Lake Superior: Effects of Exploitation and Introductions on the Salmonid Community

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Abstract
Lake Superior is highly oligotrophic and not very productive. It has not, however, been much affected by man's activities. Substantial quantities of woody allochthonous materials entered the lower reaches of tributaries and their estuaries from the pioneer lumbering industry. These undoubtedly depreciated the shallow-water benthic environment and may have adversely affected fish stocks in the immediate areas concerned, especially those of lake sturgeon (Acipenser fulvescens) and lake whitefish (Coregonus clupeaformis). At present, local areas of urban or industrial pollution can be identified but, in general, appear to have had little adverse effect on fish stocks, although the collapse of one walleye stock has been attributed to pollution from a paper mill. Every commercial species has, however, been severely depleted. Recent declines can be correlated with predation by sea lamprey (Petromyzon marinus) but, without exception, all species give evidence of extensive overfishing long before sea lamprey entered the lake. That this has not been more obvious is due to the stratification of catch statistics by arbitrary geographic areas (statistical districts) which are too large to relate meaningfully to either fish distributions or patterns of fishery operations. Because fish are generally distributed as local, often small, quasi-discrete stocks, they were exploited sequentially by the young, developing fishery. In this way stock after stock was depleted while conventional yield statistics gave an impression of relative stability. The lag before these statistics indicated the decline appears to be related to the degree of dispersal characteristic of each species. Thus the decline of the sturgeon was first evident, that of the lake trout (Salvelinus namaycush) last. Recovery has been slight but modern hatchery technology clearly provides a prospect for rejuvenating existing stocks or developing new ones. In either case, such synthetic populations will offer favorable opportunities for detailed investigation of the nature of fish distribution and its bearing on the interpretation of catch statistics.

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