Assessing the current status of Hexanchus griseus in the Mediterranean Sea using local ecological knowledge

Abstract

Fishermen from 9 countries distributed throughout the Mediterranean Sea were interviewed between May and December 2019 with the aim of compiling information about the current impact of fisheries on a large deepwatershark species, the bluntnose sixgill shark (Hexanchus griseus). A total of 382 professional fishermenbelonging to 6 different gears (bottom trawling, bottom longline, drifting longline, trammel nets, gillnets andpolyvalent) took part in the study. Bottom trawlers were the most interviewed fishermen (n = 148) and the bestfleet coverage was obtained for bottom longline (38.89%). Results showed most captures of H. griseus occur in theWestern and Central Mediterranean Sea, particularly during the warm months of the year and most commonly bybottom trawlers and bottom longliners. At-vessel mortality (AVM) was rather low in all gears but a slightlyhigher degree of individual mortality is suggested in trammel and gillnets. The population trend of H. griseus inthe Mediterranean Sea could not be inferred from the interviews as answers were highly variable, but the overalltrend in some countries may suggest this species is showing signs of population decrease. The results of this studyare mostly aligned with the latest IUCN assessment but also recommend reviewing the current status of H. griseusin the Mediterranean basin. Further empirical research on post-release mortality would also be advisable toimplement measures that help reduce this source of mortality.