Natural fluctuations

By Theresa Novak Salmon are one of Nature's toughest species. Their habitat ranges between inland streams and ocean depths. They have evolved over the ages to survive many natural changes in their environment. Fossil records indicate times when salmon were plentiful and when they were scarce. Those may have been times when salmon populations were recovering from shifts in climate that brought about Ice Ages. Devastating earthquakes, volcanic eruptions, massive floods, landslides and brush fires also represented the fluctuating conditions on the landscape of salmon.

Mount St. Helens. Salmon have always had to contend with such natural changes in their world.

Given enough time, salmon have proven that they can weather such fluctuations. A recent example is that salmon are starting to return to streams through the blast zone on Mount St. Helens less than two decades after the 1980 eruption.

Salmon similarly can adapt--and sometimes even benefit--from large floods that send woody debris into streams and open up new channels that may be blocked by landslides.

But humans may be having an influence on the rate of natural fluctuations, said Dan Bottom, the monitoring coordinator of the Oregon Department of Fish and Wildlife for Oregon's salmon recovery plan.

Pollution, long-range changes in climate, shifting ocean currents that run hot and cold and pollution are suspected of having an influence on salmon.

The upsurge of cold, nutrient-rich water from the ocean depths is one natural phenomenon that benefits salmon smolts as they enter the ocean. What prompts this seasonal cold-water upwelling is not well understood. Yet when the upsurge is delayed, as it sometimes is, young salmon smolts don't get enough to eat, so more of them die.

Warmer temperatures seem to trigger another natural control on salmon-- diseases.

John Fryer, a microbiologist and retired department head of Oregon State University's microbiology program, said about 40 types of disease-causing bacteria multiply more quickly in warmer water in both streams and oceans.

While easier to document in hatcheries, the effects of warmer ocean and fresh-water temperatures are more difficult to examine, since the fish are dispersed.

One trend that appears consistent is that salmon prefer cold, wet weather rather than warm and dry, said George Taylor, Oregon's state climatologist.

A study of the weather in the Pacific Northwest and Alaska between 1896 and 1994 revealed four separate long-range climate trends. Two of them were cold and wet in the Pacific Northwest and two of these eras were mostly warm and dry.

When it was wet and cold in Alaska, it tended to be dry and warm in the Pacific Northwest, and vice versa.

Salmon populations clearly fluctuated based on the trend. Alaskan salmon reached record numbers of survival during times when it was wet and cold.

When it was comparatively warm and dry in Alaska, salmon runs in the Pacific Northwest were greatly increased.

Taylor said the past 20 years, when it was warm and dry in the Northwest, have coincided with the decline of the salmon. But he said the next 20 years appear to be starting into a wet, colder time. That could mean the natural fluctuations pendulum is swinging back in favor of the fish.

Bob Wissmar of the fisheries research department at the University of Washington in Seattle said that pendulum may be moving faster than it used to because of some human-caused factors such as pollution, possible changes to the earth's atmosphere and the increased rate of changes to the inland landscape of the salmon.

For example, some biologists observe that landslides and fires, two naturally occurring phenomena, have been increasing because of human development activities in salmon habitat.

That could be speeding up changes faster than salmon can adjust.

"We human beings think in the short term," Wissmar said. "We don't realize that the rest of the Earth operates on different time scales: decades, centuries, eons."

Where possible, he suggests that humans alter the rate of fluctuations that affect salmon to slow down changes and give salmon a chance to adapt.

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