PMID: 18213964Jan 25, 2008Paper

Age-structured modeling reveals long-term declines in the natality of western Steller sea lions

Ecological Applications : a Publication of the Ecological Society of America
E E HolmesK Sweeney

Abstract

Since the mid-1970s, the western Steller sea lion (Eumetopias jubatus), inhabiting Alaskan waters from Prince William Sound west through the Aleutian Islands, has declined by over 80%. Changing oceanographic conditions, competition from fishing operations, direct human-related mortality, and predators have been suggested as factors driving the decline, but the indirect and interactive nature of their effects on sea lions have made it difficult to attribute changes in abundance to specific factors. In part, this is because only changes in abundance, not changes in vital rates, are known. To determine how vital rates of the western Steller sea lion have changed during its 28-year decline, we first estimated the changes in Steller sea lion age structure using measurements of animals in aerial photographs taken during population surveys since 1985 in the central Gulf of Alaska (CGOA). We then fit an age-structured model with temporally varying vital rates to the age-structure data and to total population and pup counts. The model fits indicate that birth rate in the CGOA steadily declined from 1976 to 2004. Over the same period, survivorship first dropped severely in the early 1980s, when the population collapsed, and then survivor...Continue Reading

References

Sep 16, 1994·The Science of the Total Environment·R J Norstrom, D C Muir
Jun 11, 2002·Marine Environmental Research·A AguilarP J Reijnders
Jun 27, 2003·The Science of the Total Environment·Mace G BarronMargaret M Krahn
Oct 4, 2003·Proceedings of the National Academy of Sciences of the United States of America·A M SpringerB Pfister
May 23, 2006·Ecological Applications : a Publication of the Ecological Society of America·Daniel Hennen

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Citations

May 20, 2009·Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences·J A EstesT M Williams
Mar 7, 2009·Ecological Applications : a Publication of the Ecological Society of America·Nicholas Wolf, Marc Mangel
Jun 14, 2012·Ecology·Mark S Udevitz, Peter J P Gogan
Sep 23, 2009·Ecological Applications : a Publication of the Ecological Society of America·Michelle E LanderLowell W Fritz
Apr 3, 2013·The Science of the Total Environment·Lorrie D ReaTodd M O'Hara

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