Sharon Kay

Topic

Sharing the catch; Social and environmental correlates of body condition in threatened Northern Resident killer whales

Department of Geography

Date & location

• Thursday, September 12, 2024

• 1:00 P.M.

• David Turpin Building

• Room B215

Reviewers

Supervisory Committee

• Dr. Chris Darimont, Department of Geography, University of Victoria (Supervisor)

• Dr. Lance Barett-Lennard, Department of Zoology, UBC (Non-unit Member)

• Dr. Amy Rowley, Cetacean Conservation Research Program, Raincoast Conservation Foundation (Non-unit Member) 

External Examiner

• Dr. David Rosen, Institute for the Oceans and Fisheries, University of British Columbia 

Chair of Oral Examination

• Dr. Colin Bradley, Department of Mechanical Engineering, UVic 

Abstract

Effective conservation and management should consider a species’ social dynamics, given that resource scarcity can lead to intragroup conflict. When food is limited, the reallocation of shared resources may incur costs for group members who depend on provisioning or for members that provide shared food. Resident Killer Whales share prey within their stable kin-based groups (matrilines), but little is known about how social group composition might influence allocation of shared prey and associated individual physiological condition. Using drones, we collected aerial images to estimate body condition of Northern Resident Killer Whales over ten years (2014-2023) to evaluate the health of individuals, some across multiple years (n = 175 individuals from 39 matrilines), in a population of approximately 345 whales. Our first objective was to examine the association between individual body condition and the composition of their matrilines, while accounting for salmon availability. Our second objective was to evaluate if mothers with more offspring had lower body condition, and if this relationship depended on their offspring sex. Using two candidate model sets of generalized mixed effect models, we found that social variables influenced body condition. Specifically, males showed declines in body condition as the proportion of juveniles in the matriline increased, while females either showed no change or increased in condition. These sex-specific patterns suggest that males may receive reduced investment through prey sharing in families with more dependent young. Additionally, we found a negative relationship between the body condition of adult females and the number of offspring they have, indicating that adult females may also incur costs in provisioning offspring. Interestingly, these patterns did not depend on salmon abundance. Our results demonstrate how sociality can influence individual health and provides insights into intragroup conflict and parental investment in a species with lifelong parental care and high social stability.