Satellite tracking and stable isotope analysis link wintering and feeding grounds of North Atlantic baleen whales

Knowledge of the distribution of baleen whales throughout their annual cycle is critical for understanding their ecology, life history and behavior, and for their effective conservation. We combined analysis of stable isotopes (δ15N and δ13C) and satellite tracking data of blue (Balaenoptera musculus), fin (B. physalus) and sei whales (B. borealis) encountered in the Azores to determine their wintering ranges, foraging behaviour, and movements towards feeding grounds. Blue, fin and sei whales occupied distinct isotopic spaces and distance between species was mainly driven by differences in δ 13C, suggesting use of different wintering habitats. Fin whales had the lowest δ13C values, consistent with prey sources from offshore areas, whereas the δ13C-enriched signal of sei whales indicate foraging in coastal NW African waters. Blue whales’ δ13C values were intermediate between those of fin and sei whales. Fin whales showed the broadest range and highest δ15N values, suggesting a more diverse prey base with a greater contribution of higher-trophic level organisms. Sex had no effect on isotopic signal in any of the species, indicating similar trophic levels and dietary sources for males and females. Satellite-derived movements of blue (n=10) and fin whales (n=16) indicated foraging at middle latitudes and a mid-Atlantic corridor between the Azores and Iceland-Greenland. Tracks of 8 sei whales provided no evidence of foraging until whales reached the Labrador Sea. One sei whale tagged in September moved towards Canary Islands, where the tag stopped transmitting. Our work suggests a wintering range in temperate-tropical pelagic waters for fin and blue whales migrating through the Azores to Iceland-Greenland. It also shows that part of the sei whale population feeding in the Labrador Sea winter, and possibly breed, in the eastern Atlantic. We discuss these findings in light of current knowledge on the migration strategy and population structure of each whale specie