Great Lakes Fishery Commission

Updated 2026-08-20 15:05:50

Lake Huron -> 1.0 Salmonine (Salmon and Trout) -> Lake Trout Mean Age

1.2.2. Mean age of Lake Trout from northern main basin and offshore stocks greater than 9.5 years

Increasing age of stocked fish was expected to be one of the first signs of Lake Trout recovery.  An increasing trend in mean age requires good survival, so that the spawning population builds numbers over time, thereby improving spawning success and production of wild fish.  Target age was defined as 1 year older than the age of first maturity, indicating several cohorts had survived and were spawning together.  During the first 12-14 years after stocking was initiated, target mean age for populations comprised mainly of hatchery-origin fish was set to 7.  After 14-24 years of stocking, when wild fish were expected to comprise a greater proportion of the population, a mean age of 9.5 for wild fish was used as the restoration target for Lake Trout stocks that spawned in the northern main basin and on offshore reefs (Ebener et al. 1998).

As expected, mean age of Lake Trout in the northern main basin and offshore areas increased steadily over time, with most stocked (hatchery-origin) fish reaching or exceeding the target age (7) by the middle 2000s (Figures 1-4).  Mean age of most wild populations during the current reporting period was less than the target age (9.5), but if observed increases in age of wild fish continue, mean age of many wild populations is likely to reach the target within the next five years.  The one exception is in Ontario waters, where mean age of wild Lake Trout has exhibited a declining trend since 2017 (Figure 3).  Yankee Reef/Six-Fathom Bank was the only sampling location where mean age of wild fish met the target during the current reporting period (Figure 2).  Mean age of wild fish on these offshore reefs exceeded the age-9.5 threshold for the first time in 2014 and was at or above target during 2018, 2019, 2021, and 2022 (Figure 2).

Increasing age of Lake Trout is strong indicator that adult survival in the northern main basin is good.  If so, numbers of adult lake trout at spawning reefs should continue to increase, which should accelerate wild production and progress towards reestablishment of self-sustaining populations.

Figure 1. Mean age of hatchery-origin and wild Lake Trout sampled from Michigan waters of the northern main basin, Lake Huron (Assessment survey: Michigan Department of Natural Resources spring gill net survey).

Figure 2. Mean age of hatchery-origin and wild Lake Trout sampled from the 6-Fathom Bank-Yankee Reef offshore reef complex, Lake Huron (Assessment surveys: United States Geological Survey Six-Fathom Bank-Yankee Reef spring gill net survey: United States Fish and Wildlife Survey fall spawner survey).

Figure 3. Mean age of hatchery-origin and wild Lake Trout sampled from Ontario waters of the northern main basin, Lake Huron (Assessment survey: Ontario Ministry of Natural Resources summer gillnet survey).

Figure 4. Mean age of hatchery-origin and wild Lake Trout sampled from the Drummond Island reef complex in northern Lake Huron (Assessment survey: Sault Tribe Gigoonh (fish) community survey).