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Variability in temporary emigration rates of individually marked female Weddell seals prior to first reproduction

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In many species, temporary emigration (TE) is a phenomenon, often indicative of life-history characteristics such as dormancy, skipped reproduction, or partial migration, whereby certain individuals in a population are temporarily unobservable at a particular site. TE may be a flexible condition-dependent strategy that allows individuals to mitigate effects of adverse conditions. Consequently, TE rates ought to be highly variable, but sources of variations are poorly understood for most species. We used data from known-aged female Weddell seals (Leptonychotes weddellii) tagged in Erebus Bay, Antarctica, to investigate sources of variation in TE rates prior to reproduction and to evaluate possible implications for age-specific probability of first reproduction. TE rates were near 1 the year after birth, decreased to an average of 0.15 (\( \widehat{\text{SE}} \) = 0.01) by age 8, and were similar thereafter. TE rates varied substantially from year-to-year and were lower for seals that attended reproductive colonies the previous year than for seals that did not attend (e.g., \( \overline{{\hat{\psi }_{{i,{\text{age}}\,8}}^{\text{UU}} - \hat{\psi }_{{i,\,{\text{age}}\,8}}^{\text{PU}} }} \) = 0.22). Recruitment rates were marginally greater for seals that did attend than for seals that did not attend colonies the previous year. For Weddell seals specifically, our results suggest that (1) motivation to attend colonies varied temporally, (2) as seals grew older they had increased motivation to attend even before reproductive maturity, and (3) seals appear to follow various attendance strategies. More broadly, our results support the idea of TE as a variable, condition-dependent strategy, and highlight the utility of TE models for providing population and life-history insights for diverse taxa.

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This work was supported by the National Science Foundation, Office of Polar Programs (grant no. ANT-0635739 to R.A. Garrott, J.J. Rotella, and D.B. Siniff, and previous grants to D.B. Siniff and J.W. Testa). Animal handling protocol was approved by Montana State University’s Institutional Animal Care and Use Committee (Protocol #41-05) and complied with the Marine Mammal Permit Act of the USA and the multinational Antarctic Conservation Act. Raytheon Polar Services Corporation, Petroleum Helicopters International, and the New York National Guard provided logistical support for field work in Antarctica. We thank D.B. Siniff for numerous conversations about Weddell seal ecology and helpful advice throughout this work, W.L. Kendall for advice on analysis and critical review of previous manuscript drafts, and J.L. Laake for help with RMark coding. We appreciate the dozens of field assistants that supported this project through the years. Two anonymous reviewers provided helpful comments on an earlier manuscript draft.

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Correspondence to Glenn E. Stauffer.

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Communicated by Helene Marsh.

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Stauffer, G.E., Rotella, J.J. & Garrott, R.A. Variability in temporary emigration rates of individually marked female Weddell seals prior to first reproduction. Oecologia 172, 129–140 (2013).

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