Comparison of Lake Trout Diets Between Day and Night Sampling

Lake trout (Salvelinus namaycush) stocking in Lake Champlain began in 1973. Wild recruitment was not observed in the lake until 2015. The reasons for the recent wild recruitment suddenly starting are currently unknown. Diet analysis has been used to understand lake trout energetics as a potential clue to determine why wild recruitment started. Sampling for diet analysis is commonly done during the day for logistical reasons. However, lake trout feed during the night as well as during the day, and the availability of prey species changes at night. The purpose of this study was to test the assumption that diet data from lake trout collected during the day represents what lake trout eat throughout the 24-hour period. Sampling for juvenile lake trout was conducted using bottom trawling during the day and the night in Burlington Bay, Lake Champlain, in 2018 and 2019. Dissections of the stomachs of lake trout caught during the day and night resulted in comparable percentages of lake trout with food in their stomachs, comparable numbers of total diet items and significant diet overlap. However, the diet of lake trout caught at night had higher biomass and contained larger rainbow smelt (Osmerus mordax), fewer young-of-year fish, and smaller Mysis (Mysis diluviana) than lake trout caught during the day. Overall, daytime sampling provides accurate information on the composition of the diets of lake trout, but not the size of their prey