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Seasonal changes in the distribution and abundance of pacific harbor seals (Phoca vitulina richardii) in South Humboldt Bay, California and its newly enacted marine protected area
Harbor seals have been listed as a species likely to benefit from new Marine Protected Areas (MPAs) in California as part of the Marine Life Protection Act. Whereas seals may experience direct and indirect effects from these MPAs as a whole, the impacts of individual MPAs remains unclear. To support the analysis of the impacts of one new MPA located in South Humboldt Bay (SHB), California, I conducted two studies to measure the site fidelity of individual harbor seals within SHB and to describe the changes in distribution and abundance of hauled-out seals inside and outside the new MPA there. From June 2011 through May 2012, I used radio telemetry to assess site fidelity of 28 individually tagged seals. Most seals had high fidelity (>75%) for SHB haul-outs, indicating that these seals are present enough to potentially benefit from added protection. However, the use of radio telemetry proved difficult and costly for long-term data collection. Therefore, weekly visual surveys were implemented beginning in July 2012 to track the habitat use of all seals hauled-out in SHB. There were significant seasonal differences in seal abundance (ANOVA, F5 = 4.047, p < 0.01) and groupings (ANOVA, F5 = 10.06, p <0.01), particularly between the winter and the spring seasons. In addition to highlighting key seasons for additional management and monitoring, these surveys proved more successful and sustainable than radio telemetry for monitoring year-round impacts of the new MPA on harbor seals.