Endangered Stonecats in Vermont: Differential Mortality Effects On the Likelihood of Sustainability

Stonecats (Noturus flavus) are listed as endangered in Vermont, with their known distributions limited to two rivers. In 2012, we captured and PIT tagged or marked 412 stonecats in the LaPlatte River and 64 in the Missisquoi River. The sizes in the LaPlatte ranged from 52-192 mm total length (TL); whereas, the range in the Missisquoi was 56-202 mm TL. Stonecats captured in the LaPlatte were much smaller than those captured in the Missisquoi. A plausible explanation for the differences in population structure is that the Missisquoi population has the potential for increased mortality every four years during application of the lampricide TFM (3-trifluoromethyl-4-nitrophenol). High concentrations of TFM have been attributed to increased mortality of stonecats in other systems. During the 2008 post-treatment assessment in the Missisquoi River, 22 stonecats were found dead. However, in 2012, only 2 mortalities were documented. The concentration of TFM was lower in 2012 than in 2008 when an applicator problem produced an area of high concentration in known stonecat habitat. Our analysis is expected to provide a clearer understanding of the long-term status of the populations and whether TFM treatments can be related to the abundance of stonecats in the Missisquoi River.