Lake Ontario: Effects of Exploitation, Introductions, and Eutrophication on the Salmonid Community

Abstract

Commercial catch statistics were analyzed to follow the sequence of events in the deterioration of the major fish stocks of Lake Ontario. Atlantic salmon (Salmo salas), lake trout (Salvelinus namaycush), burbot (Lota lota), deepwater ciscoes (Coregonus sp.), and whitefish (Coregonus clupeaformis) have all disappeared or declined seriously in abundance. Only the colonists alewife (Alosa pseudoharengus), smelt (Osmerus mordax) and white perch (Morone americana) are currently abundant. Abundance of deepwater ciscoes is thought to have been controlled originally by the piscivores lake trout and burbot. Three deepwater cisco species are inferred to have been progressively eliminated by overfishing, leaving only the smallest and least valuable present when the fishery collapsed. The effects of the sea lamprey (Petromyzon marinus) on the Lake Ontario fishes are held to have increased with the reduction of the number of dams in the watershed, and as fishing reduced numerical abundance and average size of the prey fishes. The early colonists alewife and carp (Cyprinus carpio) were thought to have stabilized early. It was suggested smelt were suppressed for many years by trout and burbot predation, and after the release of this constraint, the smelt in turn caused the collapse of the deepwater ciscoes and other species through predation. The white perch invasion of the Bay of Quinte was thought particularly swift and successful because of the absence of predators. Yellow perch (Perca flavescens) abundance may have increased because of eutrophication effects in the nearshore areas. Recent deterioration of water quality appears so extreme as to ensure that the last premium species which used the inshore areas cannot return. Overfishing is thought to have been the major destabilizing influence. The role of the open lake predators in the vectoring of energy and materials through the system is discussed.