New research shows some of the orca populations that visit the Salish Sea are booming while the orcas who spend most of their time there are suffering. It comes down to what the different orcas eat.
Orcas known as southern residents spend most of their time in the Salish Sea — Washington's Puget Sound, British Columbia's Georgia Strait and the Strait of Juan de Fuca separating the U.S. and Canada. Resident orcas in this inland sea only eat salmon. And, since salmon populations are declining, those orcas are starving.
Other orcas travel up and down the West Coast. They eat seals and sea lions, and their numbers have been increasing. Gary Wiles, a researcher for the Washington Department of Fish and Wildlife who wrote a report about the status of the orcas of the Salish Sea, says that's thanks to the Marine Mammal Protection Act of 1972.
“That stopped the killing of harbor seals and sea lions by fishermen,” Wiles explains. “So, because the transients feed primarily on those animals, you know, numbers have probably doubled over the last twenty-five years or so.”
At the same time, Wiles adds, the numbers don’t tell the whole story about transient orcas, which are “more contaminated than the southern residents. We have polluted waters here and those work their way up through the food chain all the way up to orcas.”
In other words, pollutants become concentrated in fish that are lower in the food chain. When seals and sea lions eat those fish, that toxic pollution becomes more concentrated in their body tissue. And so the transient orcas' prey is more toxic than that of the southern residents.
And then there’s the other kind of pollution: vessel noise. Wiles says that hurts southern resident orcas more than transient orcas because of how the residents use sonar to find fish to eat.