If you've spent much time around North America's Great Lakes, then you're probably familiar with the sea lamprey. The eel-like fish first made its way into the lakes from the Atlantic Ocean in the early 20th century, via shipping canals. Since then, it's become a destructive invasive species, depleting stocks of native fish by parasitically feeding on their blood. Thanks to recent research, however, there may be new hope for controlling lamprey populations – and it involves turning one of their natural defence mechanisms against them.

Currently, the main approach to lamprey control involves adding a chemical "lampricide" to the tributary streams that serve as lamprey nurseries. The chemical is designed to kill larval lampreys, while not harming most other aquatic organisms. According to a team at Montreal's Concordia University, though, administering lampricide is a costly and labor-intensive process, plus there are concerns that it could harm the ecosystem.

Low concrete dams have also been built across the mouths of the tributaries, which the poorly-jumping adult lampreys have difficulty getting past when swimming upstream to breed. Again, though, building dams isn't a simple or cheap process. Additionally, although the dams are typically equipped with sneak-around "fish ladders" at the sides, it's possible that native species of fish will likewise be thwarted by the structures.

That brings us to the Concordia scientists' latest research. They've collected a compound that lampreys emit into the water when frightened or injured, which alerts other lampreys to stay away because danger is nearby. It had previously been suggested that this substance could be used to keep lampreys away from their own spawning grounds, thus stopping them from reproducing.

In a recent test of that theory, a team led by Prof. Grant Brown tagged hundreds of lampreys with transponder tags, then released them near the mouth of a large stream – not far up that stream, a nursery tributary flowed into the main stream. Initially, 60 percent of the lampreys swam up the main stream, while 25 percent proceeded to swim up the tributary.

The scientists then added the "alarm cue" extract to the water in the tributary, allowing it to flow down into the main stream. Once they had done so, only 40 percent of the tagged lampreys entered the main stream, and only 3 percent swam up the tributary.

It is now hoped that the system could be combined with the use of pheromones that lampreys use to attract mates. In this way, the fish would be both scared away from their spawning grounds and drawn to another location, where they could then be trapped.

The research, which also involved scientists from Ontario's Algoma University and the United States Geological Survey, was recently described in a paper published in the journal Fisheries Management and Ecology.

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