Pacific Harbor Seal (Phoca vitulina richardii) Monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area: 2021 Annual Report

Codde, Sarah; Allen, Sarah

doi:10.36967/2315873

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. The objectives of monitoring each site and the population as a whole are to: i) detect changes in population size, ii) detect changes in reproductive success as indicated by pup production, and iii) identify anthropogenic or environmental factors, including climate change, that may affect the condition of the population (Adams et al. 2009). Members of the Harbor Seal Monitoring Volunteer Program and NPS staff conducted 172 harbor seal surveys throughout the 2021 breeding and molting seasons (March–May and June–July, respectively) once or twice per week 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 count of adult and immature seals we recorded at all Marin County monitoring sites was 2,107 seals, which is below the 20-year average and is one of the lowest counts on record during the NPS study period. During the breeding season, we recorded 972 seal pups at all Marin County sites, which is slightly less than the 20-year average. During the molting season, volunteers and staff recorded 2,581 seals as the peak count for all Marin County sites, which is much lower than the 20-year average and is the lowest count on record during the study period. During the monitoring surveys, we recorded 38 disturbances to seals. The most frequent causes were unknown sources (29%) and motorboats (26%). Coyotes became a primary source of disturbance at Drakes Estero in 2021, and staff and volunteers witnessed predation of harbor seal pups. Members of the Central California Regional Harbor Seal Monitoring Program (which includes NPS staff and volunteers) conducted thirteen regional surveys throughout the breeding and molting seasons at locations in San Francisco Bay and Mendocino, Sonoma, Marin, and San Mateo counties. Of these areas, Marin County sites accounted for 62% of breeding season adult and immature animals (2,093 of 3,399), 71% of pups (972 of 1,365), and 60% of seals during the molting season (2,369 of 3,970), all of which are similar proportions to past years.

Pacific Harbor Seal (Phoca vitulina richardii) Monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area: 2021 Annual Report

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