PROGRESS IN BIOLOGICAL INQUIRIES, 19 30 623 



Concerning the removal of silt it was found that such silt as is 

 taken out of the water by the fresh-water mussels is returned to 

 the stream in the form of small globular masses in which the slit is 

 bound together with nuicus secreted by the mussel, and that these 

 masses sul)sequently disintegrate so that the silt has been removed 

 only temporarily from the stream. 



The bacterialstudies carried along with these activity experiments 

 have shown that in material taken into the alimentary canal of 

 the mussels the bacteria may pass through the mussel unaffected, 

 to be returned to river water in less than five hours, so that the reduc- 

 tion of bacteria in river water by mussels not only does not take place 

 but in many experiments it was found that the number of bacteria 

 in the water actually increased after the mussel was placed in the 

 water. 



SURVEY OF UPPER MISSISSIPPI RIVER 



From June 29 to September 6, inclusive, the personnel of the Colum- 

 bia unit was engaged in a survey of the Mississippi River from 

 Quincy, 111., to Point au Sable, Minn., in Lake Pepin, conducted 

 jointly by the Corps of Engineers, U. S. Army, and the U. S. Bu- 

 reau of Fisheries to consider the probable effects of the changes in 

 the Mississippi River incident to construction of the proposed 9-foot 

 channel. This surve}^ gave particular attention to the changes Avhich 

 have been produced in the Mississippi River and its fauna and flora 

 by the Keokuk Dam and by the various wing dams which have been 

 constructed as aids to navigation. 



U. S. Engineer quarterboat No. 34S (Fig. 9) was placed at the 

 disposal of the U. S. Bureau of Fisheries, and was used throughout 

 the summer as a floating laboratory. Ample equipment was taken 

 aboard to provide for tlie chemical, physical, bacteriological, and 

 biological work in the field, and the preserved material was for- 

 warded to the Columbia laboratory for final study. 



Fresh-water mussels, fish, and fish food were collected and studied, 

 and detailed chemical and physiological analyses of both the water 

 and the river bottom were made throughout the summer. Individual 

 observations on over G,500 fresh-water mussels above were made dur- 

 ing the course of this work and large quantities of other material 

 taken. 



In the main the results of this work may be summarized as 

 follows : 



There are three major factors at work at present changing the 

 fisheries situation in the Mississippi and each of these combines with 

 the other two in accelerating the change now going forward. 



(a) Construction and reclamation of flooded land by dikes and 

 pumping stations have reduced the lateral shore zones of shallow 

 water in many places along the Mississippi to such an extent that 

 suitable spawning grounds and shallow waters in which young fish 

 may thrive are practically wanting. With the loss of these lateral 

 zones of shallow water the production of plankton, the basic fish 

 food, has been greatly reduced in certain parts of the river. 



(&) Municipal and industrial wastes, sewage and factory run-offs 

 in particular, have so polluted many sections of the river that only 

 those animals capable of existing under very adverse conditions are 

 able to maintain themselves. This problem is acute in many places 



