ENRICHMENT AND INVASION (1900-1950) 



The stage was set and the signs were present in 1900 for what was to 

 follow. Changes in the biological, chemical, and physical environment of 

 the Great Lakes became the rule and not the exception. The records of 

 these changes, unfortunately, are incomplete, often inaccurate, and, for 

 the fish populations, often not a true representation of species abundance. 

 The analysis of changes in the abundance of species until recently was 

 based on the reported catch of commercial fishermen. High prices often 

 maintained high catches in the face of a decreasing abundance. Conversely, 

 low production often was due to low prices and lack of demand for a species 

 rather than low population levels. Despite these handicaps, the changing 

 conditions often became too obvious to be ignored. 



Changes in fish-species composition, losses and gains, differ in time 

 between the lakes, but the sequence of species change often was similar 

 (Smith, unpublished manuscript). In general, the species that declined 

 were those most sought after by the commercial fishery. A few significant 

 exceptions exist to this generalization, and it is the exceptions which 

 clearly indicate stresses other than fishing on the biological communities 

 of the Great Lakes. 



Changes which occurred in native fish species of commercial interest 

 between 1900 and 1971 are summarized in Table 4. Detailed discussion of 

 these declines by species and lakes appear in Smith (1968), the papers of 

 the SCOL Symposium (1972), and Christie (1974). The data presented in 

 Table 4 refer to production trends in the total lake and, therefore, are 

 not descriptive of events in the unique ecological areas of each lake such 

 as the Bay of Quinte in Lake Ontario, the western basin of Lake Erie, 

 Saginaw Bay of Lake Huron, or Green Bay of Lake Michigan (Figure 1). These 

 geographic areas were, and are, more shallow and productive and warmer than 

 the open portions of the lake to which they are connected. The fish-species 

 complex here was also more diverse than in the open lake, containing many 

 warmwater species, especially the centrarchids and percids. 



Ecological and Cultural Changes, 1900-1925 



During the first quarter of the 20th century, the northern pike fishery 

 was reduced to a fraction of former production; lake whitefish in Lake 

 Ontario and lake herring in Lake Erie began declining; the first sea 

 lamprey was reported in Lake Erie; and the first rainbow smelt were found 

 in Lakes Michigan and Huron. The gains and losses in these and other 

 species were to be repeated many times in the next 50 years in the other 

 lakes. 



The introduction of the smelt into Crystal Lake in the drainage basin 

 of Lake Michigan was deliberate, but its establishment in Lake Michigan was 

 not contemplated, nor was its rapid spread to other Great Lakes. The sea 

 lamprey reached Lake Erie nearly 100 years after the Wei land Canal was 

 opened and established itself in the upper lakes. The beginning of the 

 declines in lake whitefish and lake herring were, of course, undetected at 

 the time and thus alarmed no one. 



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