Energy dynamics of Lake Michigan chinook salmon

There is evidence the Great Lakes chinook salmon, particularly those in Lake Michigan, are vulnerable to over-winter depletion of energy reserves. Many biologists believe the large increase in chinook natural mortality rates that occured in Lake Michigan in the late 1980s was due to this stress.  Consequently, fishery managers seek reliable indicators of future nutritional stress in chinook salmon populations. 

We collected wild-ranging chinook salmon from Lake Michigan and measured various indicators of fish nutritional state in fall and spring over a three-year period (Fall 2000 - Spring 2003). Measures of nutritional state included total lipids and lipid components, energy content, water content, protein, stomach contents, and levels of Renibacterium salmonarum in kidney tissue. Results were evaluated by season, size category (small, medium, large), sex, maturity status, and location of colletion.  

We observed little seasonal change in protein levels.  We did find significant seasonal changes in lipid and water levels in both the whole fish tissue and muscle tissue.  Overall, small fish in the spring had the lowest lipid levels and we concluded that these fish are most prone to nutritional stress during the winter.  We also found that in large fish, lipid levels decreased from the spring to the fall of the year in which they matured.  Since lipids are costly and time-consuming to measure, we also looked at surrogate measures for whole fish lipids.  We found that measuring water content in the muscle tissue is an adequate surrogate for whole fish lipids, especially when we are concerned about nutritional status of an entire population.  These results led us to propose a monitoring program for nutritional stress in Lake Michigan Chinook salmon (Peters et al. 2007).  A final portion of this project involved building a bioenergetic and dynamic programming model which looked at how the different environmental conditions that Chinook Salmon face in Lake Michigan, compared to their native environment of the Pacific Ocean, would affect optimal energy allocation strategies in the two environments.

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