SECTION 18 

 HISTORY OF CHANGES IN FISH SPECIES OF THE GREAT LAKES 



John F. Carr 



INTRODUCTION 



Changes began in the fish-species complex in the Laurentian Great Lakes 

 almost immediately after the first permanent settlers arrived in the basin 

 in the early 1800's. Changes occurred slowly at first, but accelerated 

 with the increased activities of man. These changes continue today and 

 will continue in all probability for decades or even centuries because 

 man's manipulations of the environment are continuing. 



The Great Lakes are young; only about 10,000 years have passed since 

 the melting of the glaciers. Youthful lakes such as these are generally 

 characterized by low biological productivity, low nutrient content, and 

 high transparency; they are often deep and cold. So are the Laurentian 

 Great Lakes even today. With the exception of a few areas, the waters of 

 the Great Lakes are of excellent quality and can be used as potable water 

 without treatment. Yet man's impact on these lakes, especially on the fish 

 populations, has been so drastic that the Laurentian Great Lakes have been 

 used as worldwide symbols of accelerated aging. Some scientists have esti- 

 mated that the lakes, especially Erie and Ontario, have aged more in the 

 past 150 years than in the preceding 10,000 years. That changes of this 

 magnitude could occur in lakes as large as the Great Lakes was not 

 considered possible only a few years ago. Today, however, we are beginning 

 to realize the tremendous capacity we possess to change (usually to our 

 detriment) even the oceans and the atmosphere. 



The purpose of this paper is to discuss the changes which have taken 

 place in the fish populations of the Great Lakes and the stresses which 

 have caused these changes. It has become obvious that many of the causes 

 of the declines are the results of deliberate actions rather than subtle un- 

 predictable factors. 



The stresses which have been placed on the fish communities of the 

 Great Lakes have been sequential and reflect the progress of man's occupa- 

 tion of the basin and his technological development. The most obvious and 

 primary direct stress has been the intensive and selective exploitation of 

 the fish stocks. This stress began early in the 19th century and continues 

 to some degree today. Environmental stresses have not been as direct or as 

 obvious, but were present as early as 1830 and have been additive as well 



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