466 U. S. BUREAU OF FISHERIES 



tance of some 8,280 miles. Regular fishing operations were carried 

 on from 6 Wisconsin ports, 5 Michigan ports, and 1 Illinois port. 

 The usual j^rocedure was to fish nets simultaneously out of six ports 

 and make occasional changes in the itinerary in order to cover new 

 fishing grounds. Nets with stretched meshes of the following sizes 

 were fished : 2%, 21/9, 2%, 2%, and 3 inches. Data were recorded 

 on the total bulk weights and numbers of trout and chubs taken by 

 the nets of each size mesh. Individual lengths, weights, sex, and 

 sexual maturity were recorded for all trout, and stomachs were 

 preserved from occasional samples for food studies. Chubs were 

 sorted by species, and individual biological data obtained for each 

 species to the extent that time permitted. A grand total of 1,654 

 chub nets, each 510 feet long, or, in terms of total length, 159.7 

 miles of nets, were lifted during the season. Of these nets 929 

 were fished and lifted in Wisconsin waters, 5T6 in Michigan waters, 

 and 149 in Illinois waters. 



During the 1931 season 87,018 chubs and 8,551 lake trout were 

 taken, which weighed 28,517 and 6,633 pounds, respectively. The 

 figures show that both trout and chubs are more abundant in the 

 Michigan waters than in the waters of either Wisconsin or Illinois. 

 It is possible that this difference in abundance may be attributed to 

 the larger mesh employed for chubs in the State of Michigan. 

 Throughout the season it was found necessary to fish more nets on 

 the Wisconsin shore than on the Michigan shore in order to secure 

 adequate catches for biological data. 



In addition to the fishing of experimental chub nets, certain hydro- 

 graphic data were collected whenever weather permitted. This work 

 suffered greatly during 1931 because of an unusually windy season 

 and, hence, more complete series of data could not be obtained. The 

 following data were secured in different parts of the lake : Tempera- 

 tures, plankton samples, bottom organisms, bottom soils for geologi- 

 cal analysis, and occasional transparency readings. Sixty-four soil 

 samples, 160 plankton samples, and 75 collections of bottom organ- 

 isms were secured. Temperature series in the deeper portions of the 

 lake showed many reading below 4° C, the temperature at which 

 fresh water reaches its greatest density. Bottom temperatures in 

 localities more than 150 meters deep usually showed a tendency to 

 run slightly less than 4° C. The lowest temperature obtained dur- 

 ing the season occurred in 220 meters, 32 miles W. % S. of Manistee, 

 Mich., where a reading of 3.6° C. was obtained. 



A study of the surface currents of Lake Michigan as determined 

 by drift bottles was begun on June 17 and continued until August 17. 

 Some 283 bottles were set adrift during these two months, usually in 

 transverse series across the lake. The bottles of a series were released 

 at intervals of approximately 2 miles. The southernmost series ex- 

 tended from Chicago to St. Joseph, Mich., and the northernmost 

 from Frankfort, Mich., to Kewaunee, Wis. Of the 283 bottles set 

 adrift, 180 have been recovered to date, or a percentage recovery of 

 63.6. 



The majority of the drift bottles recovered showed a tendency to 

 move northward, which was to be expected because of the prevalent 

 southwesterly winds. It is planned to continue these studies during 

 the summer of 1932. 



