Timothy Kratz, site manager for the NSF-funded North Temperate Lakes LTER in Wisconsin, samples open-water fishes with a vertical gill net. Among the wealth of long-term data gathered from the lakes is evidence of time lags in how "invaders" affect lake communities. For example, in Sparkling Lake a kind of trout called cisco went extinct sixteen years after smelt found their way in.

Photo: North Temperate Lakes/University of Wisconsin LTER