HELENA, Mont. — It seemed like a good idea at the time: Plant freshwater shrimp as a new food source for popular landlocked kokanee salmon. But the salmon are gone from Flathead Lake now; the shrimp project disrupted the lake's food chain in ways unimagined.
The opossum shrimp project of the 1960s and '70s, repeated at more than 100 lakes in the western United States and Canada, showed how messing with fisheries can go wrong. Nationwide, millions of dollars are being spent on attempts to undo the introduction of aquatic species and reestablish those of earlier times.
Biologists say they cannot fully reverse the work of government agencies and "bucket biologists"--people who drop alien fish here and there--but they hope to renovate some fisheries to help native species. Of the 30 extinct fish species in the United States, nonnative species were involved in the extinction of 24, according to the U.S. Geological Survey.
"Once you introduce something, there's virtually no going back," said Don Baltz, a Louisiana State University professor who heads the Introduced Fish Section of the American Fisheries Society.
Still, across the country, there is an array of projects: the planned return of arctic grayling to the Missouri River headwaters; efforts against predacious northern pike where vulnerable species are in steep decline; and removal of fish to make way for various species of trout, including the westslope cutthroat described in the journals of explorers Meriwether Lewis and William Clark.
Signs of success include the greenback cutthroat trout restoration at Rocky Mountain National Park in Colorado.
The USGS reports nearly every state saw dozens of alien species placed in inland waters between 1850 and 1998, sometimes involving intrastate movement of fish from one lake to another. California leads with 147 introduced species, followed by Florida with 120, Colorado with 107 and Texas with 105. Alaska trails, with just nine.
At Montana's Flathead Lake, the largest natural freshwater lake in the western United States, the kokanee swept out by the shrimp were themselves introduced, in 1916, and eventually replaced native west-slope cutthroat as the major sport fish.
The opossum shrimp, found in the Great Lakes and elsewhere in the East, were introduced to nearby Whitefish and Swan lakes, where they were planted to boost the kokanee. But the project backfired; in Flathead Lake, as elsewhere, the crayfish-like shrimp competed with kokanee for food and became part of the diet for lake trout, which then preyed on the kokanee.
"It was one of the greatest mistakes in fishery science," said Jack Stanford, director of the University of Montana's Flathead Lake Biological Station. "This shrimp, this little shrimp, changed Flathead Lake forever."
To fishermen like Walter Bahr of Kalispell, the effects of tinkering with nature are obvious.
"Early on when I started fishing, it was almost strictly cutthroat and bull trout, and some of the native whitefish," said Bahr, who has fished Flathead Lake for 60 years. "Then we saw the kokanee salmon, and that was an excellent fishery for several decades." Now Bahr catches primarily lake trout, and he returns most to the water.
"There used to be several hundred boats on a nice day," he said. "Now it's 30 to 50."
The popular, 185-square-mile lake is renowned for its clarity. Zooplankton consume the algae, but the shrimp voraciously eat the zooplankton, tiny aquatic animals also consumed by immature kokanee.
The cascading effect of the shrimp also touches the bull trout, listed as a threatened species last year. Scientists believe lake trout, which feed on the shrimp, compete with bull trout for food and space, and prey on young bull trout.
The effects were dramatic even in Glacier National Park, more than 40 miles upstream from Flathead Lake. Until the 1980s, migrating bald eagles would pause by the hundreds each fall to feast on spawning salmon. A half-dozen bald eagles might perch in a single tree overlooking McDonald Creek, swooping down occasionally to grab salmon in their talons.
Special crowd restrictions were instituted for tourists each fall. Now the salmon no longer come. Neither do the eagles. Neither do the tourists.
Any measures to eliminate the shrimp would kill too much other lake life, said Jim Vashro, a Montana Department of Fish, Wildlife and Parks manager in Kalispell. Vashro said management of Flathead Lake now focuses on working around the shrimp, not eliminating them.
Stanford's studies found shrimp counts in the lake up 50% in the last couple of years.
Variety was the goal in the early fish introductions decades ago, as people migrated to the West.
"I think it was a matter of people wanting the fish they grew up with," Stanford said. Some took it upon themselves to plant fish; others left the task to the U.S. Fish Commission, forerunner of today's U.S. Fish and Wildlife Service.