From the desk of Joseph Bogaard
February 2, 2014
A recently-published study from the Journal of the Acoustical Society of America makes new findings that connect endangered Southern Resident Killer Whales (SRKWs) with threatened and endangered salmon of the Columbia and Snake Rivers. NOAA-Fisheries, the federal agency charged with protecting has previously identified the historic predation by these orcas on Columbia Basin chinook salmon and have previously described the decline of salmon in the Columbia River basin as “[p]erhaps the single greatest change in food availability for resident killer whales since the late 1800s...”
Today, there is strong evidence that the SRKWs are often suffering from severe nutritional stress (starving). The lack of available prey has been documented as a key source of mortality and low reproductive success in recent years. This new study confirms the recent presence of SRKWs at or near the mouth of the Columbia River in March/April and speculates that they are drawn there to feed on oily, energy-rich spring chinook that also gather at the river’s mouth in March before beginning their upriver migration.
Needless to say, a Columbia Basin that produces many more chinook salmon would be a very good thing for SRKWs and help address what scientist consider orca’s biggest threat: lack of a sufficient prey base to support their survival and recovery.
The study’s abstract below nicely summarizes the study’s findings, followed by a link to the full study.
Assessing the coastal occurrence of endangered killer whales using autonomous passive acoustic recorders.
By M. Bradley Hanson, Candice K. Emmons, and Eric J. Ward
Journal of the Acoustical Society of America, November 2013.
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.
You can read the full study here.