Factors affecting year‐class strength and growth of lake whitefish (Coregonus clupeaformis) in impounded lakes as revealed by otolith chronologies

Recruitment and growth rates for lake whitefish (Coregonus clupeaformis) inhabiting the Smallwood Reservoir, Labrador, Canada, were influenced by facets of its creation and the temporal variability in water levels associated with its operation. Filling of the reservoir between 1971 and 1974 created a concurrent increase in lake whitefish recruitment above long‐term averages. In addition, recruitment was influenced by winter drawdown levels: higher water levels during February enhanced recruitment, accounting for an additional 10% of the long‐term variation in recruitment. Using otolith increments as a growth index, the authors determined that growth was influenced by reservoir creation. Growth rates during the initial period of flooding (1971–1975) exceeded long‐term averages and were greater than those in any other 5‐year period between 1965 and 1995. Growth rate increases were attributed to a simultaneous zooplankton bloom. After exceptional growth, lake whitefish showed a period (1976–1980) when growth rates decreased. The authors developed a quantitative technique using otoliths as an index to establish chronologies of fish growth rates. The index can be used to quantify and assess the impacts of reservoir hydrology on fish populations.