With increased human populations and tourism in coastal areas, there is greater potential for disturbance of marine wildlife. Having high metabolic rates, sea otters (Enhydra lutris nereis) are at risk of increased energetic costs due to disturbance. To investigate these effects, sea otter activity in response to potential disturbance stimuli was recorded over three years, at three California locations: Monterey, Moss Landing, and Morro Bay. A hidden Markov Model was developed to examine how activity varies as a function of location, group size, pup to adult ratio, kelp canopy, and occurrence of and proximity to disturbance stimuli. Results were combined with published estimates of activity-specific metabolic rates, translating activity change into energetic costs. The effects of disturbance stimuli on sea otter behavior appear location specific, and vary non-linearly with distance from disturbance stimuli. The model quantifies the distance-disturbance relationship, calculating distance at which the likelihood of disturbance is low (i.e. averaged across locations, there is \u3c10% potential for disturbance when stimuli are \u3e54 m away). Energetic costs (kJ) for Monterey, Moss Landing, and Morro Bay (given six small-craft approaches of 20 m for a 27.7 kg male otter in kelp, group size 10, and pup ratio 0.5) are expected to increase by 210.1 kJ ± 80.76, 160.07 kJ ± 65.24 and 58.44 kJ ± 23.66, respectively. Our analyses represent a novel approach for estimating behavioral responses and energetic costs of disturbance, furthering understanding of how human activities impact sea otters and providing a sound scientific basis for management
