Federal scientists probe decline of B.C. salmon runs
Federal scientists are working to solve the mystery of why Canada’s Pacific salmon is disappearing while other species, such as hake, are thriving.
In a five-year study in the Strait of Georgia, off the east coast of Vancouver Island, a team from the Department of Fisheries and Oceans is trying to determine why it has become so difficult to predict salmon runs.
According to the scientists, it used to be fairly clear how many salmon would survive and return to rivers a few years later: The prediction was based on the number of salmon that left the river. Now, scientists say the process has become far more complicated, with ocean conditions, temperature and food supply playing a much greater role in the number of salmon that return.
"We want to understand what's driving the Strait of Georgia — we're not seeing the millions of coho and chinook that drove very important recreational fisheries," said Brian Riddle, a DFO research scientist.
Salmon ecology is a complex puzzle: On the U.S. West Coast many salmon runs have completely collapsed, and in B.C. the situation is only slightly better. But in the North Pacific, including Alaska, Russia and Japan, many salmon runs are at or near all-time highs.
According to Richard Beamish, a senior scientist at DFO, the explanation for the changing stock may lie in the coastal waters where salmon spend their first few months of life.
"What we think we're seeing is food production a little earlier in the ocean, and it’s benefitting the salmon that enter the ocean first," Beamish said.
On B.C.’s southwest coast, for example, there are five main species of Pacific salmon: pink, chum, sockeye, chinook and coho. All of them eat plankton and all spend some of their first year at sea in the Georgia Strait.
The scientists are testing the theory that a one-degree increase in water temperature has effectively reduced the food supply for the salmon that arrive later in the season, such as chinook and coho.
Scientists worry the decreased food supply makes it harder for those species to fatten up and survive the first winter.
"In a very extreme way of saying it, climate change — global warming — is, in a way, starving coho," Beamish said.
The scientists are hoping their five-year study will help them understand the patterns, but they say if it is climate change that is killing Canada’s prized salmon, the question remains whether anything can be done about it.