Chance and necessity food web models inform trophic interactions of baleen whales in Southern New England

Baleen whales play important roles in marine ecosystems, but their trophic ecology is not well understood in many regions. Describing trophic interactions is challenging for baleen whales as necessary information on their diets and metabolic rates are limited, particularly for region-specific analyses. Here we use chance and necessity (CaN) modeling, which inherently accounts for uncertainty and incorporates randomness, to assess food web interactions in Southern New England, with a focus on the trophic ecology of humpback and fin whales. In our analysis, menhaden made up the largest proportion of the diet of humpbacks, while krill was the most substantial prey item for fin whales. Model results indicated that there was overlap in the diet compositions of these two species, but humpbacks fed primarily on finfish and fin whales fed primarily on invertebrates. We found strong bottom-up drivers throughout the food web, with evident bottom-up effects on population growth rates across all functional groups. Bottom-up effects were strongly evident for fin and humpback whales, and our results suggest that both species experience prey limitation. Prey species of fin and humpback whales were influenced by predation broadly but were not strongly controlled by predation from humpback or fin whales specifically. Our results provide context for studies assessing changes in baleen whale distribution and body condition and provide insight into drivers of population dynamics. This research demonstrates the utility of CaN modeling for estimating trophic flows and diet compositions, particularly for data-limited species in ecosystems with otherwise robust ecological time series.