2006. Effects of vessels on behavior of southern resident killer whales (Orcinus spp

Vessel traffic may have contributed to Southern Resident Killer Whales becoming endangered. To determine the importance of this threat, we measured behavior of Southern Residents in the presence and absence of vessels in 2003 and 2004 at two different sites along San Juan Island. Data collected include: theodolite tracks of focal individuals, along with observations of their behavior; and scan sampling of activity states of subgroups, along with counts of vessels at various distances from each subgroup. Theodolite tracks were summarized in terms of directness and deviation indices, and travel speed. Rates of respiration and display behaviors were also determined for each focal sample. Vessel number and distance were used as candidate explanatory variables for differences in track indices and other behavior, along with natural factors such as sex, age, pod membership, time of day, time of year, geographic location, etc. As with Northern Residents, directness index decreased significantly in the presence of vessels. This increase in distance traveled in the presence of vessels would result in increased energy expenditure relative to whales who can rest while waiting for affected whales to catch up. Rates of display behavior increased significantly as the distance to the nearest vessel decreased. Transitions between activity states were significantly affected by vessel traffic, indicating a reduction in time spent foraging as was observed in Northern Residents. If reduced foraging effort results in reduced prey capture, this would result in decreased energy acquisition. Each subgroup was within 400m of a vessel most of the time during daylight hours from May through September