Abstract
Reductions in sea ice and increases in air and seawater temperatures have been documented in the Arctic, making female Pacific walruses (Odobenus rosmarus divergens) vulnerable to changes in foraging, energy budgets, and reproductive fitness. The aim of the present study was to assess how walrus reproductive capacity has changed over a span of 35 years analyzing ovaries from three distinct time frames: 1975, 1994 to 1999 and 2008 to 2010. Ovarian weights and volumes, corpora lutea diameter, total number of corpora lutea and albicantia, and the percent of females ovulating in their current cycle were used to evaluate reproductive capacity. Ovaries were collected from walruses hunted by Alaska Native communities for subsistence purposes. There were no differences in ovarian weights or percent of quiescent females between 1975 and 2008 to 2010. Ovaries from 1994 to 1999 were significantly heavier, exhibited more corpora, and all females from this time frame were ovulating at the time of harvest. Reproductive capacity was limited during 1975, due to known density-dependent stressors; reproductive capacity increased during 1994–1999, as harvests increased and more resources became available, and in 2008–2010, females were as reproductively limited as those of 1975. The cause for this reduction in reproductive capacity is unknown, but maybe a result of multiple factors, including an increase in population size coincident with a decrease in carrying capacity, and cumulative stressors relating to sea ice loss, contaminants, and anthropogenic impacts.
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Acknowledgements
All samples were collected by USFWS in accordance with Federal regulations 50 CFR 18.23(b) (2). This work would not have occurred without the Bering Strait island communities of Diomede, Gambell and Savoonga providing walrus specimens from their subsistence hunts and we thank them. Additional walrus specimens (spanning the 2008–2010 time frame) were graciously provided by Jonathan Snyder of USFWS, Alan Springer, and Suzann Speckman. We thank our collaborators at the University of Alaska Museum of the North, especially Link Olson and Aren Gunderson, USFWS and the Eskimo Walrus Commission. We acknowledge the contributions from colleagues Gordon Kruse, Gay Sheffield and John Burns, as well as Philip Ganz and Wendel Raymond for assistance in statistical analyses and figure preparation, and Anatoloy Kochnev for kindly sharing his research. This manuscript was improved by the helpful comments of R. Stimmelmayr, J. Gilbert and an anonymous reviewer. Funding was provided by the North Pacific Research Board Graduate Research Award, the Resilience and Adaptation Program at the University of Alaska Fairbanks, the Rasmuson Fisheries Science Center, Alaska EPSCoR and the Erich Follman Memorial Student Research Support.
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300_2020_2693_MOESM1_ESM.xlsx
University of Alaska Museum of the North accession numbers of Pacific walrus (Odobenus rosmarus divergens) ovary samples from three time frames: 1975, 1994-99, and 2008–2010. Ages and harvest dates were provided by the Alaska Department of Fish and Game (1975) and US Fish and Wildlife Service (1994–1999 and 2008–2010). Supplementary file1 (XLSX 19 kb)
300_2020_2693_MOESM2_ESM.xlsx
Summary statistics comparing corpora counts in Pacific walrus (Odobenus rosmarus divergens) ovaries sampled in 1994–1999 in the present study with corpora counts conducted in a previous study published by Garlich-Miller 1997. Supplementary file2 (XLSX 10 kb)
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Larsen Tempel, J.T., Atkinson, S. Pacific walrus (Odobenus rosmarus divergens) reproductive capacity changes in three time frames during 1975–2010. Polar Biol 43, 861–875 (2020). https://doi.org/10.1007/s00300-020-02693-4
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DOI: https://doi.org/10.1007/s00300-020-02693-4