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Scott Terrell

* Climate change already affecting Northwest forests and fish runs

Survival for salmon is a numbers game: Lay enough eggs, and some will make it to adulthood to breed.

Each female chinook salmon lays 4,000 to 6,000 eggs and then dies.

Of the millions of eggs laid in the rivers feeding the Puget Sound, about 1 million wild chinook will survive to swim to the Pacific Ocean, said Pat Pattillo, state Department of Fish and Wildlife salmon policy coordinator.

After a couple of years at sea — provided the chinook avoid predators and fishermen in Alaska — 40,000 might return to Puget Sound rivers to spawn in a good year, he said. The Skagit River was expected to see 15,000 chinook return this year.

But returns for the Sound are more commonly between 20,000 to 30,000 for chinook, about a 1 percent survival rate, Pattillo said.

Not the kind of odds you’d want to bet the house on — especially in a bad year.

And scientists say that climate change could create conditions that will make it tougher for the Sound’s five species of salmon and for the steelhead trout, which was recently listed as threatened under the Endangered Species Act.

Scientists using computer models to predict the impact of rising sea levels, warming oceans and rivers, and low stream flows on salmon say that it’s possible the spawning populations in some watersheds could drop by 50 percent by 2050.

No one is saying that the effects of a warmer Earth will force salmon species, such as the threatened chinook, into extinction. But scientists don’t know how quickly the coldwater-loving salmon can adapt to the rapidly changing conditions.

“Little is known about the capacity of salmon to adjust to climate change,” according to a study published by National Academy of Sciences on the impact of climate change on chinook in the Snohomish River basin.

Salmon are part of the complex ecological systems of both the Puget Sound watershed and the Pacific Ocean. A state wildlife report found that 137 animal species — from ducks that dine on their eggs to orcas and seals that gulp the returning adults to bald eagles and insects that eat the spawned-out corpses — depend on salmon either directly or indirectly for food.


Salmon habitat affected

Several recent studies using computer models indicate that climate change will affect salmon in several ways:

* Rising seas could reduce habitat size for young salmon, which may spend several weeks in the estuary preparing for the change from fresh water to saltwater.

* Lower summer stream flows could mean that juvenile salmon, especially coho, will have less habitat and food during the one to two years they spend in the river.

* Increased incidents of flooding will wash away more salmon eggs from streambeds.

* Warmer stream temperatures can cause the fish what amounts to heat exhaustion.

* Higher stream temperatures reduce the amount of dissolved oxygen, making it difficult for salmon to breathe.

* Warmer oceans, such as in an El Niño year, bring other species, such as squid, north where they compete with adult salmon for food.

* Warmer seas prevent the upwelling of the nutrient-rich cold water, reducing the amount of plankton and bait fish, which are an important part of the food web that salmon need.

Scientists studying both salmon and climate change qualify their research by saying the environment is a complex system, which has led them to make a number of assumptions in their computer models.

Although those models can help predict possible impacts of climate change, researchers caution that they cannot account for all variables. For instance, a model looking at sea level rise can indicate where dry farmland might become salt marsh. But it cannot predict the impact of decades of fertilizer and pesticide on the animals and plants that might live in the newly created marsh.

“There’s a lot of uncertainty,” said Greg Hood, a senior restoration ecologist at the Skagit River System Cooperative.

In 2005, Hood published a study using a computer model to look at the possible impacts of sea level rise on salmon habitat on Fir Island in the Skagit River delta. His model predicted that an 18-inch rise in sea level — slightly above the middle of the range of the scenarios predicted by a team of Nobel-prize-winning scientists for 2090 — would lead to a 12 percent loss of salmon habitat. A 32-inch rise would result in a 22 percent loss of habitat, he said.

Hood said he assumed that the remaining marsh habitat would allow salmon to thrive and assumed a 12 percent and 22 percent decline of juvenile chinook — 211,000 and 530,000 fish respectively.

He and two other researchers are working on a more complicated model of the effects that sea levels will have on fish habitat in the delta. That model, which will take another 21⁄2 years to complete, may help make choices about where habitat should be restored.


Stream flows could change

The loss of salmon could be much higher than what Hood predicted in 2005 because his model assumes that the lost habitat is just as productive as what remains.

“The complicated answer is we don’t know,” Hood said. “What climate change is going to focus us on is it’s going to force us to deal with uncertainty.”

If a rising sea weren’t enough for salmon to contend with, climate change could force the fish to deal with other water issues, such as too much water flow and too little.

The increases in flooding predicted by the University of Washington’s Climate Impacts Group likely will scour eggs from the gravel streambeds where they are laid, said Jeff Haymes, state wildlife coho salmon fisheries manager. The eggs would be lost, and the fish won’t hatch.

Reduced snowpacks mean lower stream flows in the summer, causing at least two problems.

For coho, as well as steelhead trout, which spend one or two years in the rivers that spawned them, less water will cause “population bottlenecks,” Haymes said. With more fish sharing less space, the competition for resources will put stress on the fish, he said.

Chinook salmon that depend on high-elevation drainages could experience a 50 percent decline in their numbers by 2050, according to a study published by the National Academy of Sciences.

That study looked at water temperature, oxygen levels and stream flows in the Snohomish River Basin under two climate scenarios.

Without habitat restoration, the population of spawning chinook in the river basin could decline by 20 percent to 40 percent by 2050, according to the study.

Habitat restoration can limit the decline to 5 percent in one scenario and in the other, the salmon population begins to bounce back with a 19 percent increase, according to the academy study.

It remains to be seen whether the cold water fish, which prefer temperatures below the 60s, can adapt to a warmer Earth, Haymes said. Salmon evolved in the past 10,000 years to survive catastrophic events, such as landslides cutting off their spawning streams, Haymes said.

“Salmon are highly adaptable normally — quite plastic in the conditions they can adapt to,” said Haymes, adding that salmon also need certain habitat conditions at certain times of the year. “Global warming will change those conditions.”

But the warming is not the only thing salmon are facing. They’re also coping with toxins in the water, changes in stream runoff and contaminants caused by development, Haymes said.

“You layer on the insults of human activity, and you have a double whammy,” he said.

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Skagit Warming: Tell us what you think

* Marta Murvosh can be reached at 360-416-2149 or .