New compound may expand sea lamprey control


Michigan State University assistant professor Anne Scott is testing a new method of controlling parasitic sea lampreys in northern Michigan streams. Image: Anne Scott

By: Ben Eiler

A newly discovered chemical compound that makes it difficult for invasive sea lamprey to find their breeding grounds may be a new tool in the toolbox for controlling a parasite that threatens Great Lakes fish.

Anne Scott, an assistant professor at Michigan State University, and her team of researchers are creating a new method of sea lamprey control using a newly discovered chemical compound, petromyzonol tetrasolfate – also known as 3sPZS.

It is very similar to a pheromone that male sea lampreys release in rivers and streams before breeding. The natural pheromone attracts females ready to breed to the males’ nests. But when 3sPZS is released into a river system, females can’t find the nests and are unable to breed, Scott said.

A long process lies ahead for the researchers before this new method can be used. Efficacy tests, like those that prescription drugs must undergo and trial applications in diverse river systems are the next steps of this journey.

The tests are promising and the new compound seems both safe and effective, Scott said. It will naturally break down in the water and due to its similarity to the naturally occurring pheromone, it only influences the invasive sea lamprey.

Sea lampreys are invasive parasitic eel-shaped fish that have been present within the Great Lakes for over 100 years. They latch on to the sides of fish with their suction cup-shaped mouth, pierce fish’s skin with their tongue, and after secreting a blood-thinning enzyme, drain the fish’s fluids. In the Great Lakes and surrounding water bodies, sea lampreys kill 40 to 60 percent of their hosts. This can translate to over 40 pounds of fish killed per lamprey.

Old foe

“Sea lampreys have been present in Lake Ontario since the 1830s,” said Marc Gaden, the deputy executive secretary of the Great Lakes Fishery Commission. It was not until 1921, after improvements to a canal that connected Lake Ontario to Lake Erie, that the lamprey began to spread uncontrollably, he said. “By 1939 there were sea lampreys in every lake.”

Not long after their arrival, the lampreys had a massive effect on the Great Lakes fishing industry. At the height of their populations, between the 1950s and 1960s, sea lampreys had reduced the annual pounds of fish caught in the lakes by 98 percent, Gaden said. This led to a huge effort to control the lamprey population by employing many different techniques.

Of these, the most effective has been the application of a lampricide, 3-trifluoromethyl-4-nitrophenol, also known as TFM. It is used to kill the lamprey larvae before they develop into adults and leave the rivers and streams where they hatched.

Scott describes TFM as “the cornerstone of the control program,” but she says that it has limitations.

The lampricide requires a strong flow through the river, she said. If there are dams or pools in any place along the river, the chemical can get trapped, rendering the treatment ineffective. The treatment must be carefully applied to not have any effect on the native fish populations.

Barrier strategy

Another management option is using natural or artificial barriers to restrict the lampreys from accessing their spawning ground and to reduce their spread into new water bodies. While barriers are quite effective, they may not be a permanent solution.

“There is a large push throughout the Great Lakes and beyond to restore connectivity to our systems. In some areas, folks are advocating for removal of barriers,” Scott said. This could lead to increased populations and spread of sea lamprey.

However, these two methods and others have helped managers reduce lamprey populations by an average of 95 percent in all the Great Lakes, Gaden said.

While this is a huge success, the work is far from over. The Great Lakes Fishery Commission and its partners spend around $25 million each year on sea lamprey control to preserve a fishery that is worth over $6 billion,” Gaden said.

“I don’t think that there’s a control tactic that exists at this point that’s a silver bullet,” Scott said. However, the addition of 3sPZS will make it easier “to tailor some of our approaches to certain streams and especially make sure that we have tactics in place for those more problematic systems.”Scott and her team will continue with their research of this new compound and of sea lampreys as a species. Links to Scott’s published research papers are here.

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