Habitat use in Atlantic bluefin tuna Thunnus thynnus inferred from diving behavior

Abstract

To examine habitat use in Atlantic bluefin tuna Thunnus thynnus, we used time series records from 20 archival tags and 7 pop-up satellite archival tags. Daily vertical profiles were classified into 3 dive types: (1) profiles restricted to surface waters by either bathymetry or thermal constraints; (2) profiles with frequent V-shaped dives that may be associated with transiting or searching behaviors; and (3) U-shaped profiles associated with putative foraging behavior. Fixed kernel probability contours were calculated for each of the dive profile classes. Key potential North Atlantic foraging habitats were identified in the NW Atlantic (Gulf of Maine/Scotian Shelf, Grand Banks and Flemish Cap), off Florida and the Bahamas and in the NE Atlantic. These ‘hotspot’ regions encompass areas of high seas that may be important to future conservation and management of the species. U-shaped dive profiles were shallower and surface returns were more frequent in areas where subsurface temperatures were coldest. The presence of Atlantic bluefin tuna coincided with peak productivity and sea surface temperatures in 3 of the 5 hotspot areas. Further analyses examined spatial and temporal patterns of transatlantic migrations and deep diving behavior in the Strait of Gibraltar.