Summer Diet of Humpback Whales in the Northern Strait of Georgia, British Columbia (Canada), Revealed by Stable Isotope Analysis

Abstract

North Pacific humpback whales ( Megaptera novaeangliae ) have recovered rapidly following their depletion by commercial whaling. Diet studies are necessary to assess food web implications of their recovery. This study investigates the diet composition of humpback whales foraging in the northern Strait of Georgia, British Columbia, Canada, an area experiencing a recent return of humpback whales. Humpback whale skin samples ( n = 108), juvenile herring ( n = 202), adult herring ( n = 23), euphausiids ( n = 63), and amphipods ( n = 6) were collected in the summer months of 2022 and 2023 and analyzed for carbon (δ 13 C) and nitrogen (δ 15 N) stable isotopes. Applying these isotope data, the Bayesian mixing model MixSIAR was used to estimate the contribution of each prey type to humpback whale diet. We found that, during the summer months, humpback whales primarily consumed euphausiids (85.3%, range: 76.4%–94.0%) and juvenile herring (10.2%, range: 0.8%–21.0%), with minimal contributions from adult herring and amphipods. Diet composition was consistent across months and years. These findings provide critical insights into humpback whale foraging ecology, informing conservation efforts for both predator and prey species in the region.

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