Historical baleen plates indicate that once abundant Antarctic blue and fin whales demonstrated distinct migratory and foraging strategies

Southern hemisphere blue (Balaenoptera musculus intermedia) and fin
(Balaenoptera physalus) whales are the largest predators in the Southern
Ocean, with similarities in morphology and distribution. Yet,
understanding of their life history and foraging is limited due to current
low abundances and limited ecological data. To address these gaps,
historic Antarctic blue (n = 5) and fin (n = 5) whale baleen plates,
collected in 1947–1948 and recently rediscovered in the Smithsonian
National Museum of Natural History, were analyzed for bulk (δ13C and δ15N)
stable isotopes. Regular oscillations in isotopic ratios, interpreted as
annual cycles, revealed that baleen plates contain approximately six years
(14.35 ± 1.20 cm yr–1) of life history data in blue whales and four years
(16.52 ± 1.86 cm yr–1) in fin whales. Isotopic results suggest that: 1) in
the 1940s, blue and fin whales fed at the same trophic level but in
slightly different habitats, 2) fin whales appear to have had more regular
annual migrations, and 3) fin whales may have migrated to ecologically
distinct sub-Antarctic waters annually while some blue whales may have
resided year-round in the Southern Ocean. These results reveal differences
in ecological niche and life history strategies between Antarctic blue and
fin whales during a period when their populations were more abundant than
today, and before major human-driven climatic changes occurred in the
Southern Ocean.