Depredation in the Portuguese pelagic longline fleet in the Indian Ocean

Depredation has aroused great interest over the last few decades due to the expansion of distant fishing, in particular pelagic and bottom longlines. As part of the monitoring of the Portuguese pelagic longline fleet, catches and depredation records were taken by scientific observers on board commercial vessels from Portugal. Data were compiled and analyzed for the periods 2011-2015 in the southern area of the Indian Ocean. A total of 445 fishing sets were monitored in the period, with a total of 26,366 fish catches, including 778 depredation events. The percentage of depredation increasing yearly along the time series. The two main predated species were swordfish and escolar, with significant differences in prey size for swordfish, but not for escolar. However, the highest proportions of depredation were observed on tuna and small pelagic fishes. For swordfish specimens, the effects of spatial variables (latitude and longitude) were significant on the rate of depredation events. The results presented in this study provide a first overview of the depredation patterns in the Portuguese pelagic longline fishery in the Indian Ocean that can help to promote more informed management and conservation measures.