Examining harbor seal predation impacts on Bellingham Technical College's salmon smolt release

• Main Authors: Gard, Madison, Acevedo-Gutierrez, Alejandro
• Format: Text
• Language: English
• Published: Western CEDAR 2023
• Subjects: smolt; salmon; pinniped; predation pressure; harbor seal; Phoca vitulina; Biology; Marine Biology; Pacific; Lontra; Pandion haliaetus
• Online Access: https://cedar.wwu.edu/wwu_honors/723; https://cedar.wwu.edu/context/wwu_honors/article/1709/viewcontent/auto_convert.pdf

Each year, federal, state, and tribal agencies dedicate time, money and resources to the rearing of hatchery-raised Pacific salmon (Oncorhynchus spp.) populations in the Salish Sea. Yet, many of these populations continue to decline, with several causes being proposed for preventing their recovery. Among the hypothesized causes, the presence of predators, particularly harbor seals (Phoca vitulina), and the timing of release of hatchery salmon, which may attract various types of predators, appear to be important for the survival of Chinook salmon (O. tshawytscha). At Whatcom Creek, in downtown Bellingham, WA, the Bellingham Technical College manages a salmon hatchery from which they released ca. one million Chinook salmon smolts on May 12 and May 18, 2023. WWU student researchers within the Marine Mammal Ecology Lab observed harbor seals daily prior to and after the releases at dawn and dusk along the Whatcom Waterway to examine seal responses to the out-migrating smolt. Observations were divided as prior to release (A: 8-12 May), in-between releases (B: 13-18 May) and post-releases (C: 19-31 May). There was an increase in the maximum daily number of harbor seals swimming along the waterway after smolt were released, particularly at dusk (A: avg= 2.4 seals, SD= 0.55, n= 5 days; B: avg= 4.7, SD= 1.5, n= 6; C: avg= 4.2, SD= 1.1, n= 13). Further, there was an increase in hunting events per seal (A: avg= 0 events, SD= 0, n= 5 days; B: avg= 0.53, SD= 0.81, n= 6; C: avg= 0.46, SD= 1.29, n= 13). Of note, at least 10 other species of predators fed on the smolt, including great blue heron (Ardea herodias), osprey (Pandion haliaetus), and river otters (Lontra canadensis). Preliminary results indicate that harbor seals were attracted to the release of smolt in the Whatcom Waterway. However, the presence of many other predators suggests that assessing the impact of pinnipeds on the recovery of Chinook salmon requires incorporating the contribution of other predators. (Because this paper has been submitted for publication ...