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Mark-recapture modeling accounting for state uncertainty provides concurrent estimates of survival and fecundity in a protected harbor seal population

Authors

  • Line S. Cordes,

    Corresponding author
    1. University of Aberdeen, Institute of Biological and Environmental Sciences, Lighthouse Field Station, Cromarty IV11 8YL, United Kingdom
    Current affiliation:
    1. Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, Colorado 80523, U.S.A
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  • Paul M. Thompson

    1. University of Aberdeen, Institute of Biological and Environmental Sciences, Lighthouse Field Station, Cromarty IV11 8YL, United Kingdom
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Abstract

Harbor seal breeding behavior and habitats constrain opportunities for individual-based studies, and no current estimates of both survival and fecundity exist for any of the populations studied worldwide. As a result, the drivers underlying the variable trends in abundance exhibited by harbor seal populations around the world remain uncertain. We developed an individual-based study of harbor seals in northeast Scotland, whereby data were collected during daily photo-identification surveys throughout the pupping seasons between 2006 and 2011. However, a consequence of observing seals remotely meant that information on sex, maturity-stage, or breeding status was not always available. To provide unbiased estimates of survival rates we conditioned initial release of individuals on the first time sex was known to estimate sex-specific survival rates, while a robust design multistate model accounting for uncertainty in breeding status was used to estimate reproductive rate of multiparous and ≥3-yr-old females. Survival rates were estimated at 0.95 (95% CI = 0.91–0.97) for females and 0.92 (0.83–0.96) for males, while reproductive rate was estimated at 0.89 (0.75–0.95) for multiparous and 0.69 (0.64–0.74) for ≥3-yr-old females. Stage-based population modeling indicated that this population should be recovering, even under the current shooting quotas implemented by the recent management plan.

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