| Summary: | Interactions between humans and harbor seals (Phoca vitulina) have been steadily increasing, with shoreline construction activities contributing to long-term disturbance of coastal haul-out locations. Responses of marine mammals to construction activities have been well documented, often resulting in temporary or permanent habitat displacement, aversion behavior, stress inducement, and other behavioral changes. Habituation to human disturbance is common in harbor seals - a species that spends large proportions of time hauled-out near shore. We studied a harbor seal haul-out site in Bellingham Bay located adjacent to a shoreline development project. The area surrounding the haul-out site has experienced construction activities including dredging, shoreline armoring, building removal, repaving, and drainage replacement since 2011. Construction is scheduled increase in intensity until project completion around 2025. Long-term monitoring of the haul-out site began in 2007, allowing for comparisons of seal abundances before and after construction. Seal abundances remained constant or slightly increased throughout large-scale construction activities from 2007 until September 2015 when their haul-out structure was removed. Since that removal, seal numbers have substantially decreased – particularly during the pupping season – despite the presence of nearby haul-out replacement structures. Average seal abundance during peak months before 2015 was 36.8±8.09 (n=51 counts) and after 2015 was 5.60±5.49 (n=15 counts). Seals showed evidence of habituation to construction disturbance in the presence of a stable haul-out structure and may have tolerated increased construction if the haul-out structure had remained. Our results suggest that when managing shoreline environments, maintenance of historical haul-out structures may reduce the displacement of harbor seals during construction.
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