This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.
Declining spring usage of core habitat by endangered fish-eating killer whales reflects decreased availability of their primary prey
The salmon-eating Southern Resident Killer Whales (Orcinus orca) of the northeastern Pacific Ocean are listed as endangered both in the United States and Canada. Their critical habitat has been defined as the region of the inland waters of Washington State and British Columbia known as the Salish Sea, where they have traditionally spent much of their time from spring through fall. Using reports from experienced observers to sightings networks, we tracked the daily presence of the Southern Residents in these waters from April 1 to June 30 from 1994 through 2016. We found the escapement estimates of spring Chinook salmon (Oncorhynchus tshawytscha) on the Fraser River in British Columbia were a significant predictor of the cumulative presence/absence of the whales throughout the spring season. There was also a difference in both whale presence and salmon abundance before and after 2005, suggesting the crash in Chinook salmon numbers has fallen below threshold where it is worthwhile for the whales to spend as much time in the Salish Sea. The usage of the Salish Sea by the Southern Residents has declined in the spring months as they are either foraging for Chinook salmon elsewhere or are shifting to another prey species. In order to continue providing necessary protections to this endangered species, critical habitat designations must be re-evaluated as this population of killer whales shifts their range in response to prey availability.
PC17041 Accepted 09 April 2018
© CSIRO 2018