Assessing the coastal occurrence of endangered killer whales using autonomous passive acoustic recorders.

Using moored autonomous acoustic recorders to detect and record the vocalizations of social odonotocetes to determine their occurrence patterns is a non-invasive tool in the study of these species in remote locations. Acoustic recorders were deployed in seven locations on the continental shelf of the U.S. west coast from Cape Flattery, WA to Pt. Reyes, CA to detect and record endangered southern resident killer whales between January and June of 2006-2011. Detection rates of these whales were greater in 2009 and 2011 than in 2006-2008, were most common in the month of March, and occurred with the greatest frequency off the Columbia River and Westport, which was likely related to the presence of their most commonly consumed prey, Chinook salmon. The observed patterns of annual and monthly killer whale occurrence may be related to run strength and run timing, respectively, for spring Chinook returning to the Columbia River, the largest run in this region at this time of year. Acoustic recorders provided a unique, long-term, dataset that will be important to inform future consideration of Critical Habitat designation for this U.S. Endangered Species Act listed species.