Before sunrise last Wednesday morning, a team of U.S. Fish and Wildlife Service scientists were at work in their mobile lab near the LaPlatte River in Shelburne. They were there for the application of TFM, a lampricide designed to kill larval sea lampreys in the LaPlatte.
Sea lampreys are a parasitic species of fish, and the population in Lake Champlain feeds on economically important game fish such as trout and salmon, substantially affecting these species’ populations. These lampreys spend their adult lives in the lake, but swim up into tributary rivers, including the LaPlatte, to spawn. Larval lampreys spend their first four years in these rivers, living in the river’s sediments, before joining the adult population in the lake. This provides an opportunity for wildlife managers to remove several years’ offspring in a river with a single application of TFM.
After testing the river’s water in advance to determine the least amount of TFM needed to be effective, the USFWS team performed the application at Shelburne Falls. The recent low-water conditions made the process challenging, noted USFWS fish biologist Stephen Smith as he worked in the lab last Wednesday morning. First, the low water meant that the river could not be treated above the falls. Low-water conditions also contribute to more substantial daily shifts in river water pH, Smith explained, and this can alter the toxicity of the lampricide. One potential effect of this could be the death of non-target species in the river; as of Nov. 22, Smith reported “less than 50 total (organisms) had been found dead after TFM application.
On Thursday morning, dead larval lampreys had begun to appear along the edges of the LaPlatte near the U.S. Route 7 bridge, where Smith was out monitoring the progress of the application. By Saturday afternoon, more dead lampreys could be seen along the river’s banks.
Prior to TFM application, there had been some concern about potential health impacts of TFM application in the LaPlatte, given the location of a public water intake in Shelburne Bay. An activated charcoal system was brought in to the Champlain Water District treatment facility to remove any TFM that traveled as far as the public water intake.
Regular reports from the USFWS following TFM application showed that, in the current low-water conditions, the lampricide did not the reach the mouth of the river at the bay until Saturday; in fact, the lake and river water were at the same level at times, with bay water reportedly washing back into the river on Friday. By Sunday morning, however, monitoring for TFM levels in the lake was underway. As of Sunday afternoon, no lampricide had been detected in CWD samples, and Monday’s report showed no TFM detected at the CWD intake in northern Shelburne Bay.
For more background information, see previous stories at www.shelburnenews.com.