Assessing the Potential Effects of Water Level Regulation on Lake Trout in Northern Canadian Lakes

Lakes in northern Canada tend to be low in diversity with lake trout as the top predator suggesting that lake trout play a major role in ecosystem function and productivity. Protecting lake trout in northern lakes from the negative effects of activities involving water level regulation is a major goal of management agencies although achievement of this goal is hampered by a lack of information on spawning depth. We used an empirical relationship between spawning depth and lake area to develop first order estimates of the effects of water level fluctuations on spawning success for several different categories of lake size in the Northwest Territories (Canada). As a means of developing more precise estimates of spawning depth within individual lakes, we evaluated a protocol for converting detailed observations of potential spawning habitat and its use into a spawning habitat use curve. From this analysis it was evident that for a given water level fluctuation, lake trout in smaller lakes are more at risk and that these are the predominant size of lake in the Northwest Territories. The use of the spawning habitat use curve provided an effective means for assessing the effects of small scale changes in water level, and can readily take account information on winter ice cover, and lead to a better understanding of limitations to habitat use in lakes throughout the Northwest Territories.