several years of research and testing thousands of chemicals, one was found 

 which was toxic to the lamprey but not lethal to other fish. Treatment of 

 lamprey-infested streams with the chemical 3-trif luoromethyl-4-nitrophenol 

 (TFM) began in 1958. By 1962, 2 years after all known lamprey nursery 

 streams had been treated in Lake Superior, success was verified when the 

 number of adult lampreys at assessment barriers was reduced nearly 85% 

 (Baldwin, 1964). The incidence of lamprey wounds on lake trout dropped 

 sharply, and survival of lake trout increased dramatically in Lake Superior, 

 A method of control had been found just in time to save the last natural 

 population of lake trout in the Great Lakes. The first complete treatment 

 of all Lake Michigan lamprey- infested streams was completed in 1963, Lake 

 Huron in 1970, and Lake Ontario in 1972. Chemical treatment of streams at 

 intervals of 2-4 years must continue, however, if the rehabilitation of 

 lake trout and other species is to become permanent. 



The introduction of Pacific salmon in the Great Lakes had been 

 attempted many times, but had produced limited results until the successful 

 introduction of the coho salmon ( Oncorhynchus kisutch ) in Lake Michigan in 

 1966. By 1969 coho and chinook salmon ( Oncorhynchus tshawytscha ) had been 

 introduced into all the upper lakes. The purpose of stocking coho and 

 chinook salmon in the Great Lakes was to increase the sport fishing 

 potential and not to establish self-sustaining populations. "Successful" 

 introduction, therefore, relates to rapid growth and high survival rates. 

 The pink salmon ( Oncorhynchus gorbuscha ), however, was an "unplanned" plant 

 in Lake Superior, where it succeeded in establishing spawning runs in 1959 

 and by 1975 had become established in Lakes Huron and Michigan. 



Supplemental plantings of lake trout, following lamprey control, have 

 been made since 1958 in Lake Superior. The stocks have been built up to 

 near pre-lamprey levels. Reproduction of hatchery-reared fish has been dis- 

 appointing, however. Only in the last 2 or 3 years has the outlook im- 

 proved, when increasing numbers of young native trout have been reported. 



The re introduction of lake trout in Lake Michigan, beginning in 1965, 

 has proved extremely successful in terms of survival and growth. No evi- 

 dence of reproduction, however, has been reported. Lake trout are now 

 being stocked in Lakes Huron and Ontario. Biologists continue to be 

 optimistic about the reestablishment of self-sustaining populations of lake 

 trout in all the Great Lakes, except Erie. 



Salmonids other than lake trout and Pacific salmon have been stocked in 

 the Great Lakes since the lamprey has been controlled. Steelhead trout 

 (rainbow trout), brown trout, brook trout, and Atlantic salmon are now 

 stocked in the lakes. Over 20 million salmonids annually are stocked in 

 the Great Lakes. In 1974 the first experimental plant of hatchery-reared 

 saugers was stocked in Lake Erie. 



Environmental Changes, 1950-1975 



Scientific investigations of environmental conditions of the Great 

 Lakes have increased exponentially during the past 25 years. Changes in 

 fish populations, benthic organisms, plankton, and water quality are now 



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