Humpback Whale Prey Consumption and the Effects of a Recovering Population on the Strait of Georgia Food Web
Date: December 12, 2024
Time: 9:00-11:30 am
Location: AERL 107
The rapid recovery of the North Pacific humpback whale (Megaptera novaeangliae) population, following intense depletion from commercial whaling, presents both conservation success and potential ecosystem effects. In the northern Strait of Georgia, British Columbia, where humpback whales have recently re-established, this study aimed to assess their diet composition, evaluate broader food web effects of their recovery, and estimate carrying capacity for the species in this area. Humpback whale skin samples (n=108) and key prey items—juvenile herring (n = 187), adult herring (n = 23), euphausiids (n = 69), and amphipods (n = 6)—were collected during the summers of 2022 and 2023 and analyzed for stable carbon (δ13C) and nitrogen (δ15N) isotopes. Bayesian mixing model (MixSIAR) analyses indicated that humpback whales in the Strait of Georgia primarily forage on euphausiids (85%, range: 76–94%) and juvenile herring (10%, range: 0.8–21%) in summer, with minimal contributions from adult herring and amphipods. To assess effects of humpback whale on the northern Strait of Georgia food web, an ecosystem model was developed in the modelling software Ecopath with Ecosim. The model incorporated updated humpback whale diet composition, abundance estimates, and consumption rates. The model predicted that a growing number of humpback whales would primarily affect euphausiids and juvenile herring, with minor effects on other species. Prey biomass declines became significant when humpback whale abundance in the northern Strait of Georgia exceeded approximately 180 individuals. The maximum year-round carrying capacity for the region was estimated at around 388 to 417 (range: 372–478) individuals, with euphausiids as the limiting factor. This research offers critical insights into humpback whale feeding ecology and cascading effects of their recovery. These findings contribute to management strategies for both humpback whales and their prey, supporting balanced conservation efforts for the region.
Examining committee:
Dr. Villy Christensen (Supervisor and Chair)
Dr. David Rosen (External Examiner)
Sheila Thornton, Fisheries and Oceans Canada (Committee Member)