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 deep-water shark species, the bluntnose sixgill shark (Hexanchus griseus). A total of 382 professional fishermen belonging to 6 different gears (bottom trawling, bottom longline, drifting longline, trammel nets, gillnets and polyvalent) took part in the study. Bottom trawlers were the most interviewed fishermen (n = 148) and the best fleet coverage was obtained for bottom longline (38.89%). Results showed most captures of H. griseus occur in the Western and Central Mediterranean Sea, particularly during the warm months of the year and most commonly by bottom trawlers and bottom longliners. At-vessel mortality (AVM) was rather low in all gears but a slightly higher degree of individual mortality is suggested in trammel and gillnets. The population trend of H. griseus in the Mediterranean Sea could not be inferred from the interviews as answers were highly variable, but the overall trend in some countries may suggest this species is showing signs of population decrease. The results of this study are mostly aligned with the latest IUCN assessment but also recommend reviewing the current status of H. griseus in the Mediterranean basin. Further empirical research on post-release mortality would also be advisable to implement measures that help reduce this source of mortality.