Great Lakes Fishery Commission

Updated 2026-08-20 14:58:41

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

1.2.3. Mean age of Lake Trout from the southern main basin, Georgian Bay, and North Channel greater than 8.5 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 8.5 for wild fish was used as the restoration target for Lake Trout stocks in the southern main basin, Georgian Bay, and the North Channel (Ebener et al. 1998).

Mean age of Lake Trout in Ontario waters has not consistently reached target levels.  For example, in Ontario waters of the southern main basin, age of hatchery-origin Lake Trout exceeded the recovery target (8.5 years) in three of the last 4 years of the current reporting period, but age of wild trout was above the recovery target only 3 times in the entire data series and did not reach target levels during any year of the current reporting period (Figure 1).  Age of Lake Trout in Georgian Bay has exhibited multiple periods of growth and decline.  Age of wild trout exceeded the recovery target in 2008, and did so before hatchery-origin fish, which did not reach the recovery target for the first time until 2013 (Figure 2).  After briefly achieving the recovery target, age of both groups underwent periods of decline:  through about 2015 for wild fish and through 2017 for hatchery-origin fish (Figure 2).  Thereafter, age of Lake Trout in Georgian Bay increased again, but age of wild fish was less than the recovery target each year of the current reporting period and age of hatchery-origin fish reached the target threshold only in 2021 (Figure 2).  Likewise, age of Lake Trout in the North Channel has fluctuated erratically, and during the current reporting period, mean age exceeded the recovery target only in 2019 for wild fish and only in 2021 for hatchery-origin fish (Figure 3).

In contrast, mean age of Lake Trout in Michigan waters of the southern main basin met age targets during the current reporting period.  Mean age of hatchery-origin fish first met the age-7 target in 1992 and has been consistently above this threshold since 2004 (Figure 4).  Likewise, age of wild Lake Trout sampled from Michigan waters of the southern main basin first exceeded the target age (8.5) in 2007 and was above target each year during the current reporting period (Figure 4).

Lack of sustained growth in the mean age of Lake Trout in the southeast main basin, Georgian Bay, and the North Channel suggests that mortality in Ontario waters is occasionally too high to sustain growth of spawning populations.  Recently the Ontario Ministry of Natural Resources (OMNR) paused stocking in Georgian Bay to determine if mean age will increase after young, stocked fish are no longer entering the population.  In contrast, OMNR recently increased stocking rates in the North Channel to boost population size of hatchery-produced fish.  Monitoring in both areas will be critical to understand whether trout abundance can be maintained, and to determine if production of wild fish production is sufficient to reduce or eliminate stocking.

Figure 1. Mean age of hatchery-origin and wild Lake Trout sampled from Ontario waters of the southern main basin, Lake Huron (Assessment survey: Assessment survey: Ontario Ministry of Natural Resources summer gillnet survey).

Figure 2. Mean age of hatchery-origin and wild Lake Trout sampled from Georgian Bay, Lake Huron (Assessment survey: Assessment survey: Ontario Ministry of Natural Resources summer gillnet survey).

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

Figure 4. Mean age of hatchery-origin and wild Lake Trout sampled from Michigan waters of the southern main basin, Lake Huron (Assessment survey: Michigan Department of Natural Resources spring gillnet survey).