The Effects of Disturbances on Harbor Seals (Phoca vitulina) on a Haul- Out site Off Yellow Island, Washington

Abstract

Human induced disturbances affect harbor seals (Phoca vitulina) hauled-out off Yellow Island, WA. Disturbances, in this study, include sailboats, motorboats, wake height, and distance of boats to haul-out sites (0 to 200 m). Harbor seals are protected under the Marine Mammal Protection Act (MMPA) and regulations set by the National Marine Fisheries Services (NMFS), state that no vessels should approach closer than about 100 m to marine mammals. During our study, we observed 41/71 boats that passed within 100 m of the harbor seals on their haul-out site. We recorded disturbance behavior of harbor seals as vigilance and flushing and recorded their location on the haul-out site as low, waterline to 1 m, and high as any seals above 1 m. Our results indicate that in general, seals below 1 m are more vigilant. During wake disturbances, we recorded a mean vigilance of about 40.2% as compared to those about 1 m up on the haul-out site with a mean vigilance of 8.6% . Again, seals were more vigilant in low areas when comparing distances of boats to vigilance. Out of all the disturbances (i.e. sailboats, motor boats, and wakes), wakes causes the highest amount of vigilance. Our results indicate that regulations set by the NMFS and MMPA need to be revised; specifically the 100 m distance that vessels are required to avoid approaching marine mammals.