Assessing limitations on reintroduction success: the influence of spawning habitat and thiamine deficiency on Atlantic salmon in Lake Champlain

With the decline of freshwater fish populations, reintroductions are becoming more prevalent. In this study, we evaluated two limiting factors on the reintroduction success of Atlantic salmon (Salmo salar) within the Lake Champlain Basin: 1) the effects of dam removal on spawning habitat availability; and 2) the influence of thiamine deficiency, caused by the consumption of non-native alewife, on the survival and behavior of salmon embryos. The removal of the Willsboro dam increased availability of spawning habitat for Atlantic salmon by allowing them to access large areas of good quality habitat upstream of the former dam site and improving the quality of the small area of habitat available downstream. However, reproductive success may still be limited by thiamine deficiency. High young-of-the-year mortality occurred in families with egg thiamine levels up to 8.5 nmol/g, indicating a larger influence on recruitment then previously thought based on the 1.1nmol/g threshold for Atlantic salmon given in the literature. Though we did not find any behavioral evidence to suggest low thiamine embryos could not partake in early feeding, which may help to naturally mitigate the effects of the deficiency, recruitment remains low within the basin, suggesting the potential need for more controlled management. While this study helps to fill a gap in the literature on reintroduction monitoring and demonstrates the complex nature of population reestablishment, the results also contribute to the overall knowledge on dam removal and thiamine deficiency, which can be applied to research and management outside of the framework of reintroductions