Hooking Mortality Of Oceanic Whitetip Sharks Caught In A Pelagic Longline Targeting Swordfish In The SW Indian Ocean: Comments On The Efficiency Of No-Retention Measures.
The Portuguese pelagic longline fishery in the Indian Ocean started in the late 1990’s, targeting mainly swordfish in the southwest region, but in the more recent period has also expanded to the southeast. Pelagic sharks are an important component of this fishery, with some species, such as oceanic whitetip, discarded due to management recommendations. This working document revises data on the hooking (at-haulback) mortality of oceanic whitetip sharks captured and discarded by this fishery. The overall at-haulback mortality for oceanic whitetip sharks was 50.0%, which is higher than the estimates for the Atlantic (34.2%). The specimen size is significant for the odds of at-haulback mortality, with mortality decreasing as specimen size increases. Caveats of this study are the limited sample size, the fact that it focuses only in one fishery and fleet, with data restricted mainly to the temperate southwest Indian Ocean. Additionally, this study focuses only on the short term immediately mortality, while the overall mortality might be higher due to the potential post-release mortality, that is still currently unknown. In conclusion, and even though preliminary, this work presents new and important information on the potential efficiently of the no-retention measures currently in place for oceanic whitetip sharks in the Indian Ocean.