Pacific harbor seal (Phoca vitulina richardii) monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area: 2019 monitoring season

Codde, Sarah

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). Harbor seal surveys were conducted throughout the 2019 breeding and molting seasons (March-May and June-July, respectively) once or twice per week at the largest Point Reyes National Seashore and Golden Gate National Recreation Area harbor seal colonies, collectively referred to as Marin County sites. Members of the Harbor Seal Monitoring Volunteer Program and NPS staff completed 190 surveys at eight Marin County sites, contributing approximately 329 hours of monitoring. During the breeding season, the peak count of adult and immature seals recorded at all Marin County monitoring sites was 2,456 seals, which is slightly less than the baseline average (data from 2000 – 2015). The Drakes Estero Complex had the highest peak number of adult and immature seals (675), followed by Tomales Bay (434) and Bolinas Lagoon (408). During the breeding season, 1,106 seal pups were recorded at all Marin County sites, which is similar to the baseline average. The Drakes Estero Complex, Bolinas Lagoon, and Double Point accounted for the majority of pups at Marin County haul-outs in 2019. During the molting season, the peak count recorded at Marin County sites was 2,961 seals, which is lower than the baseline average and is one of the lowest counts on record in the 20-year study period. During the monitoring surveys, 62 disturbances to seals were recorded. The most frequent causes were motorboats (26%), humans on foot (24%), and unknown sources (21%). Thirteen regional surveys were conducted throughout the breeding and molting seasons at locations in San Francisco Bay and Sonoma, Marin and San Mateo counties. Of these areas, Marin County sites accounted for 60% of breeding season adult and immature animals (2,416 of 4,015), 73% of pups (1,103 of 1,503), and 63% of seals during the molting season (2,839 of 4,526), 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: 2019 monitoring season

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