Northern Elephant Seal Monitoring 2005-2007 Report, Point Reyes National Seashore.

Adams, Dawn

Northern elephant seals (Mirounga angustirostris) established a breeding population at Point Reyes National Seashore (PORE) in 1981 after near extirpation from North America. Currently, elephant seals breed at three sites in PORE including Drake’s Beach (NDB), Point Reyes Headland (PRH), and South Beach (SB). In response to the increase of the breeding population of seals and associated park activities, PORE began to monitor the elephant seal population to contribute to the understanding of population changes and management needs, and to develop research, interpretation and enforcement strategies. During December to March of each breeding season, we conducted a complete census a minimum of once per week at all breeding sites. In 2006, 20 complete censuses were done and 26 in 2007. Each season, we applied flipper tags to weaned pups, and conducted weekly surveys to resight tagged animals. Reproductive productivity index was estimated as the number of pups compared to number of adult females. Using a correction factor, we estimated a total population size of 2,100 and 2,285 seals at PORE in 2005 and 2006, respectively. Almost 50% more females were counted at NDB colony sites in 2006 (223) compared with 2005 (147). There also was a smaller increase of 20% at NDB in 2007 (272). We suspect that due to hazardous coastal weather and tide conditions coinciding with the initial arrival of females, NDB became a more attractive colony site than PRH in 2006. The other colony sites, PRH and SB, showed much smaller increases in numbers of female seals (10% and 20% respectively) in 2006 and declines (-13% and -30%) in 2007, indicating movement from these sites to NDB. During the 2006 season, a total of 225 elephant seal pups were tagged. In 2007, we tagged 232 weaned pups and two sub-adult males. In 2006, 63 seals were resighted (78 tag observations) with tags originally applied at PORE. In 2007, 78 seals were resighted (103 tag observations) as PORE seals. The highest proportion of seals resighted were females, followed by multiple age classes of males, then yearlings and weaned pups. A total of 36 elephant seals (46 tag observations) originally tagged at other colonies were documented at PORE breeding sites during the 2006 season; and 32 seals (39 tag observations) were resighted during the 2007 breeding season. The overall population productivity index was 0.82 in 2006 and 0.93 in 2007. Since 2005, there has been a slightly greater increase in productivity at the more recently colonized sites (NDB, SB) compared with the remote PRH site. Reduction of human disturbance through park-implemented signage, increased law enforcement near colonies, a docent program and greater public awareness has likely contributed to the successful establishment of these peripheral sites.

Northern Elephant Seal Monitoring 2005-2007 Report, Point Reyes National Seashore.

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