Orcas feasting on seals -- which helps salmon
- Scientists estimate that transient orcas in Hood Canal have eaten more than a third of the 1,500 harbor seals believed to have been living in the waterway when the whales arrived seven weeks ago. That means fewer seals will be feasting on summer chum and chinook salmon, which could turn out to aid the recovery of the threatened fish.
"They've made a significant predation impact on the harbor seal population in Hood Canal, no matter how you look at it," said Steve Jeffries, a marine mammal biologist with the Washington Department of Fish and Wildlife. "The take-home message is that the transient killer whale population is bad for the seal population but good for the salmon population, because seals eat salmon."
For anyone worried about the seals, Jeffries added, "The harbor seal population may have suffered, but we expect they will recover over time."
It's actually unusual for the transients to venture this far inside the Sound (the Hood Canal, incidentally, is not manmade by any means; it's just a long narrow finger of the Sound). But it brings up an important point.
Humans have been playing God with this ecosystem for a long time. For awhile, orcas were captured from these waters (this is where the killer-whale display industry originated, in fact), and fishermen used to shoot at them with impunity, believing them to be competitors for their salmon. Orcas are of course very smart and have long memories, and thus few of them ever venture far into the Sound anymore, which is where many of the old captures took place. This includes the transients, who are the only orcas that eat seals and sea lions (the resident orcas are exclusively fish eaters).
The result has been an unfortunate overpopulation of seals and sea lions (or pinnipeds), particularly at the mouths of streams where salmon runs are bottlenecked. For awhile in Seattle, fish and wildlife officials have been forced to resort to a relocation and intimidation program to keep sea lions from venturing up to the locks in my neighborhood and munching on salmon.
More than a few biologists have been concerned about the additional effect of pinniped predation on salmon runs. However, they are under the purview of the Marine Mammal Protection Act and there is little that can be done by humans to limit their population, short of hunting them again.
Seems that Mother Nature has a suggestion of her own.