Historical niche partitioning of baleen whales in the western South Atlantic

Baleen whales are key marine predators that were heavily exploited throughout the 20th century, resulting in reductions in population size for many species. Whilst population recovery is evident for some species, baseline information on ecological niches is still unknown, rendering it difficult to forecast the manner in which baleen whales will reoccupy their former ecological niches as they recover. Biogeochemical analyses of bone fragments from 20th century whaling provide invaluable information on the foraging ecology and trophic niches of whale populations in the past, and provide a baseline for assessing recovery. Here, we combined Zooarchaeology by Mass Spectrometry (ZooMS) and DNA barcoding to assign bone specimens to species from 3 former whaling sites in the western South Atlantic, and used stable isotope analysis of carbon and nitrogen to infer differences in the long-term foraging preferences of baleen whales utilising western South Atlantic feeding grounds. These data sets indicate that baleen whale species partitioned prey resources with slight overlap in isotopic niches for 3 of the 4 species, with sei whales Balaenoptera borealis likely to be foraging predominantly on different feeding grounds relative to Antarctic blue B. musculus , fin B. physalus , and humpback Megaptera novaeangliae whales. Niche sizes reveal that Antarctic blue and sei whales are specialist feeders at the population level, suggesting that they are less likely to adapt to continuing climate change relative to more generalist fin and humpback whales. Characterising historical foraging baselines such as these are essential for assessing the ecological implications of changing oceans for recovering whale populations.