One study found 22 kinds of birds, mammals feed on salmon carcasses

By Andy Duncan When some people think about salmon they see more than a fish. They see an ecological system--a long name for a relatively simple concept. Think of it in terms of your body: The foot is connected to the ankle, the ankle to the knee, the knee to the thigh, and so on. In a way, your body is a system. If any part has problems, other parts, or your entire body, may suffer. The system salmon are part of is huge. With many species, it stretches from the mountain headwaters of streams all the way to the ocean. With some species, it stretches thousands of miles into the ocean.

Ducks move in to feed on a dead salmon in the Willamette River.

Wild salmon are hatched and live part of their lives in a watershed. A watershed is the area drained by a distinct stream or river and is separated from other watersheds by topographic boundaries such as ridgetops.

From the ecosystem perspective, the uplands and floodplain and riparian zone all affect the life in the stream. The surroundings farther down the stream affect it, too. Generally speaking, a good salmon stream has relatively cool and clean water, although the fish can adapt, within limits. Salmon need gravel to spawn. Too much sediment can disturb their spawning beds, called redds. They need a steady food supply, and structure in streams such as large woody debris and rocks for resting, hiding, feeding and rearing. Salmon are hatched in streams that are part of watersheds. A watershed is the area drained by a distinct stream or river and separated from other watersheds by topographic boundaries such as ridgetops. Uplands often make up more than 99 percent of a watershed's area, and the floodplain and stream channel make up the rest. The area immediately adjacent to the water is called the riparian zone. When they migrate to the ocean, salmon depend on an adequate flow of water to move them downstream to the estuary, where fresh and saltwater mix. Once in the estuary, they also need relatively cool, clean water and places to feed, hide and rest while they adapt to saltwater.

In fresh water and the ocean, they are part of an intricate food chain. For example, in the ocean, where many salmon species spend most of their lives, the creatures feed on tiny animals called zooplankton, and on small fish and crustaceans. These "salmon foods" need a certain range of temperatures and salinity to thrive, conditions tied to short- and long-term weather patterns.

Many people have heard of El Niño, a weather cycle that tends to bring warmer, less nutrient-rich water to the Pacific Ocean areas where Northwest salmon live. An opposite cycle, called La Niña, tends to cause upwellings of colder, more nutrient-rich water that offers better food conditions for salmon. These weather patterns affect populations of ocean creatures that eat salmon, and creatures that compete with salmon for food. Also, scientists believe there are longer-range climatic shifts in the ocean that affect salmon. These shifts play out over decades.

Salmon have other functions in this ecological system: The huge salmon runs of the past in the Northwest played an important role in transporting nutrients from the ocean to the inland environment, biologists say. When salmon die after they spawn (deposit eggs that will become the next generation), their carcasses carry important nutrients from rich ocean environments inland to the relatively nutrient-poor freshwater environment. One study determined that 22 species of forest-dwelling birds and mammals fed directly on the carcasses of spawned-out salmon.

Ecological systems are not continually stable, notes Bill Krueger, head of OSU's rangeland resources department.

"There is always change and compensation for that change," says Krueger. "You'll never have the same ecosystem tomorrow that you have today."

"In my opinion, it's very important to take the ecosystem perspective in dealing with the problems of salmon," says Bill Liss, a fisheries biologist at Oregon State University. "These days I hear people say our salmon problems are simply a result of poor ocean conditions. But what happens in the ocean and in fresh water are connected. Things that happen in fresh water can affect salmon's ability to cope with the ocean, and vice versa. It's all connected.

"An example is that, within limits, larger smolts [young salmon that migrate to the ocean] tend to have higher survival rates in the ocean," Liss continues. "High water temperatures, poor food supplies and that sort of thing in fresh water make the smolts smaller and thus poorer survivors in the ocean--probably less able to cope with ocean cycles that don't favor salmon."

Not everyone supports the systems view. But Dan Bottom, a research biologist with the Oregon Department of Fish and Wildlife, does.

"One thing that's unique about a systems view is that it requires an historic, evolutionary view that wild salmon populations have adapted to very specific conditions of a watershed in terms of rainfall, stream flow, water temperature at certain times of the year, the timing of their runs and so on," says Bottom. Also, each population may be adapted to certain ocean conditions.

"That's why when we try to put those systems back together," he asserts, "we have to consider a process that happened over millennia. We need to consider what the system was like so we know what to try and emulate."

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