Growth of Hatchery-Reared Chinook Salmon in Lakes Michigan and Huron Exhibits Limited Spatial Variation but Is Temporally Linked to Alewife Abundance

Chinook Salmon Oncorhynchus tshawytscha were introduced into Lakes Michigan and Huron in the 1960s to diversify recreational fisheries and reduce overabundant, nonnative Alewife Alosa pseudoharengus. Alewife remain the primary prey of Chinook Salmon but have experienced substantial declines in abundance due to reduced food resources and salmonine predation pressure. The movements of Chinook Salmon have been linked to the density and spatial distribution of Alewife, but spatial patterns in Chinook Salmon growth have not been well documented and the temporal relationship between growth and Alewife density has not been evaluated during the current period of low Alewife abundance. We evaluated spatial and temporal variation in growth of Chinook Salmon in Lake Michigan and the U.S. waters of Lake Huron and explored linkages with Alewife density. Von Bertalanffy growth parameters were generally similar for recaptured coded-wire-tagged Chinook Salmon from different stocking locations and different recovery locations. Only a few small differences among stocking and recovery regions were evident, with regions divided into two subtly different groups with shared growth parameters. The small regional differences may be attributable to unique habitat and/or stocking characteristics of specific regions. In Lake Michigan average Chinook Salmon length at age also varied across years and was tightly coupled with annual lakewide densities of age-1 and older Alewife, suggesting that Chinook Salmon growth from 2012 to 2016 was constrained by Alewife density. Our findings are consistent with evidence of lakewide movements associated with foraging and support continued management of Chinook Salmon in Lake Michigan as a single population. Furthermore, similar growth in Chinook Salmon from Lakes Michigan and Huron corroborates evidence that Chinook Salmon move from U.S. waters of Lake Huron to Lake Michigan to feed and reinforces the recent decision to include most fish stocked in northwestern Lake Huron in the Lake Michigan population when managing for predator-prey balance.