Southern Resident orcas spend most of their time in the coastal inland waters of the Salish Sea. As a result, a NOAA Fisheries analysis showed that Chinook from the rivers that feed into Salish Sea—not the Columbia or Snake rivers which drain directly into the Pacific Ocean—are the top priority salmon stock for Southern Resident orcas. While the Columbia and Snake rivers saw a record number of adult Chinook salmon returns this past decade, Chinook populations critical for orcas did not rebound. Biologists have indicated that due to geography and timing, Snake River salmon are not the “key limiting resource or prey” for Southern Resident Orcas.

Scientists point to a loss of habitat and a population explosion of seals and sea lions in the as contributing factors to the struggles of these the salmon that orcas feed on. Researches also identified the measurable amounts of prescription and illicit drugs and other chemicals found in Salish Sea salmon populations as cause for concern.

NOAA Fisheries found that the hatchery Chinook in the Columbia and Snake river basins more than compensate for fish lost as a result of dams in terms of availability for orca whales.

NOAA Fisheries – Southern Resident Killer & West Coast Chinook Salmon
Encyclopedia of Puget Sound – Study says predators may play major role in chinook salmon declines – news
OPB, “To Save Orcas, Removing Snake River Dams May Not Be The Answer, Feds

Seattle Times, “Drugs found in Puget Sound salmon from tainted wastewater”
Defenders of Wildlife – CONNECTING THE DOTS: Orcas, Salmon, and Toxic Chemicals in the Salish Sea”
CBC, “How toxic food and toxic water could be killing the killer whales”
King 5, “Will cutting salmon out of our diets save the Puget Sound orcas?”
NOAA Northwest Fisheries Science Center – Technical Memo