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. 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. The theory was that 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. 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.