Dine and Dash: Changing Harbor Seal Numbers and Habitat Use at the Developing Bellingham Waterfront

• Main Author: Conwell, Holland
• Format: Text
• Language: English
• Published: Western CEDAR 2023
• Subjects: marine mammals; harbor seals; salmon; predation; wildlife management; Pacific Northwest; Biology; Pacific; harbor seal; Phoca vitulina
• Online Access: https://cedar.wwu.edu/wwu_honors/735; https://cedar.wwu.edu/context/wwu_honors/article/1721/viewcontent/Conwell_capstone_reflection.PDF

The lack of recovery of some Pacific salmon stocks (Oncorhynchus spp.) in the Pacific Northwest has been blamed in part on predation by pinnipeds, particularly the harbor seal (Phoca vitulina). A proposed non-lethal method aimed at managing seal predation on salmon is the removal of artificial haul-out sites. However, the effectiveness of this non-lethal management method has not been examined. To address this knowledge gap, I analyzed harbor seal numbers and habitat use at the developing downtown Waterfront in Bellingham, WA, USA. I examined harbor seal numbers from 2007-2023 throughout multiple log boom removal events at two known harbor seal haul-out sites adjacent to a salmon foraging site. Western students conducted visual surveys of harbor seals during daylight hours and used binoculars to count the number of harbor seals hauled-out and in the water. Harbor seal count data was analyzed using Generalized Additive Models (GAMs) to model seasonal (month) and long-term (year) trends in hauled-out and swimming seal numbers. I found a decreasing trend in the number of hauled-out seals at both haul-out sites by year from 2007-2023 and 2017-2023 amidst log boom removal (p<2e-16 and p=0.00158 respectively). Conversely, I found an increase in the number of seals swimming at the adjacent salmon foraging site by year from 2011-2023 throughout the removal of log booms (p<2e-16). A November peak in seal activity coinciding with the fall salmon return at the salmon foraging site was additionally reflected in the number of swimming seals at both haul-out sites by month. Therefore, despite the long-term decrease in the number of hauled-out seals, artificial haul-out removal did not appear to be effective at driving seals away from salmon habitat at the downtown Bellingham Waterfront. (Because this paper is to be submitted for publication elsewhere, the personal reflection here will serve as a placeholder until the paper is available to be linked.)