"The US Fish and Wildlife Service and the Vermont Department of Fish and Wildlife monitor smelt populations in Lake Champlain. They have not seen any changes in smelt numbers outside the 'normal' levels of fluctuation seen prior to the alewife introduction," Durfey said.
The poor ice fishing catch might have more to do with localized smelt distributions or turbidity, he said.
"In previous years we have observed poor smelt fishing when the water in the Westport and Port Henry areas has become cloudy. But those are just possibilities - we don't really know the cause of the poor fishing, but we do know it was not because there weren't smelt in the lake."
Pientka did acknowledge that alewives are starting to inhabit "margin" areas traditionally inhabited by smelt, which forces smelt to other areas. As an example, he said alewives tend to congregate in warmer regions - like shallow water in summer and deeper water in winter. This drives out the smelt and changes the pattern of forage fish like perch and lake trout.
Pientka concurred, however, that biologists are somewhat stumped as to why catches are down so dramatically.
Also lacking is a full study documenting characteristics of fish populations in winter, Pientka said.
"We're trying to figure it out," he said. "It's really tough when these new species show up because we have very little historical data to draw from."
"We basically are forced into a 'wait and see' approach," he said.
John Gereau is managing editor of Denton Publications. He can be reached at firstname.lastname@example.org