Evidence of Widespread Natural Reproduction by Lake Trout Salvelinus namaycush in the Michigan Waters of Lake Huron

Localized natural reproduction of lake trout Salvelinus namaycush in Lake Huron has occurred since the 1980s near Thunder Bay, Michigan. During 2004-2006, USGS spring and fall bottom trawl surveys captured 63 wild juvenile lake trout at depths ranging from 37-73 m at four of five ports in the Michigan waters of the main basin of Lake Huron, more than five times the total number captured in the previous 30-year history of the surveys. Relatively high catches of wild juvenile lake trout in bottom trawls during 2004-2006 suggest that natural reproduction by lake trout has increased and occurred throughout the Michigan waters of the main basin. Increased catches of wild juvenile lake trout in the USGS fall bottom trawl survey were coincident with a drastic decline in alewife abundance, but data were insufficient to determine what mechanism may be responsible for increased natural reproduction by lake trout. We recommend further monitoring of juvenile lake trout abundance and research into early life history of lake trout in Lake Huron.