Lake Trout population dynamics on Six Fathom Bank and Yankee Reef in Lake Huron, 1992–2023

Abstract Objective Under the auspices of the Great Lakes Fishery Commission, the Lake Huron Committee and its technical committee initiated offshore stocking of Lake Trout Salvelinus namaycush beginning in 1985 as an additional step toward restoring a self-sustaining Lake Trout population to the lake, with stocking occurring first at Six Fathom Bank and then later at Yankee Reef. The goal of this study was to assess progress toward Lake Trout rehabilitation on Six Fathom Bank and Yankee Reef in Lake Huron through 2023. Methods We conducted annual (1992–2023) gill-net surveys in the spring–summer and the fall to assess juvenile and adult populations, as well as beam trawl surveys in the spring–summer to detect naturally reproduced age-0 Lake Trout. Result During 2000–2015, relative abundance of unclipped (wild) Lake Trout surged from levels of <2 fish · 305 m of gill net−1 · d−1 to levels exceeding 50 fish · 305 m of gill net−1 · d−1 on both Six Fathom Bank and on Yankee Reef, based on fall gill-net surveys, and has remained at a relatively high level through 2023. The proportion of wild fish in both the spring gill-net surveys and the fall gill-net surveys averaged well over 50% in the Six Fathom Bank–Yankee Reef (SFBYR) complex during 2014–2023. Sea Lamprey Petromyzon marinus wounding rate in the SFBYR complex decreased from 20 wounds/100 fish during 1994–2002 to just 7 wounds/100 fish during 2004–2023, based on the fall gill netting. Annual mortality rate estimates for SFBYR adult Lake Trout during the 2004–2023 period averaged 21%. Wild age-0 Lake Trout were captured in beam trawls in the SFBYR complex during the 1994–2022 period, providing further evidence that Lake Trout were actively spawning within this offshore reef complex. Conclusion Based on several metrics, the SFBYR Lake Trout population appeared to be self-sustaining. Lake Trout stocking, Sea Lamprey control, and restrictions on fishing for Lake Trout played important roles in the population recovery. The lessening of the negative effect of Alewives Alosa pseudoharengus on Lake Trout natural recruitment was likely a key factor in the restoration process.