Toothed whale and shark depredation and bycatch in the longline fishery of French Polynesia
Résumé
Marine megafauna feeding on fishery catches (depredation) or being incidentally caught on fishing gear
(bycatch) have become important issues. Their socioeconomic and conservation stakes have been increasingly
studied across the world fisheries. They remain understudied in the Pacific Ocean, where longline tuna fisheries
reported such interactions. In this study, we provide the first assessment of bycatch and depredation by sharks
and odontocetes on longlines in French Polynesia between 2000 and 2018, using data from observers reporting,
captains’ logbooks, questionnaires and additional monitoring by authors during three fishing trip. We found that
less than 2% of the catch had been depredated, and that shark depredation was more common than odontocete
depredation. Shark bycatch was important (20,000 sharks annually, 0.5 shark every 1000 hooks) and odontocete
bycatch seemed low (13 occurrences in 18 years), though we identified clear reporting flaws. We discuss the
range of uncertainty associated with our assessment, based on the current reporting systems, and the potential
consequences of depredation and bycatch on tuna fisheries, as well as on shark and odontocete populations in
French Polynesia.