Great Lakes Fishery Commission

Updated 2023-12-08 14:00:22

Lake Ontario -> 2.0 Offshore Pelagic Zone Goal -> Rainbow Trout

Maintaining or increasing population, recruitment, and growth of adult Rainbow Trout in selected tributaries (New York: Salmon River; Ontario: Ganaraska River).

The number of Rainbow Trout returning to the Ganaraska River, ON, a north-shore river that hosts a self-sustaining population of Rainbow Trout and is not stocked, decreased during this reporting period and was, on average, 5% lower than the previous reporting period (Fig. 1). Self-sustaining populations of Rainbow Trout exist as well in other north-shore tributaries east of Toronto, an area where Rainbow Trout are not stocked.

Growth as indexed by the average weight of Rainbow Trout returning to the Ganaraska River after 2 and 3 years in the lake (hereafter, lake years) trended downward during the reporting period where their average weight (5.33 lbs and 7.28 lbs, respectively) represented 7% and 8% declines from the previous six-year reporting period (Figs. 2 and 3). In contrast, average weights of Rainbow Trout returning to Salmon River Hatchery after 2 lake years (6.36 lbs) increased 11%, while the average weight of fish after 3 lake years (7.81 lbs) during the current reporting period was comparable to the previous reporting period (2008 – 2013).

From 2014 – 2019, average condition of Rainbow Trout was evaluated using angler harvested fish from Lake Ontario and adult fish returning to the Ganaraska River, ON and Salmon River, NY. Condition, as indexed by the predicted weight of a 25-inch fish, was comparable to the previous reporting period across all four indices (Fig. 4). Rainbow condition from 2014 – 2019 in the NY creel (5.86 lbs) was similar to the previous six-year average (5.88 lbs), while values from the ON creel showed a decline in condition of 5% (5.30 lbs from 2008 – 2013 to 5.04 lbs from 2014 – 2019). In the Salmon River, Rainbow condition (5.28 lbs) was 1% lower than the previous reporting period, while fish from the Ganaraska River were 3% lower. The condition of Rainbow Trout has been slowly declining in both the Ganaraska and Salmon River indices since the mid-2000s, reaching their lowest values during this reporting period (2015 at the Ganaraska River and in 2019 at the Salmon River Hatchery; Fig. 4).

Figure 1: Estimated and observed counts of adult Rainbow Trout migrating upstream through the Ganaraska Fishway, Port Hope, Ontario (1974 – 2019).

Figure 2: Average weight (lbs) of Rainbow Trout that have spent 2 years in Lake Ontario measured at the Ganaraska River, ON (1974 – 2019) and the Salmon River Hatchery, NY (1988 – 2019).

Figure 3: Average weight (lbs) of Rainbow Trout that have spent 3 years in Lake Ontario measured at the Ganaraska River, ON (1974 – 2019) and the Salmon River Hatchery, NY (1988 – 2019).

Condition (weight of a 25-inch fish predicted from a length-weight regression) of adult Rainbow Trout returning to the Ganaraska River, ON and the Salmon River Hatchery, NY (1974 – 2019).