Carelessness exposes native species to alien invasion

July 14, 2002|By Bob Bock

A SMALL Crofton pond is ground zero for a biological invasion that could be disastrous.

Someone dumped into the pond a nasty fish that eats everything in sight -- fish, frogs and even birds.

The fish, the northern snakehead, can slither over land to other bodies of water and, unchecked by the predators of its native waters in China, might cause the extinction of a number of local species.

A Maryland resident dumped two northern snakeheads into the pond more than two years ago because they no longer were wanted as pets, Department of Natural Resources police said.

The Sun reported July 3 that Walter Courtenay of the U.S. Geological Survey may seek a federal ban on importing the snakehead into this country. A ban is a good idea and would help to protect our aquatic life from the carelessness of a few people.

But a ban won't solve the larger problem we face.

Along with pollution and habitat loss, alien species -- those that people transplant from one location to another -- pose a threat to the plants and animals found naturally in North America. Alien species have caused environmental disasters everywhere they have been introduced to new homes. For example, zebra mussels multiply uncontrollably, scouring waters of microorganisms that feed the young of sport fish.

Another example was available at the Crofton pond.

While trying to net baby snakeheads, I came across some bluespotted sunfish. These beautiful, delicate creatures don't grow much larger than a silver dollar. Male bluespots have fluorescent blue spots and build nests to tend their young. These could be the last surviving bluespots from that pond. If the snakeheads don't eat them, it's possible they may be eradicated by attempts to remove the snakeheads.

Anglers can do their part by not moving fish from one body of water to another. Transplanted largemouth bass have nearly eliminated many fish native to the desert springs of the United States and pushed others into extinction.

A well-meaning act like releasing bait fish after a day's fishing may also have dire consequences.

Red shiners liberated from bait buckets into the Colorado River carried with them a parasitic tapeworm. The tapeworm spread to the woundfin, a native minnow. Not as resistant to the tapeworm as were the shiners, the woundfin suffered a rapid decline from which they have barely recovered.

Likewise, home aquarists should never release their pets once they grow tired of them. The Everglades is now full of tropical fish that escaped from the aquarium trade. The tropical invaders prey on some local species and compete with others for food and territory.

Whether a species has economic value or is simply worthy of our appreciation, we'll never gain any benefit from it once it's gone.

But carelessness is something all of us can avoid by never releasing captive plants and animals into the wild.

Bob Bock is past president and a current board member of the North American Native Fishes Association. He lives in Silver Spring.

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