The environment drives Atlantic bluefin tuna availability in the Gulf of Lions

Abstract

AbstractAtlantic bluefin tuna (ABFT) is a migratory species whose exploitation is affected by its migratory behaviour. ABFT can be found the whole year round in the Gulf of Lions (GoL), with the exception of the May/June/July spawning season. The date at which ABFT fishing resumes in the GoL after spawning is variable and affects both the summer longline fishery and the local aerial survey used to derive a fisheries‐independent index of abundance used in the stock assessment. We investigated whether environmental conditions could explain inter‐annual variability in ABFT availability in the GoL. We focused on Sea surface temperature (SST) and northern wind events looking at changes in the ABFT summer longline fishery start date and quota completion date. Years with weaker northern wind events displayed a higher SST and were associated with a delay in ABFT catch by up to more than one month, whereas the bulk of the catch was completed earlier. A scale‐dependent analysis of the densities of ABFT schools detected during the aerial survey show consistent associations between the short‐term fluctuations in northern wind and SST and the densities of ABFT schools detected. When considering the trends these effects appeared reversed, higher SST and weaker northern wind being associated with an increase in ABFT school density. The implication of these results on the aerial survey and for the exploitation and conservation of ABFT are discussed in the light of the literature on its migratory behaviour in the context of climate change.