The feasibility of the restoration of Atlantic salmon (Salmo salar) into the Lake Ontario basin

Efforts to restore Atlantic salmon (Salmo salar) in Lake Ontario have continued since the species was declared extinct in the late 1800's. All attempts to establish self-sustaining populations have failed but the reasons for the unsuccessful re-introduction remain unclear. In an attempt to better evaluate the feasibility of the re-introduction of Atlantic salmon in Lake Ontario, I studied 2 aspects of the early life history of Atlantic salmon (embryos' survival and interspecific competition). I also used the information obtained during my embryos' survival study to determine if the SIDO model, a model which predicts survival at emergence, could be used as a management tool in the Lake Ontario basin.; I found low and variable survival rates of Atlantic salmon embryos, with an average of 29.4% ± 26.7% (SD) to the eyed developmental stage and only 2.2% ± 6.5% to emergence. However, these survival rates suggest that the incubation period is not an absolute limiting factor for the restoration of Atlantic salmon. The survival rates were not correlated to gravel quality indices (percent of fines <2 mm, geometric mean and the fredel index), substrate permeability, or intragravel dissolved-oxygen concentrations.; Using these survival rates and intragravel parameters and a sensitivity analysis, I discovered that the SIDO model produced unrealistic predictions of these parameters. The correlations between the intrusion of fine sediments, intragravel water velocity, dissolved-oxygen concentrations and survival of the embryos were not found in most of the predictions produced by the SIDO model.; During underwater observations conducted to quantify habitat utilization and interspecific competition, I recorded vertical segregation in the water column between salmonid species but habitat segregation according to water depth and velocity was less pronounced. Atlantic salmon hold better feeding positions by moving closer to the area of greater water velocity which carries more food when the number of trout was reduced. Laboratory experiments on the effects of interspecific competition on growth rates provided further evidence that rainbow trout are more aggressive than Atlantic salmon.; The 3 components of this thesis (embryos' survival, SIDO model and interspecific competition) provide not only a better understanding of the feasibility of Atlantic salmon restoration but also lead to future research design.