Could a seal cull in Canada help Salish salmon and Southern Resident orcas?
One of the biggest issues facing Puget Sound’s endangered Southern Resident killer whales is a lack of Chinook salmon, their preferred food. A Seattle chef and the PCC Community Markets chain have stopped selling local Chinook, in an effort to help provide more for the orcas.
The mystery is what happens to them in their first year of life as they head out to sea, before humans would catch them. Some scientists think booming numbers of harbor seals are to blame – and that culling them could quickly make a difference.
Canada’s Department of Fisheries and Oceans is considering a proposal to allow the killing of up to half of British Columbia’s harbor seals, through a commercial hunt.
A group called the Pacific Balance Pinnepeds Society submitted a 55-page document on the idea last October. It has the support of some First Nations groups who want to take part in the hunt.
Carl Walters helped write the proposal. He’s a retired professor of fisheries at the University of British Columbia who has been researching salmon scarcity for 50 years.
“So it’s their survival rate from the time they get to sea until they’re big enough to get caught that has collapsed,” Walters said.
The decline has put the numbers of those fish at about 80 percent of where they were 50 years ago, he says. He started studying the problem in the 1970s and says he’s looked into all kinds of causes.
He’s ruled out over-fishing by humans because, he says, commercial fishing today has been dramatically reduced over the past several decades, with no improvement in the number of fish coming back. He’s also studied and ruled out the influence of hatcheries and even rising water temperatures, which can be deadly for young salmon, especially in shallow rivers. He says he’s left with a key culprit that he says his data confirms.
“What we’ve found is that the decline and survival is very well correlated with increases in seal populations in the Georgia Strait," Walters said. "They’ve gone up by tenfold over the last 30 years.”
He says a targeted hunt to reduce the harbor seals' numbers could bring the ecosystem back into balance and potentially provide more Chinook salmon in just a few years – both for commercial fisheries and for Southern Resident orcas.
Canada’s DFO says it is reviewing the proposal, but there is concern about transient killer whales, for whom seals and sea lions are an important source of food. Those orcas are listed as threatened under Canadian law.
Meanwhile, Washington's Department of Fish and Wildlife is taking a comprehensive look at the impact of seals and sea lions on Chinook salmon.
Nate Pamplin with the Washington Department of Fish and Wildlife says authorities here are still gathering information, especially in Puget Sound.
“We’re still wanting to compile that data – of harbor seals in particular – to determine first off: what is that level of predation? And then secondly, looking at the different options under the Marine Mammal Protection Act for what can be done about it,” Pamplin said.
One option might be blocking areas where the seals tend to gather near estuaries with lots of vulnerable tiny fish, which can get caught by hungry seals that tend scoop up everything while they’re hauling out, but do not seek out the fish as a preferred prey the way the Southern Resident killer whales do once the fish have matured at sea.
Pamplin says prior to culling any seals, the state must complete a thorough scientific evaluation that’s underway. And there would need to be convincing, peer-reviewed evidence that the killing would have the intended consequence of reducing juvenile salmon mortality.
He says WDFW expects to have results in about a year to present to Gov. Jay Inslee’s orca task force and other interested parties.