Pacific harbor seal (Phoca vitulina richardii) monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area: 2016 annual report

Codde, Sarah; Allen, 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 2016 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 assisted NPS staff in completing 265 surveys at eight Marin County sites, contributing approximately 465 hours of monitoring. During the breeding season, a peak count of 2,126 adult and immature seals was recorded at all Marin County monitoring sites, which is less than the 16-year average and one of the lowest counts recorded. The Drakes Estero Complex had the most adult and immature seals (473), followed by Tomales Bay (437). During the breeding season, 951 seal pups were recorded at all Marin County sites, which is also less than the 16-year average. The Drakes Estero Complex and Double Point accounted for 58% (552) of pups at Marin County haul-outs. During the molting season, a peak count of 3,722 animals was recorded at Marin County sites, which is similar to the 16-year average. During the 2016 monitoring seasons, 101 disturbances to seals were recorded. The most frequent causes were humans on foot (26%), unknown sources (23%), and motor boats (21%). Thirteen regional surveys were conducted throughout the breeding and molting seasons at locations in Sonoma, Marin and San Mateo counties, and San Francisco Bay. Of these areas, Marin County sites accounted for 55% of breeding season adult and immature animals (2,080 of 3,759), 71% of pups (908 of 1,274), and 65% of seals during the molting season (3,606 of 5,580), 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: 2016 annual report

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