Trends and status of harbor seals in Washington State (1978-2019) with management applications

• Main Author: Pearson, Dr. Scott
• Format: Text
• Language: English
• Published: Western CEDAR 2022
• Subjects: harbor seal; Phoca vitulina
• Online Access: https://cedar.wwu.edu/ssec/2022ssec/allsessions/210; https://cedar.wwu.edu/context/ssec/article/3372/type/native/viewcontent/Harbor_20Seal_20Stock_20Asessment_SEC_20Conference.pptx_AWSAccessKeyId_AKIAYVUS7KB2I6J5NAUO_Signature_gPU7rGQ8UtFJPhSAPHv2KboS5xA_3D_Expires_1690453762

Harbor seal (Phoca vitulina richardsi) numbers were severely reduced in Washington by a federally-financed control program in the first half of the twentieth century. Seal numbers rebounded after the cessation of bounties and the establishment of legal protections under the Marine Mammal Protection Act of 1972 (MMPA). As seal and sea lion populations recover, updated stock estimates are critical for determining their status under the MMPA, assessing management options under the Act, and for modelling exercises designed to evaluate the role of pinnipeds in marine ecosystems. To estimate population size and abundance trends in Washington State, we conducted aerial surveys of harbor seal haulout sites between 1975 and 2019. From these data, we derived stock estimates for: 1) Hood Canal, 2) Southern Puget Sound, 3) Northern Inland, and 4) the Washington portion of the Washington-Oregon coastal stock. Generalized logistic population growth curves were fitted to all stocks except for Hood Canal where we had insufficient comparable data prior to 1991 to fit a population growth curve. Other than Hood Canal, the population size estimates for the inland waters and coastal Washington stocks were above maximum net productivity level, thus we conclude that they are within their optimal sustainable population range under the MMPA. We explain how this information can be used to inform seal population management under the MMPA and demonstrate how these estimates can be used in bioenergetics models to assess the impacts of seals on Puget Sound Chinook and coho salmon.