May 23, 2002

By Jeff Brady

PORTLAND, OR (Oregon Considered) - Before rivers were dredged and dams were built—even before there was commercial fishing and logging—salmon populations varied widely. An article published in the scientific journal 'Nature' last month reached that conclusion by studying layers of sediment from the bottom of an Alaska lake.

Salmon lay their eggs in inland waterways. The baby fish travel to the ocean where they spend a couple of years. The few who survive return to their birthplace and lay more eggs, starting the process all over again.

When salmon come back from the ocean they bring with them unique nutrients that aren't found inland. When they die, those nutrients remain behind. Researcher Bruce Finney at the University of Alaska at Fairbanks studied sediment layers from a lake on Kodiak Island.

By measuring the level of these unique nutrients, he was able to determine the level of salmon runs over the past 2,200 years. Finney's analysis shows that runs were at historic highs about 2,200 years ago.

Finney: And then right around 2,000 years ago there's a significant crash and the populations go to the lowest levels seen in the 2,000 year history. And then they stay low for several hundred years and then they start to climb up to higher levels at about 1,200 years ago. And by 800 years ago they're near the highest levels of the whole record again. And there's some variability but those high levels are sustained almost for 800 years until about the turn of the century—to the early 1900s.

Finney says the numbers have been declining ever since. He says that first big decline appears to be associated with a significant climate change, but he says the temperature itself is not the main factor. Finney says the temperature affects conditions in the ocean.

Finney: The idea is that it's the food that the salmon are able to eat when they're in the ocean that's the most important thing and that's controlled by the climate change.

Finney says during the natural lows, hundreds of years ago, some fish almost became extinct. The conclusion: ocean conditions have a huge effect on salmon populations inland. But Finney says that doesn't mean humans don't also have an impact on fish.

Finney: The message, in terms of salmon restoration, is that we need to recognize that climate change does have these big impacts. And so when there's periods of bad climate, those are periods where man has to do everything in their power to make sure salmon don't have other strikes against them. So that's the time when it's very important not to over fish… Very import to have the habitat in good shape because if they have three strikes against them then those are the kind of situations that have led to extinction and so forth.

Right now, fisheries experts say salmon runs in the Pacific Northwest are on the rise. Again ocean conditions get the credit. But Finney says that doesn't mean humans can relax restoration efforts.

Finney: And on the other hand when you're entering a good climate state I don't think it also means that this is time to relax and fish 'em harder because that's the time—those are the opportunities—where stocks can be rebuilt.

Finney says that rebuilding is necessary to get through the next period when ocean conditions are bad again. Finney's research has contributed to the understanding of how salmon populations vary over a long period. Bill Peterson, an oceanographer with the National Marine Fisheries Service, says that's valuable. He says it's also important to understand there are short-term cycles. For example, he says, coho runs started declining in the late 70s. In 1999, after the most recent El Nino, runs started coming back. That can provide a motivational boost for people working to restore fish habitat.

But Peterson says the main message is that habitat restoration and good ocean conditions work in combination to restore fish runs.

Peterson: Say you're in charge of some small stream and you're restoring the habitat, you've got gravel and everything you can possible do and nothing seems to be working… Well, you should be patient! And when the cycles turn around, like they have the last couple of years, things are gonna come back and look great!

University of Alaska researcher Bruce Finney says the next step for scientists is to figure out how to predict the climate variations that change ocean conditions. That would give scientists the information necessary to avoid extinction of a species during the low part of a salmon cycle.

© Copyright 2002, OPB (Oregon Public Broadcasting)

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