Climate and Capelin Explain Salmon Declines

Source: John Holyoke, Bangor Daily News

The Bangor Daily News reports that: For more than 100 years, conservationists have tried to restore stocks of Atlantic salmon in Maine rivers, including the Penobscot. Many river-specific threats to salmon, including pollution and barriers to passage in the form of dams, have been studied and demonized over the years.

Today, Maine’s rivers flow cleaner than they have in decades. Dams are being torn out, both on the Kennebec and Penobscot rivers and salmon should be flocking back. Or should they?

Earlier this month, Katherine Mills, a research scientist at the University of Maine and the Gulf of Maine Research Institute, along with peers Andrew J. Pershing, Timothy F. Sheehan and David Mountain, published a paper that paints a grim picture of the challenge facing Atlantic salmon at sea.

In that paper, Mills points out that climate change and a decline in available food — the relocation or reduction of plankton and fish called capelin — have helped lead to a decline in salmon stocks that has been taking place since 1990. And the outlook for the future is not too bright.

“What we really are seeing is that changes in salmon can be most strongly linked to the loss of capelin as a prey source for them in the Labrador Sea, but can also be tightly linked to water temperature,” Mills said.

Salmon in North American rivers take different routes on their migration paths, but eventually aggregate in a few key spots. One is the Labrador Sea, where they spend summers. Another is off west Greenland, where they spend winters. Eventually, usually after two winters at sea, Atlantic salmon swim back to the rivers where they were born or stocked.

But back in 1990, a pulse of cold water pushed their preferred bait fish — capelin — out of the area where salmon typically found them. The capelin ended up off Newfoundland instead. And they never really came back.

Kosik said Mills’ paper was eye-opening, and answered some questions that he and others have had for a long time. Among them: When the initial collapse of salmon stocks in Maine rivers began, why did some Canadian rivers fare better, at least for a time?

“Now  the Canadian rivers are starting to go down a little bit, too, so I think it’s a numbers and distribution game,” Kocik said. “How many metric tons of capelin are there, and where are they?”

Kocik said the factors that Mills uncovered seem to explain a great deal about salmon — and other species such as cod.

Kocik and Mills both admitted that much of the salmon conservation work and study that has taken place has focused on the rivers; less has focused on ocean survival of the species. And below that, there are knowledge gaps that need to be filled, Kocik said.

“People study plankton. People study salmon and tuna. There’s not a lot of work done on capelin that are the middle of the ecosystem and make everything click; hAabitat improvement and capelin research are among the areas that can make a difference” Kocik said.

To read the full feature click HERE

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