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.