Abstract
AbstractTranslocation and rehabilitation programmes are critical tools for wildlife conservation. These methods achieve greater impact when integrated in a combined strategy for enhancing population or ecosystem restoration. During 2002–2016 we reared 37 orphaned southern sea otter Enhydra lutris nereis pups, using captive sea otters as surrogate mothers, then released them into a degraded coastal estuary. As a keystone species, observed increases in the local sea otter population unsurprisingly brought many ecosystem benefits. The role that surrogate-reared otters played in this success story, however, remained uncertain. To resolve this, we developed an individual-based model of the local population using surveyed individual fates (survival and reproduction) of surrogate-reared and wild-captured otters, and modelled estimates of immigration. Estimates derived from a decade of population monitoring indicated that surrogate-reared and wild sea otters had similar reproductive and survival rates. This was true for males and females, across all ages (1–13 years) and locations evaluated. The model simulations indicated that reconstructed counts of the wild population are best explained by surrogate-reared otters combined with low levels of unassisted immigration. In addition, the model shows that 55% of observed population growth over this period is attributable to surrogate-reared otters and their wild progeny. Together, our results indicate that the integration of surrogacy methods and reintroduction of juvenile sea otters helped establish a biologically successful population and restore a once-impaired ecosystem.
Highlights
W ildlife conservation may involve management interventions to achieve both population and ecosystem goals
Hazards associated with age and sex differences varied among all study groups, resulting in inverted-U shape survival curves that are typical for sea otters and other large mammals (Fig. ; Tinker et al, )
The surrogacy methods we used allowed naïve juveniles to be successfully returned to the wild with survival (Fig. ) and reproductive rates (Table ) similar to the native population
Summary
W ildlife conservation may involve management interventions to achieve both population and ecosystem goals. One type of conservation intervention, translocation, has become an important tool for rebuilding the abundance, expanding the geographical range, and improving the genetic diversity of wild populations For critically-reduced, dispersallimited, or highly fragmented populations, translocation is among the most effective methods to rebuild populations (Sarrazin & Barbault, ; Fischer & Lindenmayer, ). In addition to recovering populations, translocation may help to restore degraded ecosystems. Reestablishing key grazers or top predators, for example, can restore important ecological functions that are critical to ecosystem health (Berger et al, ; Beschta & Ripple, ; Seddon et al, ). The conservation benefits of translocation are often clear, its implementation may be challenging
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