Movements and Home Ranges of Harbor Seals (Phoca vitulina) in the Inland Waters of the Pacific Northwest

• Main Author: Hardee, Sarah E.
• Format: Text
• Language: unknown
• Published: Western Washington University 2008
• Subjects: Pacific; San Juan; harbor seal; Phoca vitulina
• Online Access: https://dx.doi.org/10.25710/n92x-0g80; https://cedar.wwu.edu/wwuet/9

Marine resources are under increasing human pressure and conservation managers are using tools such as marine reserves to increase target fish stocks. However, marine predators may respond to the resultant changes in fish abundance. Harbor seals, Phoca vitulina, are abundant marine predators in the inland waters of the Pacific Northwest with the potential to influence the recovery of depressed fish stocks, yet relatively little is known about their movement patterns and home range sizes in the region. To describe harbor seal behavior, I deployed satellite and time-depth recorder tags during April and May 2007 on 20 individuals at three haul-out sites in the inland waters of the Pacific Northwest: six at a rocky reef site in the eastern San Juan Islands, six at an estuarine bay site directly east of the San Juan Islands and eight at a rocky reef site in the Canadian Gulf Islands. Tags were deployed for a mean (± SD) of 110 (± 32) d and transmitted a mean 726 (± 382) satellite locations seal-1. Satellite locations allowed me to quantify distances moved from the capture site, minimum convex polygon size, home range size, utilization of candidate marine reserve sites in the eastern San Juan Islands and haul-out site fidelity. This study used novel analysis techniques, including weighting satellite transmissions to account for autocorrelation within the data to calculate harbor seal home ranges using fixed kernel density estimates. Overall, harbor seals moved farther than previously documented in the region and their behavior, including distance traveled, home range size and haul-out site fidelity, appeared to be influenced by haul-out site. There was no effect of month or season on the behavior of the harbor seals. Harbor seals from the rocky reef sites moved farther distances for longer periods of time and utilized haul-outs over a wider geographic distribution than seals from the bay site. Three individuals from the rocky sites traveled to the Pacific coast of Washington and British Columbia and then returned one to two months later, a roundtrip distance > 200 km. Additionally, seals from the rocky reef haul-outs had segmented home ranges, with core areas of use up to 100 km apart. Despite moving greater distances than previously estimated within the region, harbor seals rarely utilized the space within candidate marine reserves. Less than 4.5 % of all satellite transmissions fell < 3 km from the boundaries of the reserves. It is likely that harbor seals from rocky reef haul-outs moved greater distances than previously assumed in search of prey. The long-distance movements of tagged individuals suggest that seals from distant haul-outs could visit candidate marine reserves in the eastern San Juan Islands, consequently increasing the pool of predators that could potentially impact such sites. Combining these observations with synchronous diet and diving behavior analyses will provide comprehensive baseline behavior, which will allow us to determine how harbor seals interact with the recovery of target fish species within the inland waters of the Pacific Northwest.