Bay populations of walleye and whitefish. In Lake Erie the sauger produc- 

 tion fell below 0.5 million pounds in 1946 (Baldwin and Saalfeld, 1962) for 

 the first time after nearly 70 years of production between 1 and 6 million 

 pounds. Environmental changes, plus heavy exploitation, were believed to 

 be the causes (Table 7) . 



The decline of the lake herring, historically the most productive 

 species in the Great Lakes (Smith, 1968), began in Lake Erie in 1925, and 

 by 1963 this fish had become commercially extinct in all the lakes except 

 Superior. Heavy exploitation was undoubtedly a factor in the decline of 

 the lake herring. The role and impact on this decline of introduced ale- 

 wife and smelt and of environmental factors, however, have not been iso- 

 lated. The collapse of the lake herring stocks in the mid-1920's was the 

 event most responsible for stimulating interest and concern in the welfare 

 of the Great Lakes aquatic environment. This concern was primarily res- 

 ponsible for identifying the rapid deterioration in the water quality of 

 Lake Erie, which is discussed in a following section. 



Water Quality and Population Changes, 1925-1950 



Changes in dissolved chemical constituents continued to accelerate 

 after 1925 in all the lakes except Superior (Table 8). The absolute values 

 of these "indicator" chemical parameters are of no toxicological concern, 

 but again the rate of change indicated substantial inputs from cultural and 

 industrial sources. Concentrations of these and other chemical compounds 

 must have been substantial in the receiving waters near the pollution 

 source. The loss of whitefish, lake herring, sauger, and other species 

 from the inner portions of Saginaw and Green Bays due to water quality 

 changes would be expected. 



TABLE 8. ESTIMATED AVERAGE CONCENTRATIONS OF DISSOLVED CHEMICAL 



CONSTITUENTS IN THE GREAT LAKES (EXPRESSED IN MG/LITER) a 



From Beeton, 1969. 



210 



