Pacific harbor seal (Phoca vitulina richardii) monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area: 2015 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. Long-term monitoring studies at the largest harbor seal colonies in Point Reyes National Seashore have been conducted intermittently since the mid-1970s by various groups. 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 2015 breeding and molting seasons (March-May and June-July, respectively) once to 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 253 surveys at eight Marin County sites, contributing approximately 450 hours of monitoring. During the breeding season, a peak count of 2,696 adult and immature seals was recorded at all Marin County monitoring sites, which is the same as the 15-year average. The Drakes Estero Complex had the most adult and immature seals (839), followed by Tomales Bay (460) and Double Point (442). During the breeding season, 1,051 seal pups were recorded at all Marin County sites, which is similar to the 15-year average. The Drakes Estero Complex and Double Point accounted for 59% (617) of pups at Marin County haul-outs. During the molting season, a peak count of 4,230 animals was recorded at Marin County sites, which is similar to the 15-year average. During surveys, 89 disturbances to seals were recorded. The most frequent causes were unknown source (25%) and humans on foot (18%). 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 62% of breeding season adult and immature animals (2,659 of 4,271), 76% of pups (1,193 of 1,613), and 66% of seals during the molting season (3,738 of 5,688), 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: 2015 annual report

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