Abstract: We report on the distribution and abundance of the northern elephant seal (Mirounga angustirostris) in the United States from 1991 to 2010. Pup production (i.e., births) was the principal metric used to characterize abundance, distribution, and popu-lation growth of the U.S. population and of each rookery in the U.S. Birth estimates were obtained from the literature and estimated from recent counts of adult females or counts of pups made during ground and aerial photographic surveys conducted during the pupping-breeding season at all rookeries in central California and the Channel Islands in southern California. A total of 40,684 pups were estimated to have been born at 11 rookeries in the U.S. in 2010. The two most productive rookeries as of 2010 were San Miguel Island (16,208 pups) and San Nicolas Island (10,882 pups). The Piedras Blancas rookery was not established in 1991 but has since grown to be the fourth largest rookery as of 2010. Rookeries grew most rapidly initially, presumably due to high immigration rates; then increased moderately, eventually becoming stable; and some declined in size. Since 1988, the U.S. population has been growing at an average annual rate of 3.8%. The multiplicative factor needed to estimate total population size from pup production is estimated at 4.4. Total U.S. population size in 2010 was estimated at 179,000 individuals. Using conservative estimates for population growth of northern elephant seals in Mexico, we estimate that the total population in Mexico and the U.S. in 2010 was between 210,000 and 239,000 individuals.
Key Words: population growth, marine mammal census, pinniped, northern elephant seal, Mirounga angustirostris
Document Type: Research article
DOI: 10.1578/AM.40.1.2014.20
Page Numbers: 20-31

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