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Public Radio's Environmental News Magazine (follow us on Google News)

Salmon and Climate Change

Air Date: Week of

A new study links the decline of salmon in the North Pacific ocean with global climate changes impacting marine ecosystems. Host Steve Curwood talks with Dr. David Welch, from the Canadian National Department of Fisheries and Oceans, about the study and its implications for the future of salmon.


CURWOOD: For years, marine scientists have been stumped by the rapid decline of salmon populations in the north Pacific Ocean. The numbers are going down too fast to simply blame over-fishing, dammed rivers, and pollution. Now, a new study sponsored by the World Wildlife Fund, suggests global warming may be a factor. Climate change effects on ocean ecosystems are largely unknown, according to David Welch, head of the High Seas Salmon Research Program for the Canadian Department of Fisheries and Oceans, and one of the scientists involved in the study. But, he says, evidence is starting to mount that the North Pacific Ocean is no longer a friendly place to the salmon.

WELCH: What is happening is we're seeing a physical change in the structure of the ocean. It's warmer at the top. It's got more fresh water from runoff from rain or from glacier melt water. Both of those things seem to be sealing off the surface layer from the deep ocean. And that's the area where we have most of the nutrients. There's no light, so the plants can't grow there. The ocean, through storms and other processes, has to bring that nutrient to the surface, where the plants can then use it. They produce food that then goes up the food chain, and eventually turns into what the salmon eat.

CURWOOD: What exactly kills the salmon?

WELCH: What seems to be happening is that they're growing more slowly. Small fish have higher mortality rates, because there's more things around to eat them. So when growth is cut back, they stay small for a longer period of time. As a result, they have higher mortality and fewer fish come back from the sea. Salmon survival, compared to 2 decades ago, for some species, is only one tenth of what it was. We've always thought of the ocean as being a very stable place for salmon. We now know that's not true.

CURWOOD: Salmon have been in trouble for a long time. We've put up dams where they go to spawn. We've contaminated the water where they go to spawn. There's also been development in those riparian areas where they go to spawn. And of course they're been heavily fished. What proportion of the problem that salmon are having there in the Pacific Northwest would you attribute to climate change versus all those things that have happened in the freshwater riverways for them?

WELCH: All of these things are very interlinked, so it's difficult to tease out one versus the other and point a finger and say this is causing almost all of the problems. What we do know is that there have been large-scale changes in the climate, that are affecting survival in both the ocean and in fresh water. But what we are seeing now in the 80s and the 90s is that the changes for the worst in the ocean are actually larger than the changes in fresh water survival. That's a big surprise even to scientists, because we usually think of the ocean as being so big and so wet that it can't possibly have changed that fast for an animal like salmon. Let me put it in perspective for you, Steve. In the 1980s, for every 5 adult salmon that would come back from the ocean that could be caught, we might now only catch 1. So only 20% survival or 25% survival, perhaps, is now typical compared to what was happening in the 80s. Now, some component of that is probably global warming. My personal bet is that we're going to establish over the next 10 to 15 years that a very large component of these changes are due to global warming.

CURWOOD: What impact does the loss of salmon have on the Pacific Ocean system as a whole?

WELCH: Well, the reductions in salmon populations affect us all. It affects both the ecosystem, and it also affects humans. It affects the ecosystem because salmon are one of the key predators. If you wanted to go out anywhere in the North Pacific Ocean, and dip in that, 95% of the fish that you'd catch that were over the length of your finger would be salmon. That's a big component of the ecosystem out there. For all of us living along the shores of the North Pacific, whether in Asia or in North America, salmon in northern areas is a very important part of our economy. It's also an obligation that we have to maintain a part of the ecosystem.

CURWOOD: In the course of doing this research, you looked at a number of factors beyond salmon. What's the message here? What does this research on changing temperatures and the oceans tell us?

WELCH: The message is, I think, that we're moving into terra incognito. On the old charts from the Middle Ages, cartographers, when they drew their maps of the oceans, wrote, "Here be dragons," things they didn't understand. We're going to be facing more and more of them. The climate system, we don't understand enough about it as scientists to be able to tell people precisely how the climate is going to change and what the consequences are going to be. But people rely on stability. Ecosystems rely on stability. And that's going to be the thing that we're going to have the least of. We're going to be moving into a period of very rapid change, and as scientists we're going to be stressed ourselves, and very hard-pressed, to try to find answers to these questions. But as a person, I don't want to simply be documenting what's happening, and saying this is what happened. We need to be able to be proactive, realize these things are going to happen, and that science is not going to provide us with all of the answers as to what's happening. There is a serious public debate that needs to be engaged in on where we're going to go in the future and how we go there.

CURWOOD: Dr. David Welch, head of the High Seas Salmon Research Program for the Canadian National Department of Fisheries and Oceans. Thanks for joining us.

WELCH: Thank you, Steve.



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