SECTION 6 



CHLORINATED HYDROCARBONS AS A LIMITING FACTOR IN THE 

 REPRODUCTION OF LAKE TROUT IN LAKE MICHIGAN^ 



Wayne A. Willford^ 



THE FISHERY 



From about 1890 until 1945, the lake trout ( Salvelinus namaycush ) was 

 the most valuable and sought-after commercial species in Lake Michigan. The 

 annual commercial catch averaged 8.2 million pounds (3,700 metric tons [t]) 

 from 1890 to 1911, 7.0 million pounds (3,200 t) from 1912 to 1926, and 5.3 

 million pounds (2,400 t) from 1927 to 1939. The catch increased slightly to 

 an annual average of 6.6 million pounds (3,000 t) during 1940 to 1944, but 

 then began to decline precipitously in 1945 and had fallen to only 342,000 

 pounds (155 t) by 1949 (Figure 1). In 1954, the catch was a mere 34 pounds 

 (15 kg), and by 1956 the species was probably extinct in Lake Michigan 

 (Wells and McLain 1973). 



The gradual decline in the commercial harvest of lake trout from 1893 to 

 1938 is believed to have resulted from excessive exploitation (Van Oosten 

 1949; Wells and McLain 1973). Although the commercial harvest of lake trout 

 continued into the early 1950's, the apparent extinction of the species in 

 about 1956 is believed to have been caused directly by the predatory sea 

 lamprey ( Petromyzon marinus ), an exotic species that became firmly estab- 

 lished in Lake Michigan in the decade following its first reported presence 

 there in 1936 (Wells and McLain 1973). 



Early attempts to control the sea lamprey consisted of installing elec- 

 trical and mechanical barriers, which blocked the spawning runs of adults. 

 Between 1953 and 1958, barriers were constructed across 65 tributaries 

 flowing into Lake Michigan. At about the same time (in the late 1950's) a 

 successful lampricide, 3-trif luoromethyl-4-nitrophenol (TFM), was discovered 

 and developed by scientists at the Hammond Bay Biological Station of the 

 U.S. Fish and Wildlife Service (USFWS). This compound was soon being used 

 to kill larval sea lampreys (ammocoetes) in tributary streams before they 

 could metamorphose and migrate downstream into the lake. Most barrier 

 operations were discontinued in 1960 in favor of TFM treatments, thus set- 



^Contribution 545, Great Lakes Fishery Laboratory. 



^U.S. Fish and Wildlife Service, Great Lakes Fishery Laboratory, 1451 Green 

 Road, Ann Arbor, Michigan 48105. 



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