Endangered Stonecats in Vermont: A Risk Assessment Approach

Stonecats (Noturus flavus) are designated as a Vermont state-listed endangered species because their distribution is limited to the LaPlatte and Missisquoi rivers. The restricted distribution and lack of knowledge on abundance in either river is cause for concern for their continued survival. The Missisquoi River population has potential for increased intermittent mortalities from lampricide (3-trifluoromethyl-4-nitrophenol) treatment every four years and dewatering during drought conditions. In 2012, 2013, and 2014 we captured, PIT tagged, and VIE marked all Stonecats collected using backpack electrofishing and minnow traps in the LaPlatte and Missisquoi rivers. Stonecats (N=1252) were PIT tagged in the LaPlatte and 125 in the Missisquoi. Few Stonecats were captured in the Missisquoi River, so we used the PVA model to estimate extinction rates with increased intermittent mortalities on 4-, 6-, and 8-year cycles. With an initial number of 2000 individuals, the population became extinct 100% of the time with an increase in mortality of 0.1 on a 4-year cycle. Results indicate that the Missisquoi River population, in the area affected by lampricide, is at risk for extinction. These results are informative for developing future management scenarios, however, our approach has uncertainty that can only be addressed through obtaining more data.