PREDATOR CYCLES. Sometimes, the invasive species become part of the food chain.

Native walleye appear to be surviving the quagga invasion, and native lake trout seem to have adapted to eat round gobies, another freighter-borne invader that eats quaggas. Lake trout are what now sustains [Lake Huron fishing captain Janice] Deaton's charter business.

The fact that these two native species appear to be outlasting the more popular exotic salmon give conservationists some hope.

"There are native species left," says Jennifer Nalbone of the conservation group Great Lakes United. "There is some integrity to the system left, and it's our responsibility to protect it."

[National Oceanographic and Atmospheric Administration scientist Gary] Fahnenstiel says there is a chance [Lakes Huron and Michigan] can ultimately reach a balance with the invaders where they will have a self-sustaining but less productive - and lucrative - recreational fishery.

Self-sustaining does not rule out population fluctuations. We've already noted that Erie Island sea snakes also snack on gobies.