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Disentangling the cause of a catastrophic population decline in a large marine mammal

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https://ir.library.oregonstate.edu/concern/articles/hq37vq147

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  • Considerable uncertainties often surround the causes of long-term changes in population abundance. One striking example is the precipitous decline of southern sea lions (SSL; Otaria flavescens) at the Falkland Islands, from 80 555 pups in the mid 1930s to just 5506 pups in 1965. Despite an increase in SSL abundance over the past two decades, the population has not recovered, with the number of pups born in 2014 (minimum 4443 pups) less than 6% of the 1930s estimate. The order-of-magnitude decline is primarily attributed to commercial sealing in Argentina. Here, we test this established paradigm and alternative hypotheses by assessing (1) commercial sealing at the Falkland Islands, (2) winter migration of SSL from the Falkland Islands to Argentina, (3) whether the number of SSL in Argentina could have sustained the reported level of exploitation, and (4) environmental change. The most parsimonious hypothesis explaining the SSL population decline was environmental change. Specifically, analysis of 160 years of winter sea surface temperatures revealed marked changes, including a period of warming between 1930 and 1950 that was consistent with the period of SSL decline. Sea surface temperature changes likely influenced the distribution or availability of SSL prey and impacted its population dynamics. We suggest that historical harvesting may not always be the “smoking gun” as is often purported. Rather, our conclusions support the growing evidence for bottom-up forcing on the abundance of species at lower trophic levels (e.g., plankton and fish) and resulting impacts on higher trophic levels across a broad range of ecosystems.
  • This is the publisher’s final pdf. The published article is copyrighted by Ecological Society of America and can be found at: http://www.esajournals.org/loi/ecol
  • Keywords: killer whales, megafaunal collapse, historical baselines, South Atlantic, pinniped, Orcinus orca, top-down control, ocean climate, bottom-up forcing
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  • Baylis, A. M., Orben, R. A., Arnould, J. P., Christiansen, F., Hays, G. C., & Staniland, I. J. (2015). Disentangling the cause of a catastrophic population decline in a large marine mammal. Ecology, 96(10), 2834-2847. doi:10.1890/14-1948.1.sm
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  • 96
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  • 10
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  • A. M. M. Baylis and I. J. Staniland received funding from the Darwin Initiative and Project AWARE for PTT deployments. A. M. M. Baylis received funding from the Shackleton Scholarship Fund (Centenary Award), Rufford Small Grants, Sea World and Busch Gardens Conservation Fund, Joint Nature Conservation Council, and the Falkland Islands Government for the 2014 census. A. M. M. Baylis also gratefully acknowledges funding received from National Geographic and the Winnifred Violet Scott Charitable Trust. Research was conducted under permits R14/2011 and R14/2013 issued by the Falkland Islands Government.
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file details OrbenRachaelFishWildlifeDisentanglingCauseCatastrophic.pdf 07/26/2017 Public
file details OrbenRachaelFishWildlifeDisentanglingCauseCatastrophicAppendix A.pdf 07/26/2017 Public
file details OrbenRachaelFishWildlifeDisentanglingCauseCatastrophicAppendix B.pdf 07/26/2017 Public
file details OrbenRachaelFishWildlifeDisentanglingCauseCatastrophicAppendix C.pdf 07/26/2017 Public