The Spatial Separation of Southern Resident Killer Whales (Orcinus orca) in Relation to Boat Presence in Haro Strait, WA

It has long been suggested that the presence of boats has an impact on the behavior and biology of marine mammals.  In particular, there is a growing concern about the effects that boats might have on the Southern Resident killer whales, which occupy the coastal waters of Washington State and British Columbia.  Over the years, researchers have noted that the whales have become more spatially separated when traveling together, with pods often spread out over several miles.  To determine if vessel presence is related to this separation, we examined the Spread Out Time (SOT), that is, the number of minutes between each whale that passed our observation point, of J, K and L pods, and how this relates to the number of boats accompanying the whales.  All data were collected from shore at Lime Kiln Point Lighthouse, located on the west side of San Juan Island, WA, during the summer months from 1996 to 2006.  With all eleven years combined, a negative relationship between SOT and the number of boats present was found in J and K pods, but not L pod, suggesting that as the number of boats accompanying the whales increased, the average number of minutes between each whale decreased.  However, when examining the years individually, a significant relationship was only found in certain years (2003 and 2006 for J pod, 1997 and 2001 for K pod).  It is unclear why correlations were only found during these specific years, especially since the years differed between the two pods.  The lack of significant relationships in other years, however, suggests that the number of boats present does not influence killer whale SOT.  Other variables, such as social dynamics within pods and prey availability, should be explored to better understand why Southern Resident killer whales are more spread out now than in previous years.