Abundance and prey demand of Common Loon (Gavia immer ), Lake Opeongo, Algonquin Provincial Park

Estimation of predator abundance is important for understanding prey demand in aquatic food webs. This thesis investigated the detectability of Common Loons (Gavia immer) using distance sampling protocol to accurately estimate density on a large breeding lake on the Canadian Shield. Results show that the assumption of perfect detection was not met for loons on the lake environment and that detectability varied as a function observer skill and group size. Distance sampling yielded density estimates for the three most abundant avian piscivores: Common Loon, Herring Gull ( Larus argentatus), and Double-crested Cormorant ( Phalacrocorax auritus). Estimated food requirements, combined with species density estimates, were used to predict the prey demand by each avian population. A mean annual fish production of 6 kg ha-1 (80%CI=216 kg·ha-1) was estimated based on a model which links phosphorus concentration to lake production. Estimated annual avian consumption (7.5kg·ha-1; 90%CI=5.7-9.9kg·ha-1) exceeded the mean and lower prediction limits for fish production. Avian piscivores consumed 48% of annual fish production, based on the upper prediction. Estimated consumption by loons, the most abundant piscivore, accounted for at least 39% of fish production. Results were used to make recommendations for future surveys of loons on large lake ecosystems.;Key words: Distance Sampling, Detection Probability, g(0) assumption, Density Estimates, Common Loon, Daily Food Requirements, Seasonal Prey Demand, Fish Production, Algonquin Provincial Park.