Fish swap planned as part of scenic lake's rehab

Readers of a certain age may remember the story of an American general speaking of the need to destroy a Vietnamese village "in order to save it."

Similarly, perhaps, scientists out in Banff National Park in Alberta are planning to purge Moraine Lake of exotic fish and then replenish it with native trout.

It's not quite as crazy as it may sound: Park officials are looking to clear out brook, lake, and rainbow trout, and other "introduced" species, in order to provide a more congenial habitat for the bull trout, a native species that over recent decades has been increasingly crowded out of its own home. Today, of the 500 lakes in Banff, only about six have bull trout in them.

Meanwhile, officials have an even more counterintuitive proposal for Bighorn Lake, also in Banff: remove all fish and leave the lake fishless because that's how the lake was originally.

Both plans are part of a nationwide Parks Canada policy, instituted in 1994, of restoring ecosystems to their natural state, to the extent possible. Experimental restorations involving plants have been undertaken before, but the efforts in Banff are a first for fish. Similar fish-removal exercises have been undertaken in the United States, with mixed results.

The bull trout is Alberta's official fish, but its population dwindled as a result of stocking Banff's lakes with rainbow trout and other "pretty Eastern fish," which were meant "to keep anglers happy," says Charlie Pacas, an aquatic specialist at the park.

Representative ecosystems

The idea is not only to improve habitat for the bull trout - a species considered threatened in Canada, and endangered in some parts of the US - but also to preserve at least a few representative ecosystems in their natural state. The goal is to have some "reference systems" for long-term study says David Schindler, an ecologist at the University of Alberta.

The issue of invasive or "exotic" species in an ecosystem is generally the story of how one can't put the genie back into the bottle: Once introduced into an environment, a species can be virtually impossible to remove.

But in Moraine Lake scientists feel they have a good shot at getting the introduced species out, because it is a relatively closed system. "It's a headwater lake, with not a lot of tributaries into it," Mr. Pacas explains.

Moraine Lake is literally an iconic landscape: For many years an image of the high alpine lake graced Canada's $20 bill. On a busy day in the summer, the lake gets 5,000 visitors. Critics say a campaign to purge the lake, even temporarily, could become a public relations nightmare.

"A lot of people see the lake in its majestic beauty without understanding its aquatic systems," says Pacas. "We're working on the ecological integrity argument."

Controversial methods

Still, Pacas says, "People were concerned about methods" of exterminating the fish. "We want to entertain as many options as possible." Pacas says, and he stresses that the methodology will be subjected to peer review.

Among methods that have been considered are explosions under the ice in winter, poison (likely rotenone, once used on bull trout), gill nets, and electric shocks.

Another idea has been to take advantage of the fact that, one on one against other fish, the bull trout can be ferocious predators and extremely capable of holding their own. "They really get into eating other fish," says Pacas. "It's not unusual to catch a bull trout with another fish in its mouth."

But in the big picture, abundant spermatozoa count more than powerful jaws, and the introduced species seem to have an edge during breeding season, scientists say. And so the scientists have considered introducing sterile bull trout to take out the other species: The sterile fish would do the dirty work without getting entangled with interbreeding. And then when the invaders have been cleared out, bull trout capable of reproducing would be introduced.

Still, some say nature must be left alone. "I was in [the town of] Banff this morning and I saw two elk. Each of them had a tag. Every animal you see has a tag or a collar. Sometimes it seems that the animals have been researched to death," says Mr. Hutton, the owner of Moraine Lake Lodge. "Now that's figurative."

(c) Copyright 2000. The Christian Science Publishing Society