Breeding season distribution and population grow of California sea lions, Zalphus californianus, in the United States druing 1964-2014
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Breeding season distribution and population grow of California sea lions, Zalphus californianus, in the United States druing 1964-2014
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    Breeding-season distribution and population growth rate of California sea lions (Zalophus californianus) in the U.S. population are estimated from counts of pups and non-pups collected during 1964 to 2014. Pup and non-pup count data were compiled from published and unpublished sources. These data showed that during this period the U.S. count of live-pups increased at an average annual rate of 4.7% per year (L95% CI=4.2%, U95% CI=5.2%). Average annual growth rates of live-pup counts at the four main island-rookeries in southern California (Santa Barbara Island, San Clemente Island, San Nicolas Island, and San Miguel Island; hence fore referred to as the Main Channel Islands) ranged from 4.2% to 5.5% from 1964 to 2014. The Channel Islands count of non-pups (non-pup counts were unavailable for the entire U.S. population prior to 2003) increased at an average annual growth rate of 2.8% per year (L95% CI=2.4%, U95% CI=3.4%). San Nicolas Island and San Miguel Island were the largest rookeries in the U.S. population, both having the most pups and non-pups. Prior to 1990, 59.2% of live pups counted in the Channel Islands were on San Miguel Island, and 32.4% were on San Nicolas Island. After 1990, these islands constituted 44.9% and 45.6% of Channel Island pups, respectively. California-wide surveys conducted during 2003-2005, 2007, and 2011-2013 indicated that the Main Channel Islands rookeries accounted for 99.71% of live pups counted in California and 77.35% of hauled-out non-pups in California during the breeding season. Sea lion counts were modeled (using generalized linear modeling) as a function of sea level height at Los Angeles, California (SLH-LA), Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO), and Multivariate El Niño Index (MEI). This model indicated that more pups were produced during cold-water conditions and fewer pups were produced during warmwater conditions, and that fewer non-pups were present at southern California rookeries during warm-water conditions and more were present during cold-water conditions.
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