Search

Where Do The Southern Resident Orcas Go When They Leave the Salish Sea?

This week, we travel out of the Salish Sea into the Pacific Ocean to explore some important habitat in the coastal waters off British Columbia and Washington.




Swiftsure Bank is an area of rich, productive water off the coast of Vancouver Island. It is located about 15 miles west of the entrance to the Strait of Juan de Fuca, where deep submarine canyons meet the continental shelf. As currents rise from the canyons they bring cold nutrient-rich waters to the shallow bank. This upwelling becomes the basis for plankton which in turn supports a diverse ecosystem that includes many species of fish. Many salmon migrate through Swiftsure Bank on their way to the Salish Sea, making it an important foraging area for resident orcas, and acoustic data has shown that Southern Residents are present there in all months of the year.


In 2018, Canada added Swiftsure Bank to Southern Resident orca critical habitat, which is defined as "the habitat that is necessary for the survival or recovery of a listed wildlife species.” In recent years, J, K, and L Pods have been spending more time at Swiftsure Bank during the summer months, and fewer days in their core summer habitat around the San Juan and Gulf Islands as Fraser River Chinook has continued to decline. Many people believe that these inland waters are important to the Southern Residents not just as a traditional source of prey, but for cultural reasons as well, and that their decreased presence here may have long term effects on their social structure and culture. While their absence is keenly felt, the fact that they are foraging at Swiftsure Bank during the summer, and seemingly finding abundant food is a comfort. Hopefully this prey source will continue to sustain them until we can restore the Salish Sea salmon runs to a level that will allow Southern Residents to thrive here once again.


Further south, off the coast of Washington several rivers and streams flow from the Olympic mountains to the Pacific Coast. Salmon runs in these rivers are currently relatively stable and while a number of spring Chinook runs on the west coast are in decline, they still have a good chance of recovery with robust restoration efforts. In a 2018 report by NOAA Fisheries and Washington Department of Fish and Wildlife, the Washington Coast stock was listed a priority Chinook stock for Southern Resident orcas. This stock includes Chinook salmon from the Hoh, Queets, Quillayute, and Chehalis Rivers, as well as additional small rivers that flow into Grays Harbor.


To determine priority stocks, the report looked at three evaluation factors, including: observed part of Southern Resident diet; salmon consumed during reduced body condition or diversified diet; and spatio-temporal overlap between Chinook salmon and Southern Residents. The purpose of the report was to ”identify Chinook salmon stocks that are important to Southern Resident killer whales (SRKW) to assist in prioritizing actions to increase critical prey for the whales.” Combined with additional research, this report could be an effective tool to determine where restoration and protection efforts might be most beneficial at increasing prey for the Southern Resident orcas.


Sources:

Riera, 2012. Patterns of seasonal occurrence of sympatric killer whale lineages in waters off Southern Vancouver Island and Washington State, as determined by passive acoustic monitoring

www.nps.gov.

Southern Resident Killer Whale Priority Chinook Stocks Report 2018.