Science: Death for Baby Lampreys

Poisons for killing off plant and animal nuisances are rapidly becoming more selective, so that they do their job without hurting species that man wants to preserve. Last week Dr. James W. Moffett of the U.S. Fish and Wildlife Service was getting encouraging results with a selective chemical designed to deal with the predatory eellike sea lamprey which has invaded the Great Lakes and almost exterminated the valuable lake trout (TIME, May 9). The lamprey, which bypassed Niagara Falls via the Welland Ship Canal, attaches itself to fish with a tooth-armed sucker and bores and sucks them to death. It has done so much damage to lake fisheries that the U.S. and Canada are spending large sums to cope with it.

The lamprey’s chief weakness is its breeding system; the adults (up to 2 ft. long) swim up rivers in early spring to spawn. The young lampreys, which look like minute worms, bury themselves in mud and lead a wormlike life, eating microorganisms. After five years of this, when they are 7 in. long, they develop toothy suckers and drift downstream to hunt fish in the lake.

U.S. and Canadian lamprey fighters have had some success with electrically charged fences built across the lampreys’ favorite streams. Adult lampreys are killed or driven back by the electricity before they can spawn, but good fish are affected, too, and the fences are expensive to build and operate. Dr. Moffett felt it would be much better to find some chemical that would kill the infant lampreys in their burrows. The poison would have to spare the desirable fish that use the same streams, and no such chemical was known. So Moffett sent out a call for help, asking universities and industrial companies to send him chemicals that might do the trick. In the last 2½years, the Hammond Bay Fishery Laboratory near Rogers City, Mich, has tested more than 5,000 of them. Out of this laborious screening has come a single compound that kills infant lampreys without hurting rainbow trout or bluegill sunfish. It is now being tested on other fish, and if it stilllooks good, next summer when the streams are low it will get a full-scale test.

The beauty of chemical treatment for lampreys is that it will kill five hatches at once The adults spend only one year in the lakes returning to the streams to spawn and die. If the poison were used liberally for two years in succession, it might make Great Lakes lampreys as scarce as bison.