5. LAKE EUTROPHICATION AND PRODUCTIV 



Fishery Deterioration in the Great Lakes 



Before human settlement, the wa- 

 ters of the Great Lakes abounded in 

 fish characteristic of large lakes with 

 cold, clear water. But the fish popu- 

 lations and the environment of the 

 Great Lakes have undergone pro- 

 gressive deterioration for more than 

 a century. Degradation has acceler- 

 ated at an alarming rate in recent 

 years. Valuable fish such as Atlantic 

 salmon, lake trout, whitefish, blue 

 pike, and walleye comprised 80 to 

 90 percent of the production of the 

 early fishery; but in recent years 

 these species have contributed less 

 than 5 percent of the catch from the 

 lakes in which they are still present. 

 (See Figure VIII-14) 



The Great Lakes, 64 percent of 

 which lie within U.S. boundaries, 

 cover 95,000 square miles and are 

 the largest and most valuable fresh- 

 water resource in the world. The 

 fish populations constitute the great- 

 est and most valuable renewable re- 

 source of the lakes. Peak U.S. fishery 

 production occurred around 1900, 

 when 100 to 120 million pounds of 

 mostly high-value species were taken 

 annually. The catch subsequently de- 

 clined. In 1963, it reached a low of 

 less than 53 million pounds — com- 

 posed primarily of medium- and low- 

 value species (alewives, carp, chubs, 

 perch, sheepshead, smelt, and suck- 

 ers). 



Causative Factors 



Until recently, the causative fac- 

 tors of this drastic change have been 

 a subject of great controversy. It is 

 now known that modifications of the 

 drainage by agriculture, urbanization, 

 and industrialization, and intensive, 

 selective fishing for the most valuable 

 species have caused major changes 

 that led to invasions of new species 

 and deterioration of water quality. 



The exact ways in which these in- 

 fluences have affected individual spe- 

 cies or groups of species are not yet 

 completely understood. Careful re- 

 view of the entire sequence of events 

 within the Great Lakes and their 

 drainage, however, is providing in- 

 formation essential to the formula- 

 tion of environmental criteria and 

 elaboration of management plans 

 that can be implemented to reverse 

 undesirable trends and restore much 

 of the value of the Great Lakes and 

 their fisheries. 



Settlement of the Lake Ontario 

 basin and the construction of the 

 Erie and Welland canals were the 

 events that initiated a chain reaction 

 that has now upset the ecological 



balance of fish populations through- 

 out the Great Lakes. As noted, Lake 

 Ontario and the St. Lawrence River 

 were once inhabited by an abundance 

 of cold-water species dominated by 

 the Atlantic salmon. Early accounts 

 describe how the cutting of the for- 

 ests and agricultural development 

 increased water temperatures and 

 lowered flows of streams in which 

 Atlantic salmon spawned. Mill dams 

 blocked spawning streams. Disposal 

 of mill wastes in streams, as well 

 as intensive fishing, also contributed 

 to a sharp decline of Atlantic salmon 

 during the mid-1800's. 



The salmon were scarce by 1880 

 and extinct by 1900. Repeated at- 

 tempts to re-establish them have 



Figure VIII-14 — COMMERCIAL FISH CATCH: LAKE MICHIGAN 



100 



60 



O 

 o 



40 - 



O 30 



1898- 1910- 

 1909 1919 



1920- 1930- 1935- 1940- 1945- 1950- 1955- 1960 1961 1962 1963 1964 1965 1966 

 1929 1934 1939 1944 1949 1954 1959 



The diagram shows statistics of the commercial fish catch on Lake Michigan 

 from 1898 to 1966. The degradation of the fish population is clearly evident; 

 although the total catch returned to turn-of-the-century levels in 1966, almost all 

 of it consisted of alewives and other low-value species. 



261 



