Dead lampreys had appeared in the river by the day after treatment. Photo by Lauren Milideo

A couple of weeks ago, workers from the U.S. Fish and Wildlife Service treated the LaPlatte River with TFM, a lampricide or pesticide used to kill sea lamprey larvae. Monitoring of water for TFM levels in the river and Lake Champlain, which commenced when treatment began, ended this Monday, with no TFM detected in raw or finished water at the Champlain Water District, according to data released by the USFWS.

Sea lampreys in Lake Champlain are parasitic, wounding such game fish as salmon and trout. They breed in surrounding rivers, and larval sea lampreys remain in these rivers for their first four years. TFM application in the LaPlatte killed larval lamprey before they “get to that ripe age where they can head out as parasites,” noted USFWS Sea Lamprey Control Program Manager Brad Young.

The treatment was a success, Young said. The survey crew was surprised at the number of lampreys killed by the treatment: “it exceeded our expectations regarding the number of lamprey that probably were residing in there based on the survey that we did.” Young added that while it’s not possible to know the exact number of lampreys killed, he estimated a minimum of thousands.

One concern regarding TFM treatment was the potential detrimental effects on other species. USFWS monitoring following treatment revealed that individuals of several species, including the stonecat fish, which is endangered in the state according to the Vermont Fish and Wildlife Department (though not federally endangered), had died during the course of post-treatment survey. Young noted that the stonecat deaths – perhaps 33 total, though data have not yet been finalized – possibly resulted from a long exposure time to TFM. Stonecats have been tested for 12-hour TFM exposure, but the recent LaPlatte treatment was 14 hours long.

“The stonecats were fine until hour 13 out of 14. And in hour 13 they started popping up, just all of a sudden, like in a mass,” Young said, noting that stonecats may react differently to TFM than lampreys, which have been tested for 20-hour exposures and show little change in reaction after nine hours of exposure – either the treatment concentration has killed them after nine hours, or it will have no further effect. The longer treatment time was used here to establish a sufficient dose to kill sea lamprey larvae. A shorter exposure time may be in order for future treatments to preserve stonecats, Young noted. Young also pointed out that a slightly lower concentration of TFM was used than had been authorized.

Young also noted that about 125 stonecats were removed from the river by USFWS workers, and returned to the river following treatment.

Though data are still being analyzed, preliminary results show that other species killed include leopoard and green frogs, brown and yellow bullfrogs, and minnows. Each of these species had fewer than 10 individuals killed; some had only one individual found dead. Young noted that this was an acceptable result – especially considering that in any natural ecosystem with thousands of organisms, a few dead animals will always exist.

“On any day of the week you could walk down the river, and find dead things in the river without a treatment. That’s not that uncommon,” Young said, adding, “The very small numbers of other species is completely expected and they may or may not have been affected by the treatment. And at any given time, there’s individuals that are sick or stressed or for whatever reason just not as healthy as other ones and they may be more susceptible than others.”

Another concern of TFM treatment in the LaPlatte was the potential of TFM reaching the CWD public water intake in Shelburne Bay. The TFM was not detected in raw or finished water, but a mobile activated charcoal removal system had been brought in to treat the water just in case. Handling these concerns presented new challenges, Young acknowledged.

“Comparing this to other treatments, this was the highest amount of time spent in preparing and planning a treatment that we’ve ever spent. And it’s not a very big river.” But help also came from multiple agencies, including the governor’s administration and CWD.

“The people at CWD were fantastic,” Young noted.

Going forward, Young hopes to see a decrease in the sea lamprey wounding of game fish in Lake Champlain. “The fishermen I’m hoping are going to see a difference in the number of lamprey not only in Shelburne Bay but in all of Lake Champlain this year,” Young noted, adding that a study of wounding rates next fall will reveal more about the treatment’s full impact on salmon and trout.

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