PROGRESS IN BIOLOGICAL INQUIRIES, 1931 469 



St. Clair is plankton poor and that there is no opportunity for 

 production in the river itself. 



In the open lal^e the principal bottom organism was the mayfly, 

 Hexagenia. Near the mouths of the rivers this form was replaced 

 by tubiticid worms, which are recognized as highly tolerant to pollu- 

 tion. Using the number of worms as a criterion, the polluted area 

 was divided into zones of heavy, moderate, and light pollution. 

 Heavy pollution was found only at the mouths of Maumee and Raisin 

 Rivers, and the total area involved was roughly 10 square miles. 

 Moderate pollution was found also at the mouth of Detroit River; 

 the combined area for the three rivers was approximately 20 square 

 miles. Because of the accumulations of decaying organic matter 

 in these two areas of heavy and moderate pollution, they can not be 

 considered highly suitable for spawning grounds of fish. The com- 

 bined area of the zones of light pollution was roughly 75 square miles. 

 It is believed that the major part of this zone includes a substratum 

 suitable for spawning purposes. 



The undesirable effects of pollution have been contamination of 

 the water by sewage bacteria and the reduction of spawning areas, 

 but the harm done to the commercial fisheries by reduction of spawn- 

 ing areas has no doubt been offset, at least in part if not entirely, by 

 the increase in plankton, which serves as food for young fish and 

 for the adults of plankton-feeding species. 



LAKE CHAMPLAIN 



The chief objective of the Lake Champlain investigation was to 

 determine the effect of commercial seining in Missisquoi Bay by 

 Canadian residents on the abundance of pike-perch in the United 

 States waters of the lake. It was believed that the series of public 

 hearings held by the International Fact-finding Commission at 

 Plattsburg, N. Y., Swan ton, Vt., and Phillipsburg, Quebec, on Oc- 

 tober 15, 16, and 17, respectively, would complete the field work; 

 but after a conference at Phillipsburg, Quebec, of the State and 

 Provincial officials involved, it was found necessary to collect addi- 

 tional data, with special reference to sexual maturity of yellow pike- 

 perch and the abundance of whitefish in Vermont waters. In co- 

 operation with the State of Vermont, Doctor Van Oosten carried on 

 the necessary seining experiments at Larrabees Landing and its 

 vicinity during the period October 26 to November 16, 1931. Most 

 of the data collected previously during this investigation have been 

 analyzed in the laboratory; and as soon as other duties permit, the 

 final report with recommendations will be submitted by the 

 commission. 



WISCONSIN LAKE STUDIES 

 STUDIES OF FISH GROWTH 



The investigations of the lakes of northeastern Wisconsin which 

 the bureau conducted in cooperation with the Wisconsin Geological 

 and Natural History Survey in 1927, 1928, and 1930 were continued 

 through 1931. During the months of July, August, and early Sep- 

 tember Dr. Ralph Hile, of the bureau, and Edward Schneberger, of 



