Predicting Oil Spill Impacts on Southern Sea Otters (Enhydra Lutris Nereis): Application of a Mechanistic Movement Model

Oil spills that unpredictably overlap with sea otter habitat are the most serious threat to 2,941 sea otters off coastal California. Multi-year radio telemetry data indicated that movements of individual sea otters generally were concentrated within areas of common use or focal centers within their home range, similar to terrestrial mammal den sites. Sea otters could encounter oil when moving within their focal centers inside the area of an oil spill or by traveling into the spill when transiting between focal centers. We better predicted the dynamic nature of sea otter-oil interactions than previous studies by quantifying the intersection of 1) 5-day simulations of sea otter population movements using a multi-state biased correlated random walk (BCRW) model with core dynamics driven by an Ornstein-Uhlenbeck process, and 2) 5-day trajectories of six hypothetical oil spill scenarios of a short-term, large volume oil spill. The sea otter-oil spill interaction model predicted that an oil spill off the central California coast during winter with average southeast prevailing winds would expose the greatest numbers of sea otters to spilled oil (810 individuals or 33% of the total simulated population) than a spill during spring or summer collectively (558 or 23%). Our integrative model can assist managers developing oil spill response plans and provides an example of how movement data can be used to quantify potential risks impacting nearshore ecological resources