Adding to the Circle of Life
On a typically gray, gloomy day last November in Oregon, the skies opened over the Mt. Hood National Forest and it began to rain fish.
Over two days, about 70,000 pounds of coho salmon fell, courtesy of a bucket-like device dangling beneath a large helicopter. Upon impact--the splashes could be heard from half a mile away--most of the fish went belly up and lodged behind rocks and downed logs. Others were swept away in the current, to become a meal for wildlife residing near branches of the Clackamas or Sandy rivers, the targets of this strange exercise in salmon restoration.
The thousands of fish that fell those two days were dead long before the Oregon Department of Fish and Wildlife and the U.S. Forest Service deposited them into the rivers. The agencies had initiated the carcass drop--using excess fish taken from hatcheries--because of a growing body of scientific evidence showing that dead salmon are precisely what’s missing from many river ecosystems in the Pacific Northwest.
The thinking goes like this: Before Europeans settled the region, tens of millions of salmon migrated from the ocean each year to spawn and then die in the same rivers where they were born. Some of the fish were caught by the region’s Native Americans, but millions simply perished in the rivers, where the decaying bodies turned into a feast for insects, eagles and, perhaps surprisingly, young salmon.
To put it in more human terms, the final gift that adult salmon gave their kids was an easy meal.
Today, human activities--including dam building, logging and hatcheries that dilute the genetics of wild stocks--have greatly reduced salmon numbers, and many of the historic runs are endangered. What scientists now want to know is how the removal of that once-abundant food source has altered river ecosystems.
One of the first researchers to focus on the role of dead salmon in river ecosystems was Mark Wipfli, who went to Alaska in 1992, fresh out of graduate school, to be an ecologist with the forest service.
“When I first arrived in Alaska, I noticed the streams didn’t seem to have a lot of aquatic insects, but they produced so many young salmon,” says Wipfli. “There were a lot of salmon coming out of these systems, but not a lot of food. Both myself and some others began thinking there was something going on in those streams that wasn’t obvious.”
Wipfli and his colleagues soon began canvassing streams, and found that waters with salmon carcasses usually had more insects, higher levels of nutrients and young salmon that grew faster and bigger than in streams without salmon runs. About the same time, other researchers in the U.S. and Canada were reaching similar conclusions: Decomposing salmon appeared to be the foundation for the region’s aquatic ecosystems.
One researcher found at least 138 wildlife species that had some type of relationship with salmon, including 32 mammals and 38 birds. Bald eagles, bears, raccoons, minks, otters--to name just a few--fed directly on the carcasses. Many other creatures seemed to enjoy indirect benefits. A small bird called the American dipper, for example, profited from the increased population of insects.
Dead salmon aren’t so much at the bottom of the food chain as at the center of a complex food web that extends from river bottoms to forests far from the water’s edge, researchers are learning. Birds, mammals and insects pass nutrients into the soil, benefiting streamside vegetation. Such plants, in turn, help salmon by providing shade and dropping leaves and needles into rivers, providing even more food for insects.
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Fully Understanding the Impact Could Take Years
But fully understanding the many impacts that salmon have on ecosystems will take years, perhaps decades, researchers say. One way to test the effect of carcasses is to reintroduce live salmon into a river where they once spawned but are now absent. That could occur in a few years in Washington’s Olympic National Park. The Elwha River spills from the park’s high country into western Puget Sound. But two dams on the river, one built in 1912 and the other in 1927, block migrating salmon from reaching the upper 67 miles of the Elwha.
Before the dams were built, all five species of salmon native to the Pacific Northwest inhabited the river, including chinooks that occasionally reached 100 pounds. If funding from Congress comes through, the dams could be removed by 2005, which may enable nearly 400,000 salmon to one day return to the river.
“We call the Upper Elwha largely pristine because the habitat is still intact,” says Brian Winter, head of the Elwha restoration project for the park service. “But the fish aren’t there, and all the nutrients that were historically there and taken up by riparian vegetation and wildlife aren’t there. For visitors to the park’s back country, the Elwha might look pristine. But it isn’t.”
That may change if the dams come down. Some of those fish will be harvested by tribes and anglers. But most, says Winter, will be allowed to do what salmon have done for thousands of years--spawn, die and become a meal for other wildlife.
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Restocking and Monitoring the Results
Until that happens, the best way to determine the salmon’s role in ecosystems is to restock the carcasses that human activities have removed from rivers and then stand back and monitor the results.
“This is not a one-time thing,” says Dan Shively, a fisheries biologist for Mt. Hood National Forest. “We plan to keep doing this as long as fish keep coming back from the ocean. And a program like this was received very favorably by the public, as long as we paid attention to some water-quality issues and avoided dropping salmon in people’s backyards.”
