Assessing anthropogenic risk to sea otters for reintroduction into San Francisco Bay

Despite decades of federal and state protection, the southern sea otter (Enhydra lutris nereis) continues to experience sluggish population growth and has reclaimed only a fraction of its historic range. Managers of this threatened species have identified the growing need to facilitate range expansion via reintroductions in order to address the challenges facing southern sea otter recovery. San Francisco Bay has been identified as a candidate reintroduction site, but despite having historic presence in the Bay, sea otters have been absent from this ecosystem for over a century and it is unknown whether they could live in this highly urbanized estuary today. Sea otters attempting to resettle San Francisco Bay will contend with threats from a diverse array of human uses in the Bay, at a magnitude far greater than is currently experience anywhere else within their current geographic range. To address this knowledge gap, we used a spatially-explicit risk assessment framework to assess the quality and availability of sea otter habitat given exposure to multiple anthropogenic stressors. By incorporating risk into predictive habitat suitability modeling we are able to provide critical information to managers about the potential threats sea otters will face that could undermine their attempts to reoccupy their historic home range.