Consumption of Fish and Other Prey Items by Lake Erie Waterbirds

Abstract

Lake Erie provides valuable habitat for large populations of waterbirds that rely on fish and other aquatic biota for food. To better understand the relationship between waterbirds and their prey, it is important to quantify the role of waterbirds in the food web. Field observations of their population sizes and diet preferences were applied to a bioenergetics model to estimate consumption of fish and other items by waterbird species occupying the three basins of Lake Erie in the late 1990s. The total quantity of fishes consumed annually by resident and migrating birds on Lake Erie was 18,776 metric tons. Fish consumption by nesting and migrant waterbirds was greatest in the western basin of Lake Erie (14,784 metric tons/yr) followed by the eastern (2,078 metric tons/yr) and central (1,914 metric tons/yr) basins. Migrant populations of red-breasted mergansers consumed the most fish (6,612 metric tons/yr). These diving ducks consumed approximately 35% of the total amount of fish consumed by waterbirds on the lake. Nesting populations of double-crested cormorants (5,857 metric tons/yr), nesting populations of herring gulls (1,597 metric tons/yr), and migrant common mergansers (1,149 metric tons/yr), were the second, third, and fourth largest consumers of fish from Lake Erie, respectively. Waterbirds consume approximately four times more fish by weight than were harvested by Ontario's commercial fishery in 2000; however, in general, the species of fishes most often consumed by waterbirds are not of economic importance. However, there may be exceptions to this rule.