Individual Variability in Foraging Success of Harbor Seals (Phoca vitulina) Preying on Pacific Salmon (Oncorhynchus spp.) Informs Predator Management

• Main Author: Freeman, Grace
• Format: Text
• Language: English
• Published: Western CEDAR 2021
• Subjects: predator; prey; trophic; management; culling; rogue individual; harbor seal; Pacific salmon; Phoca vitulina; Oncorhynchus spp; Biology; Pacific
• Online Access: https://cedar.wwu.edu/wwuet/1042; https://cedar.wwu.edu/context/wwuet/article/2069/viewcontent/Freeman_Thesis_Complete.pdf

The complexities of trophic dynamics complicate the management of predator populations. In some cases, targeted culling campaigns are meant to control predator populations. In these campaigns, predators are considered ‘rogue individuals’ based on visitation rates to a site. This definition carries the underlying assumption that all predators impact prey equally, however, individual variability in foraging success may compromise such an assumption. Thus, to test the hypothesis that foraging success varies among individual predators, I studied harbor seals preying on adult Pacific Salmon during the 2014-2019 fall salmon runs. I analyzed individual harbor seal visitation rate and foraging success based on photographs and field observations, and I employed Generalized Linear Mixed-Effects Models to determine individual variability in metrics of foraging success. Individual harbor seal identity better explained both total foraging success and the odds of success of a given foraging event when compared to models based on visitation rate alone. My data suggest that considering intraspecific variability and classifying ‘rogue individuals’ based on foraging success is a more accurate protocol for managing predator populations than relying solely on visitation rate of the predators.