Monday, May 05, 2008

Tilapia in the Snake

From an aquaculture standpoint, tilapia has much to recommend it: As adults, they're vegetarians, so they require low energy inputs to raise. They are easily raised even in urban tanks, so food production can occur in areas that are already developed rather than degrading natural areas. And they can even be fed vegetable compost, turning household scraps into more food, or even a livelihood. In some African nations, development projects have installed tilapia ponds which are fed by the village's leftover vegetable waste. (A good account of such a project can be found in Mike Tidwell's book, The Ponds of Kalambayi).

But tilapia in Idaho's Snake River? Not so good.

Tilapia are native to Africa, but due to all the good reasons listed above, have been transported for aquaculture around the world. And like many creatures transported to new lands, they inevitably escape.

Recently, the Idaho Statesman reported the catch of a state record tilapia in the Snake River. Perhaps your reaction is like mine: There are tilapia in the Snake?

Actually, they've been there for a while, living in areas near thermal springs. Tilapia need warmer water temperatures to survive, so it's unlikely that they'll spread--unless, of course, water temperatures rise due to a changing climate.

In other rivers around the world, tilapia can become a menace. As vegetarians, they devour all aquatic vegetation, eliminating the base of the aquatic food chain. According to the U.S. Geological Survey, rivers that have abundant tilapia have lost nearly all their native fish.

Will this happen to the Snake? Probably not for now. But with any non-native species, the real impacts are often not apparent until it's too late. Some never become a problem, and may even be beneficial. Others spread rapidly and become impossible to control. New Zealand mudsnails were found in Silver Creek several years ago, but the cold water there is limiting their spread. In other streams, they have crowded out much of the native invertebrates, and thus, the fish.

The easiest way to stop the spread of such species is to prevent their introduction. But that is difficult in a global society. And anywhere where non-native creatures are raised, there's always the risk that they'll escape. The tilapia is already likely a permanent part of Idaho's aquatic fauna. The question is: Just how much a part will it be? --Matt Miller

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