease impact of elevated mortality or reproductive failure; meanwhile, reduced levels of reported by-catch may mislead management that continued decline is not associated with fisheries.