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Responses of Pinnipeds to Navy Missile Launches at San Nicolas Island, California
Abstract: To document the responses of pinnipeds to launches of missiles and similar aerial vehicles, three species of pinnipeds were observed during 77 launches from Navy-owned San Nicolas Island off California from August 2001 to October 2008. Pinniped behavior and flight sounds during each launch were recorded by unattended video cameras and acoustic recorders set up around the island’s periphery, usually in pairs, as vehicles flew over or near haul-out sites. Multiple logistic regression was used to assess dependence of pinniped responses on received sound, distance from flight path, type of vehicle, and natural factors. The majority of observed California sea lions (Zalophus californianus) startled and showed increased vigilance up to 2 min after each launch; responses often included movement on the beach or into the water and were significantly related to received sound level and distance from the vehicle’s closest point of approach. Most observed northern elephant seals (Mirounga angustirostris) showed little reaction to launches and merely raised their heads briefly. Nonetheless, their responses were also related to received sound level and distance from vehicle trajectory. The harbor seal (Phoca vitulina) was the most responsive species. During the majority of launches, most (average 68%; range 7 to 100%) observed harbor seals within ~4 km of the launch trajectory left their haul-out site by entering the water; harbor seals hauled out again at the same site several hours after a launch. Within the range of conditions studied, there was no clear correlation between harbor seal response and received sound level or distance from the closest point of approach of the vehicle. Despite these short-term behavioral reactions, the effects of launch operations are likely to have been minor and localized, with no consequences for local pinniped populations as pinniped population sizes on San Nicolas Island are stable or increasing.
Key Words: disturbance, launch sounds, missiles, California sea lion, Zalophus californianus, northern elephant seal, Mirounga angustirostris, harbor seal, Phoca vitulina
Document Type: Research article
Page Numbers: 139-150