PhD Thesis Defense: Fanny Couture

PhD Defense by

Fanny Couture

Date: Wednesday April 3, 2024
Time: 4:00 pm
Location: Room 200, Graduate Student Centre (6371 Crescent Road).

Assessing the Influence of Climate Variability and Resource on Prey Availability for Southern Resident Killer Whales

The fish-eating southern resident killer whale population (SRKW, Orcinus orca) inhabits the coastal waters of the northeast Pacific and was listed as Endangered in both Canada and the United States in the early 2000s. With only 75 individuals remaining, immediate research is needed to ascertain the primary factors limiting this population. As it has emerged that food availability could be an important factor limiting the growth of this whale population, a bioenergetic model was built to assess their ability to meet energy needs from 1979 to 2020. This was a period of substantial changes in prey availability for SRKW, and results indicated a potential energy deficit in six of the last 40 years. Further, recent evidence suggested that limitations in their primary food source, Chinook salmon (Oncorhynchus tshawytscha), could result from multiple factors. An ecosystem model was constructed to examine how marine mammal predation, fishing activities, and large-scale climatic patterns could influence Pacific salmon productivity. The results of the model revealed that all salmon groups have experienced increasing predation pressure from marine mammals since 1979 while variations in population abundance have also been driven by bottom-up effects linked to anomalies in primary productivity. This dissertation also sought to investigate future management strategies for enhancing prey availability for SRKW. The model was projected forward over a 150-year timespan under different fishing and predation scenarios, and results indicated that a reduction in pinniped populations could facilitate the recovery of most Chinook salmon stocks in the northeast Pacific, thereby supporting the growth of the SRKW population. Finally, it seemed important to determine if integrating spatio-temporal data for highly mobile marine mammals and salmon could still allow for accurate predictions of their population trends in the model. The spatial-dynamic model successfully mirrored the population dynamics projected by the temporal model and provided a unique comparison of both modules. Overall, this research underscores the need for practical management measures to protect Pacific salmon and the SRKW population. It provides valuable insights into the concurrent impacts of bottom-up and top-down processes on these populations over recent decades.

Committee
Dr. Villy Christensen (supervisor)
Dr. Carl. Walters
Dr. David Rosen
Dr. Brian Hunt
Dr. Charles Menzies