Changes in the North Channel fish community, with emphasis on pink salmon (Oncorhynchus gorbuscha Walhaum)

Abstract

Historical trends in commercial fishery yields were examined for evidence of structural changes in the North Channel fish community. Significant declines in the abundance of indigenous species occurred primarily as a result of man’s activities. Lake sturgeon (Acipenser fulvescens Rafinesque) were harvested down to low levels by 1900. Introductions of exotics to the fish community were associated with major changes. Rainbow smelt (Osmerus mordax Mitchill) and sea lamprey (Petromyzon marinus Linnaeus) colonized the channel in the late 1930s. Concurrently, lake trout (Salvelinus namaycush Walbaum) and burbot (Lota lota Linnaeus), the top deepwater predators, declined to near extinction. Lake whitefish (Coregonus clupeaformis Mitchill) and shallow-water cisco (Coregonus artedii Lesueur) also declined. Without predation pressure, smelt abundance increased to high levels in the 1950s and alewife (Alosa pseudoharengus Wilson), another exotic, peaked during the 1960s. Both species equilibrated at lower levels in the 1970s, perhaps favouring colonization by pink salmon (Oncorhynchus gorbuscha Walbaum). Pink salmon which are larger and more fecund in Lake Huron than in Lake Superior, are increasing rapidly in numbers and are expanding their range in the channel. Certain whitefish stocks have increased sufficiently to support fishery yields greater than those of the 1930s, despite considerable exploitation pressure. This success is partially in response to the control of sea lamprey since 1961. However both lake whitefish and walleye (Stizostedion vitreum Mitchill) are now rare in the east end of the channel, possibly due to environmental factors such as acid precipiation and metal contaminants. Community stability will not likely be attained until a suitable climax predator becomes reestablished.