Factors affecting year-class strength and growth of lake whitefish (Coregonus clupeaformis) and lake trout (Salvelinus namaycush) in the Smallwood Reservoir, Labrador Canada

Year class strengths and growth rates for lake trout Salvelinus namaycush and 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.;Long-term recruitment patterns for both species were influenced by winter draw-down levels: If water levels during February were above average, recruitment was stronger and if levels were lower, recruitment was weaker. Incorporating the additional variable of February water level fluctuations into catch curve regression equations for lake whitefish and lake trout, an additional 10% and 22% in recruitment variability became apparent.;Using width measurements between annuli of otoliths it was determined that growth rates for both species were also influenced by the initial years of impoundment. Lake whitefish experienced the fastest growth rate increases during the initial period of flooding (1971 to 1975). Rates of growth during this time period exceeded the long-term average and were faster than any other five year period between 1965 to 1995. Increases in growth rate were attributed to a zooplankton bloom which occurred concurrently at the time of reservoir creation. Following the period of exceptional growth, lake whitefish underwent a five year period (1976 to 1980) when growth rates were depressed.;Lake trout growth rates for the period between 1971 and 1980 were slower than the later period, between 1981 to 1985. Increases in growth rates subsequent to 1982 were attributed to the decreased recruitment that occurred between 1972 and 1981. It was hypothesized that the thinning in the lake trout population made available greater resources for those lake trout that remained. In addition, flushing of the reservoir probably returned water clarity to its original state, thereby enhancing food predation opportunities for lake trout.;Comparisons of 649 lake trout and 903 lake whitefish collected from two impounded and three unaltered water bodies located in the watershed revealed both species underwent short term episodic changes in growth and recruitment at the onset of impoundment. Filling of the reservoir was carried out between 1971 and 1974, and during this period there was a concurrent increase in whitefish recruitment above the long term average. Conversely, lake trout had weak recruitment for the 10 years following the initial impoundment (between 1972 and 1983). Year-class numbers from this period accounted for 18% of the sampled catch from the impounded water bodies. Whereas, in the natural water bodies the same number of water bodies contributed 47% to the sampled catch, 29% greater.;I developed a technique based on the incremental calcium deposits of otoliths which can be used as an index to establish a biochronology of growth rates. The index can serve as a cost effective mechanism to assess the impacts that reservoir hydrological cycles have on impacted fish populations.