LAKE EUTROPHICATICN AND PRODUCTIVITY 



lation of lake trout and to the abun- 

 dance of other large native species ■ — 

 whitefish, lake herring, and larger 

 deep-water ciscoes — as well as to 

 the recently introduced coho and 

 chinook salmon. 



In summary, the invasion of ma- 

 rine species made possible by eco- 

 logical disruption during settlement 

 of the Lake Ontario basin in the 

 1800's has been a major contributing 

 factor to substantial reduction of the 

 fishery productivity of Lakes On- 

 tario, Huron, and Michigan, and the 

 ultimate effects on Lake Superior are 

 still uncertain. 



Effects of Deteriorating Water 

 Quality — The most serious threat 

 to the biological stability and fishery 

 productivity of the Great Lakes has 

 been a progressive deterioration of 

 water quality. During early settle- 

 ment within the Great Lakes drain- 

 age, organic pollution characteristic 

 of nonindustrialized society fouled 

 tributaries of the Great Lakes; it had 

 virtually eliminated populations of 

 river-run lake trout, whitefish, lake 

 herring, walleye, yellow perch, and 

 sturgeon by the late 1800's and early 

 1900's. These populations made up 

 a major segment of the total fish 

 stocks in the lakes and they have 

 never recovered. 



More recently, there has been in- 

 creasing evidence that a much more 

 ominous type of pollution has ac- 

 companied advanced industrializa- 

 tion. This "new" pollution consists 

 of discharges of complex chemical 

 and physical wastes from advanced 

 industrial, agricultural, and urban ac- 

 tivities, and from massive releases 

 of heated waste water from industries 

 and power-generating plants. 



The combined effects of the "con- 

 ventional" and "new" environmental 

 contaminants cannot be described or 

 their influences on aquatic life ex- 

 plained by existing criteria or meth- 

 ods. The mechanisms of their in- 

 fluence on aquatic life are unknown, 

 but the fact that they have had major 



detrimental effects on aquatic life is 

 beyond question. 



Southern Green Bay, Saginaw Bay, 

 Lake St. Clair, the Detroit River, and 

 all of Lakes Erie and Ontario are 

 polluted to the extent that they have 

 lost virtually all of the "clean water" 

 species that were once abundant in 

 them. The sequence in which fish 

 declined or disappeared and water 

 quality deteriorated has been the 

 same in all areas. The lake trout 

 declined first, followed by lake her- 

 ring, whitefish, sauger, blue pike, 

 walleye, and yellow perch. The deep- 

 water ciscoes are very sensitive to 

 environmental degradation, but they 

 decline late in the sequence because 

 the deep waters are influenced later 

 than shallow areas by contamination. 



Lakes Erie and Ontario have been 

 the most seriously affected by pol- 

 lution. These were the two most 

 productive Great Lakes. The species 

 of fish characteristic of large northern 

 lakes were once extremely abundant 

 in both lakes, but all are now greatly 

 reduced, rare, or extinct. 



Since Lake Erie was not influenced 

 greatly by the invasions of the alewife 

 and sea lamprey, the loss of its valu- 

 able species can be attributed pri- 

 marily to the complex, yet poorly 

 understood, effects on aquatic life 

 of massive introductions of biological, 

 chemical, and physical wastes of an 

 advanced industrialized society. Lake 

 Erie still has large populations of 

 fish. Sheepshead, carp, and goldfish, 

 which have little present value or 

 use, abound in the lake and its bays. 

 Present biological information shows, 

 however, that populations of the 

 more valuable walleye, yellow perch, 

 and smelt appear to be in imminent 

 danger of collapse. Fishery produc- 

 tivity of the large central basin of 

 Lake Erie has been reduced greatly 

 in recent years by oxygen depletion 

 in the bottom waters, which has made 

 a major portion of the lake uninhabit- 

 able by fish or fish-food organisms. 



The fish populations of Lake On- 

 tario have been affected more se- 



riously than any other Kike. Early 

 reductions of fish stocks due to in- 

 fluences of the alewife and sea lam- 

 prey have been compounded in recent 

 years by additional reductions caused 

 by the extreme deterioration of water 

 quality in Lake Ontario, which is 

 the ultimate recipient of all wastes 

 entering both Lakes Erie and On- 

 tario. The vast deep-water region of 

 Lake Ontario is devoid of any valu- 

 able and abundant species of fish. 

 The native species that supported the 

 most productive and prosperous fish- 

 eries of the Great Lakes during the 

 early and mid-lSOO's have all become 

 greatly reduced or rare; many are 

 extinct. 



The native species lost in Lake 

 Ontario due to water-quality degra- 

 dation — lake trout, whitefish, lake 

 herring, deep-water ciscoes, deep- 

 water sculpin — are the only kinds 

 of fish that thrive in any of the large, 

 deep lakes of the world. If the water 

 quality of Lake Ontario cannot be 

 restored so that it is again favorable 

 for these species, the lake's fishery 

 potential will be lost forever. If the 

 water quality of the other deep 

 lakes — Michigan, Huron, and Supe- 

 rior — continues to deteriorate, their 

 vast deep-water regions will also 

 become fishery deserts. 



Status of the 

 Environmental Science 



Development of an understanding 

 of the precise causes of the biological 

 degradation of the Great Lakes is in 

 the formative stages, and is advanc- 

 ing slowly in a few scattered problem 

 areas. Existing techniques and gen- 

 eral knowledge of present and poten- 

 tial problems seem adequate to for- 

 mulate a systems approach that 

 could, when sufficient monitoring and 

 research information become avail- 

 able, describe and predict the biologi- 

 cal interactions in the Great Lakes 

 environment and relate biological re- 

 sponses to activities of man in the 

 lake basins. 



263 



