WHITEHORSE, Yukon Territory (AP) - The sudden disappearance of northern pike from Watson Lake remains a mystery, says a Yukon fishery technician.

The community on the British Columbia-Yukon border went from a destination for anglers in search of trophy pike to a lake devoid of the fish in one year.

In the summer of 2002, anglers caught 1,680 of the fish and kept 158.

Working from 2002 catch-and-release figures, Aaron Foos of the Department of the Environment said it would be reasonable to expect there to be more than 20,000 pike in the lake.

But during the summer of 2003, there were no instances of any pike being caught. Nor did any show up in an intensive search by ministry officials.

However, said Foos, the rest of the fish in the lake - lake trout, grayling, white fish and burbot - are doing just fine.

"It's weird," Foos said.

Watson Lake conservation officer Ryan Hennings received reports of dead pike on the lake's surface last spring but didn't recover any of the reported fish.

When the reports began, Hennings started checking for the normally visible, shallow spawning beds used by pike.

There were none.

"That is when we realized that, yep, we have a serious problem," he said.

Through the summer, the conservation officer intensified his patrols of Watson Lake to speak with anglers.

Fisheries biologist Sue Thompson was dispatched from Whitehorse to the community last July to net for pike.

After 24 one-hour sets, they found lots of other fish but no pike.

Foos said there were no signs of contamination. Besides, he said, something foreign, such as a toxic substance, would likely affect other species in the lake.

There's also no evidence of effects on the pike living in the lake above, and it drains into Watson Lake, Foos said.

AP-WS-04-22-04 1152EDT