ductivity of fish populations, the increase in mortality was clearly the 

 most sensitive and meaningful observation of effect measured in the study. 



CONCLUSIONS 



The significant increase in mortality of lake trout fry during 6 months 

 of exposure to levels of DDE and PCBs in food and water similar to those in 

 Lake Michigan strongly suggests that these chlorinated hydrocarbons are a 

 limiting factor in the reproduction of lake trout in the lake. Whether 

 these two contaminants are the sole or even major cause for reproductive 

 failure of the lake trout is unclear. Other factors such as the presence 

 of exotic species and the spawning behavior of planted fish undoubtedly play 

 a role. The known presence, however, of additional chlorinated hydrocarbons 

 such as dieldrin, chlordane, and chlorinated camphenes, as well as of 

 several other organic and inorganic contaminants in the water and biota of 

 the lakes, raises serious questions about the potential additive or syner- 

 gistic effects of these multiple contaminants. Regardless of the ultimate 

 answer to these questions, the current levels of PCBs and DDE in the lake 

 appear sufficient to impede the restoration of self-sustaining populations 

 of lake trout in Lake Michigan. 



ACKNOWLEDGEMENTS 



The studies and conclusions reported here resulted from the dedicated 

 and professional effort of the entire staff of the Section of Physiology 

 and Contaminant Chemistry, Great Lakes Fishery Laboratory, Special credit 

 goes to Robert E. Reinert for initially identifying chlorinated hydrocarbons 

 as a potential problem in Lake Michigan and for directing the early studies 

 on hatchability of lake trout eggs. Principal investigators in the studies 

 I discussed were William H. Berlin, Roger A. Bergstedt, Robert J. 

 Hesselberg, Michael J. Mac, Dora R. May Passino, and Donald V. Rottiers. 

 The assistance of Lawrence W. Nicholson and James R. Olson in providing 

 chemical analyses for most of the studies, and of Neal R. Foster and Thomas 

 L. Baucom in editing this report is gratefully acknowledged. 



REFERENCES 



Burdick, G.E., E.J. Harris, H.J. Dean, T.M. Walker, J. Skea, and D. Colby. 

 1964. The accumulation of DDT in lake trout and the effect on repro- 

 duction. Trans. Am. Fish. Soc. 93(2): 127-136. 



Great Lakes Fishery Laboratory. 1974. Great Lakes Fishery Program. D]_ 

 Sport Fishery and Wildlife Research 1972, pp. 22-32, U.S. Department 

 of the Interior, Bureau of Sport Fisheries and Wildlife. 124 pp. 



Great Lakes Fishery Laboratory. 1978. Great Lakes Fisheries. ln_ Sport 

 Fishery and Wildlife Research 1975-76, pp. 46-57, U.S. Fish and 

 Wildlife Service. 140 pp. 



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