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Winter surveys at the Channel Islands and Point Conception reveal population growth of northern elephant seals and residence counts of other pinnipeds
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    Winter surveys of the Channel Islands and Point Conception were conducted during 2002-2018 to (1) derive estimates of northern elephant seal (Mirounga angustirostris) births for estimating population growth rates and abundance, (2) estimate pre-census pup mortality for mid-to-late February surveys, (3) document breeding season abundance and distribution of elephant seals, and (4) document non-breeding season abundance and distribution of California sea lions (Zalophus californianus), Pacific harbor seals (Phoca vitulina), Steller sea lions (Eumetopias jubatus), and northern fur seals (Callorhinus ursinus). Data were obtained from ground counts conducted at San Clemente Island during 2002-2015 and 2017-2018, and from aerial photographic surveys conducted at all Channel Islands and Point Conception in 2005, 2010, and 2013. Northern elephant seal births were estimated from (1) counts of live plus dead pups, or (2) by applying the 97.5% fecundity rate of Año Nuevo rookery to counts of adult females or to estimates of the asynchronous population of adult females derived from multiple breeding season surveys conducted at the three largest Channel Islands rookeries during January, February, and March at San Nicolas Island in 2010, and at San Miguel, San Nicolas, and Santa Rosa Islands in 2013. Pre-census pup mortality was estimated for mid-to-late February surveys because they could be applied to previous surveys made during that time and because multiplesurveys are too costly to conduct for the Channel Islands (making it likely that single mid-to-late February surveys will be conducted in the future). Pre-census pup mortality for the mid-to-late-February surveys was higher in 2010 (7.1%) than it was in 2013 (2.7% to 3.6%). Multipliers for estimating pre-census pup mortality from dead pups counted in mid-to-late February surveys ranged from 2.40 to 3.36, with a 2013 mean multiplier of 2.93. Multipliers converted dead pup counts from mid-to-late-February surveys into an estimate of total pre-census pup mortality, then added to the count of live pups to estimate total births. Elephant seal birth estimates indicated that the population at the Channel Islands increased at an average annual rate of 3.1% during 1989-2013 with an abundance of 153,387 (95%CI: 132,509 to 175,506) individuals in 2013. San Miguel, San Nicolas, and Santa Rosa Islands accounted for 99.6% to 99.8% of elephant seal births at the Channel Islands. During 2013 surveys, California sea lions were found at all of the Channel Islands, and Pacific harbor seals were found at all islands except Anacapa and Santa Catalina Islands. Steller sea lions were found at San Miguel, Anacapa, and San Clemente Islands, and northern fur seals were found only at San Miguel Island.
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