Pacific Harbor Seal (Phoca vitulina richardii) Monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area: 2022–2023 Report

Codde, Sarah; Allen, Sarah

doi:10.36967/2319399

Pacific harbor seals (Phoca vitulina richardii) are the most abundant and only year-round resident pinniped in the National Parks of the San Francisco Bay Area, California. Annual monitoring by National Park Service (NPS) staff, using peer-reviewed methods, began in 1996 with the current suite of monitoring sites adopted in 2000. Members of the Harbor Seal Monitoring Volunteer Program, Marin County Parks staff, and NPS staff conducted 183 harbor seal surveys throughout the 2022 breeding and molting seasons (March–May and June–July, respectively) and 203 surveys throughout the 2023 seasons at the eight largest Point Reyes National Seashore and Golden Gate National Recreation Area harbor seal colonies, collectively referred to as Marin County sites. During the breeding season, the peak counts of adult and immature seals we recorded at all Marin County monitoring sites were 2,083 seals in 2022 and 1,599 seals in 2023, which were both below the 21-year average and were the lowest counts on record during the NPS study period. We also recorded 930 seal pups at all Marin County sites in 2022 and 912 pups in 2023, both of which were less than the 21-year average. During the molting season, the peak counts we recorded at Marin County sites were 2,374 seals in 2022 and 2,270 seals in 2023, which were both much lower than the 21-year average and the lowest counts on record during the study period. During the monitoring surveys, we recorded 67 disturbances to seals in 2022 and 80 disturbances in 2023. In 2022, the most frequent causes were humans on foot (28%) and birds (22%). In 2023, the most frequent causes were unknown sources (30%) and birds (20%). Members of the Central California Regional Harbor Seal Monitoring Program (which includes NPS staff and volunteers) conducted regional surveys throughout the breeding and molting seasons at locations in San Francisco Bay and Mendocino, Sonoma, Marin, and San Mateo counties. In 2022, Marin County sites accounted for 64% of breeding season adult and immature animals, 72% of pups, and 58% of seals during the molting season, all of which were similar proportions to past years. In 2023, Marin County sites accounted for 56% of breeding season adult and immature seals, 73% of pups, and 55% of seals during the molting season, all of which were similar to proportions in past years except the breeding season adult and immature proportion which was lower than normal.

Pacific Harbor Seal (Phoca vitulina richardii) Monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area: 2022–2023 Report

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