BIOLOGICAL SURVEY OF THE UPPER MISSISSIPPI RIVER 



139 



such a factor. To answer these questions, the following general plan of action was 

 drawn up : 



1. Collect and preserve the animals of the bottom sediments. 



2. Collect and preserve samples of surface scums, if present. 



3. Collect and preserve net plankton; enumerate after completion of the field 

 work. 



4. Collect and preserve samples of strained water, to be ccntrifuged for the 

 nannoplankton; enumerate as in 3. 



5. Make notes on submergent and littoral vegetation and on the presence of 

 coves or quiet water (source of plankton) along the shore. 



6. Seine for fish. Preserve the small ones and take notes on the larger ones. 



7. Obtain hydrometric data from the United States Geological Survey. 



8. Obtain dissolved oxygen determinations from H. R. Crohurst, who is in 

 charge of the United States Public Health Service's sanitary survey of the Upper 

 Mississippi River. 



It was decided that in order to obtain data most representative of conditions 

 in the river it would be more advisable to visit each field station two or more times 

 (until the funds were exhausted) and reduce the number of samples collected at each 

 station to a minimum than to take a large number of samples at one time and visit 

 each station once. Also, due to the limited funds, the field work was reduced to a 

 minimum. All work ordinarily performed immediately in the field, but which could 

 be postponed, was done at the University of Wisconsin. 



ACKNOWLEDGMENTS 



The writer wishes to express his gratitude to Dr. John Van Oosten, of the United 

 States Bureau of Fisheries, for making the preliminary arrangements for the survey, 

 for identifying the fishes, and for much valuable help rendered in the preparation of 

 the report; to H. R. Crohurst, of the United States Public Health Service, for 

 permission to use his data on dissolved oxygen; to Prof. Chancey Juday, of the Wis- 

 consin Geological and Natural History Survey, for the loan of a centrifuge for the 

 field work and for extending the privileges of his laboratory, where the plankton 

 and the bottom samples were studied; and to the department of zoology, Univer- 

 sity of Michigan, for the loan of the plankton pump and the plankton net. 



The writer is indebted also to Dr. Albert Mann, of the Smithsonian Institution, 

 for the identification of the diatoms in some of the samples; and to Dr. V. Sterki, 

 of New Philadelphia, Ohio, and C. F. Baker, of the Illinois Natural History Survey, 

 for the identification of the mollusks. 



The Minnesota Fish and Game Department furnished help and equipment for 

 seining; the division of sanitation of the Minnesota State Board of Health furnished 

 transportation to the station in the metropolitan area; and the biology department 

 of the University of Minnesota furnished the writer an Ekman dredge and office 

 space during the field work. The services of those responsible for these arrangements 

 are greatly appreciated. 



