Fish in Lake Laberge are a lot healthier these days. Contaminant levels in burbot and lake trout have dropped drastically over the last decade, and there are also more lake trout swimming around.

Researchers think that these two findings are linked, and this summer they have been running an extensive testing program to test the connection. In fact, the recent history of Lake Laberge clearly illustrates how much links matter in the environment, both globally and at the local level.

In 1990 Environment Canada ran a routine series of tests on fish in the lake, and found surprisingly high levels of organochlorines in burbot and lake trout. These nasty chemicals persist in the environment and can cause a range of health problems, so finding such high levels in Yukon fish shocked many people.

Mark Palmer, the contaminants manager for the Department of Indian Affairs and Northern Development, is in charge of the current testing program. He says that when the original tests were run a decade ago, no one was expecting these sorts of results.

"It was part of an on-going study. You have to remember that contaminants were just starting to be an issue. In the Yukon it was the first real case showing long-range transport of contaminants."

Toxaphene, the main contaminant, was blowing in on the wind from other parts of the world. This agricultural pesticide, which was regularly used to treat cotton in the southern United States, is now banned in the U.S. and Canada.

Palmer said toxaphene was used only once in the Yukon; in the early 1960s fisheries officials attempted to kill jackfish in a lake in the central Yukon with it. But it is still used in countries such as Russia which are upwind of the Yukon, and in Lake Laberge toxaphene levels were so high that the Yukon's medical health officer advised people not to eat many lake trout or any burbot livers from fish caught there.

The news was a blow for First Nations people as burbot livers are a prized delicacy in their culture. PCBs and DDT were also found in the fish, and while these chemicals were used in the Yukon, Palmer said that most of the stuff in Lake Laberge came here from parts unknown.

After the Lake Laberge findings, fish from other southern Yukon lakes were tested, as well as those in Atlin Lake. Organochlorines were also found in these fish, but none had levels as high as the fish from Lake Laberge. Contaminant levels there were two to ten times higher than in other lakes tested.

Lake Laberge also had fewer lake trout compared to similar lakes, and lots of burbot and longnose suckers. In Kluane Lake, for example, about 30 percent of the fish were lake trout, while only seven percent of the fish in Lake Laberge were lake trout and half were suckers.

Lake trout from Lake Laberge are highly prized for their firm meat, a product of the cold deep waters in which they live. But they also grow slowly there, and are vulnerable to overfishing.

In an attempt to rebuild stocks, the commercial fishery for lake trout in Lake Laberge was closed in 1991. Sport fishing and the aboriginal subsistence fishery were voluntarily reduced.

The numbers of lake trout have almost doubled since then, and now the Department of Indian Affairs and Northern Development is trying to determine whether the increase in fish numbers has led to the decrease in contaminants.

Snow and air monitoring programs showed that all parts of the Yukon get about equal shares of contaminants; levels only increase in areas with more snow. Since there was no local source for the chemicals in Lake Laberge, there had to be another reason why the fish were so heavily contaminated.

"We thought that there was something in the lake that made it special," says Palmer. "The theory was that the lake was overfished."

Lake trout are big fish, and when their numbers are low, they can eat pretty much what they please. Instead of lowly fare like invertebrates, the lake trout can dine on small fish.

"If you have a small population of lake trout, they can eat high on the hog," explains Pat Roach, a contaminants scientist with DIAND. "The fish did not have to go as far down the food chain to eat, so they accumulated more fat and more organochlorines."

While organochlorine levels in Lake Laberge fish have dropped about five-fold over the last decade, contaminant levels in fish from other lakes have remained about the same. Now, for example, fish from Kusawa Lake have higher levels of toxaphene than those from Lake Laberge.

It is not yet known whether fish in Lake Laberge have substantially changed their diet. The hope is that this summer's research will lead to a lifting of the health advisory, and that once again people will not have to worry about eating lake trout and burbot from the waters of one of the Yukon's most famous lakes.

For more information on the Lake Laberge testing program, contact the DIAND contaminants division at 667-3272. Mark Palmer can be contacted at palmerm@inac.gc.ca.