Earlier migration and distribution changes of albacore in the Northeast Atlantic

Marine species have exhibited trends in their geographic distribution and phenology in recent decades, and these changes are triggered by climate variability or anthropogenic pressures. Northeast Atlantic albacore has recently been identified to show changes of this nature, although the underlying causes are still uncertain. The aim of this work was to analyse the Northeast Atlantic albacore distribution shifts and phenological changes during the trophic migration that juveniles undertake from late spring to autumn and to identify potential causes of such variability. Specifically, time series of albacore catches of the Basque trolling fleet were studied and compared with trends derived from a null ecological niche model using very large number of catch observations (27,982). The results showed an earlier albacore migration of 2.3 days per decade during the period of 1981-2017, which was partly associated with the recent warming of the sea. The trend analysis of the catch distribution also detected a significant north-westward trend in catch observations and a northward trend in species habitat. In contrast, both latitudinal trends were uncorrelated. This result suggests that interannual species distribution shifts are mainly related to factors other than oceanic-climatic variability, such as fleet behaviour or prey changes.