HAUL-OUT SELECTION BY PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII): ISOLATION AND PERCEIVED PREDATION RISK

The potential for non‐aquatic predators to influence habitat use by harbor seals (Phoca vitulina) in a nearshore marine environment was studied by examining haul‐out site use and through an experimental approach. Distance from shore, distance to possible foraging depths, peripheral water depth, and haul‐out areas were quantified for each haul‐out. There was a positive relationship between the number of seals hauled out and the distance from shore for eight known haul‐out sites. The hypothesis that harbor seals increasingly hauled out farther offshore to reduce predation risk was tested experimentally by measuring their response to a model of a potential terrestrial predator in comparison to a control object, and to disturbance by a human at one of the study sites. Harbor seals abandoned the haul‐out in the presence of the predator model, but showed little response to the controls, suggesting they possess a threat image for terrestrial predators and avoid hauling out when it is perceived. These results support the hypothesis that harbor seals select isolated sites to reduce exposure to terrestrial carnivores.