Lean lake trout are found in spawning condition during spring-summer in lakes Michigan and Huron

Here we report the first observations of the capture of lean lake trout (Salvelinus namaycush) in spawning condition in lakes Michigan and Huron during April–July, which is well outside their normal fall spawning season of September–December. Examination of 5731 lake trout landed by anglers at 56 ports in 2022 and 2023 revealed nine female lake trout possessing body cavities filled with mature, loose eggs and two males in ripe condition. Six fish were hatchery-reared and five were of wild origin. Ages of these fish ranged from 6 to 19 years and, of those where strain could be determined, were members of the Seneca Lake and Lewis Lake genetic strains. Loose eggs were similar in appearance to those found in mature fish in fall on spawning grounds. Histological examination of eggs from four females confirmed all were in some stage of ovarian maturity. Two females had ovulated just prior to capture, and the remaining two ovulated much earlier than the capture date. The adaptive advantage of the alternative seasonal spawning is speculative but may include reduced competition with fall spawners, decreased predation risk for juveniles during winter, and access to greater environmental resources in the early spring and summer.