470 U. S. BUREAU OF FISHEEIES 



the Wisconsin survey, with the aid of two assistants, collected data 

 for growth study from 7,764 fish. These collections were made from 

 six " type " lakes in which the growth rates of the perch, rock bass, 

 and Cisco are being studied. The policy of distributing scale en- 

 velopes to sport fishermen for the purpose of obtaining data on the 

 game fish of the region was continued. 



Since preliminary study indicated the possible existence of dis- 

 tinct races of ciscoes in the different lakes, a total of 720 specimens 

 from five lakes were preserved for purposes of morphometric study. 



The question of the existence within a single lake of local races 

 having different growth rates was attacked from two angles. In 

 Muskellunge Lake, which has a rather complex basin, collections of 

 scale material were made in two widely separated bays. In the same 

 localities 1,400 rock bass, bluegills, and perch were tagged. Since 

 the tagging operations were conducted late in the season, the re- 

 coveries were not numerous. It is hoped that later recoveries may 

 lead to conclusive results on the question of the extent of the wander- 

 ings of these species within the lake. 



COOPERATIVE UMNOLOGICAL INVESTIGATIONS 



Physical, chemical, and biological studies of several of the lakes 

 of northeastern Wisconsin were continued in the summer of 1931. 

 The Trout Lake Laboratory of the Wisconsin Geological and Nat- 

 ural History Survey was opened on June 28 and the investigations 

 continued until September 10; the fish work extended to September 

 18. These studies are entirely supervised and largely financed by the 

 survey; but, in recognition of the bureau's modest cooperation, the 

 following report is submitted by Prof. Chancey Juday and, because 

 of its interest in relation to hydrobiological and aquicultural research 

 in which the bureau is engaged, is published here. 



The field party consisted of E. A. Birge, C. Juday, Edward Schneberger, F. H. 

 Couey, S. X. Cross, George E. Burdick, J. B. Goldsmith, H. C. Baum, and K. A. 

 Siler, biologists ; F. L. Taylor, chemist ; and W. L. Hafner, part-time surveyor 

 and cartographer. In addition, Leslie Titus was employed in making chemical 

 analyses of the lake residues in the chemical laboratory of the University of 

 Wisconsin during the summer. The staff of the Bureau of Fisheries that took 

 part in these cooperative investigations consisted of R. O. Hile, H. M. Field, 

 and William Duden. 



With the exception of the work on the transmission of solar energy by these 

 lake waters, the investigations were confined chiefly to the six lakes that 

 were selected for an intensive study of their fish fauna. Observations on solar- 

 energy transmission were made on a number of other lakes, representing vari- 

 ous types, in addition to those that were made on the six lakes selected for the 

 fish studies. 



A more sensitive reading instrument was used during the summer of 1931 

 for the oliservations on solar-energy transmission througli these lake waters, so 

 that it was possible to obtain resiilts at greater depths. With the present 

 galvanometer readings can be taken where the amount of solar energy is only 

 about 0.001 per cent of that delivered at the surface of the lake. The results 

 obtained at these greater depths serve to give a much better picture of the 

 light and turbidity conditions in the lower strata of some of these lakes, and 

 their relations to the photosynthesis that takes place in the deeper water. By 

 the use of color screens, also, it is now possible to determine the quality as 

 well as the quantity of light at different depths. 



Excess oxygon produced by chlorophyll-bearing organisms has been found in 

 a few of these lakes down in the region of the thermocline and the upper part 

 of the hypolimnion, and these solar-energy observations have a direct bearing 



