Retrospective growth analysis of lake whitefish (Coregonus clupeaformis) in Lakes Erie and Ontario, 1954-2003
Lumb, C.E.; Johnson, T.B.
Recent declines in growth and condition of lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes has been attributed to ecological change largely associated with invasive species and the loss of Diporeia, an energy rich prey item. We reconstructed growth and diet for lake whitefish in Lakes Erie and Ontario over a 50-year-time period to explore the consequences of large-scale ecological change on growth rate potential for lake whitefish. Analyses were undertaken for three distinct time periods: (i) pre-phosphorous abatement, (ii) post-phosphorous abatement but pre-dreissenid invasion, and (iii) post-dreissenid colonization. Decreased growth rate in the first two years of life was observed in both lakes when comparing the post-dreissenid time period with the pre- and post-phosphorous abatement time periods. Changes in early growth persisted through adulthood. Based on bioenergetics modelling, growth was more sensitive to diet composition than differences in water temperature. Analysis of stable carbon and nitrogen isotopic ratios from archived scales showed a significant decrease in the carbon signature in the post-dreissenid period, suggesting a more pelagic carbon source than in the past. Growth of lake whitefish was limited by potential of older fish to compensate for depressed early growth following largescale changes in productivity and resource availability.