Fish out of their own water

Last month's news that the invasive silver carp had crossed the electric barrier in a canal in Chicago ― and were only a short day's swim from invading Lake Michigan ― caused outcries from the outdoor community and tourist industry across the Great Lakes region.

Scientists should find some way to stop the fish! Canals around Chicago should be poisoned to kill all their fish ! Unfortunately, neither of these solutions is likely to work, and neither addresses the real problems with silver carp and other invaders.

Silver carp were brought to fish farms in Arkansas in the 1970s to control excessive algal growth. Like so many other farmed fish, they soon escaped and made themselves at home in our rivers. These voracious plankton-feeders now constitute more than 90 percent of the weight of all fish in parts of the Mississippi, Missouri and Illinois rivers, diverting resources from native fish and wildlife.

This fish is also famous as the jumping carp. For some reason, the sound of an outboard motor or a Jet Ski causes these fish to leap several feet into the air. These large (up to 60 pounds) wet missiles have already injured boaters in the Midwest and make water-skiing a hazardous sport.

Scientific studies suggest silver carp will do well in all of the Great Lakes except Superior. They may seriously damage the lakes' multibillion-dollar recreational and commercial fisheries that have already been harmed by other invasive species, habitat destruction, pollution and overfishing.

There is every reason to believe silver carp will eventually move through the Great Lakes into the Hudson River. Because of habitat loss, zebra mussel invasion and offshore fisheries, the Hudson's plankton-feeding fish are already doing so poorly the Department of Environmental Conservation is about to close the shad fishery for the first time in history, and river herring populations are at 1 percent of historic levels. Adding silver carp to the mix will only further imperil these populations.

Asking biologists to keep silver carp out of the Great Lakes when these fish are at Lake Michigan's doorstep is like asking your doctor to give you a pill to let you run a marathon after you've been smoking for 30 years and are 100 pounds overweight. You're not asking for a cure — you're asking for a miracle. Biologists don't have tools to kill silver carp and leave the rest of the ecosystem unharmed, or to prevent them from swimming those last few miles into Lake Michigan.

So what can we do? Just as in medicine, prevention is more effective than trying to cure a well-established problem. The path to the Hudson open to the silver carp has been used by many other invaders, including the zebra mussel. This path, from lakes Erie and Ontario through the Erie Canal, could be closed by installing an effective barrier on the Erie Canal. .

More importantly, we could do a better job keeping invasive species out of North America in the first place. Despite progress in slowing the movement of invasive species in ballast water and wooden packing, our borders are still open to the arrival of new invaders through the pet, aquaculture and horticulture industries and other pathways exacerbated by global trade.

Solving the invasive species problem will require political action at the federal level, yet our government does not give high priority to preventing invasive species.

Cary Institute of Ecosystem Studies | Millbrook, New York 12545 | Tel (845) 677-5343

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