148 



BULLETIN OF THE BUREAU OF FISHERIES 



Four bottom samples were taken at places other than those designated as stations 

 1 to 14. One of these samples was taken immediately below the Washington Avenue 

 bridge, directly opposite the university campus. The sample contained no life of 

 any sort; it had a tarry odor and contained tar. The tar was introduced into the 

 river by a gas plant situated a short distance above the Washington Avenue bridge. 

 The waste from this plant undoubtedly explains the absence of all bottom dwelling 

 animals. The heavy tar settles to the bottom and the lighter tar and other oily 

 substances form a film on the surface. This surface film was quite pronounced on 

 some days, both as to extent and thickness. Shelford (1917) has demonstrated the 

 detrimental effect of gas-plant waste on fish. He says, in part: "Illuminating gas, 

 gas liquor, and 31 out of 34 representatives of the chief group of compounds found 

 in gas and gas liquor are very toxic to fishes." In England it has been demonstrated 

 that washings from tarred roads are killing fish in some streams. (Committee on 

 pollution, 1924-25.) 



Another sample was taken near shore behind the animal biology building at 

 the University of Minnesota. Two dredge hauls here yielded a sample of 4 liters; 

 75 cubic centimeters of this sample yielded 385 tubificid worms. This gives the 

 enormous number of 364,000 Tubificidae per square yard. The sample contained a 

 great deal of fine mud and a considerable amount of coarse organic debris. 



A third sample 1 was taken at the Lake Street bridge, about 1 mile below the 

 spot where the last-mentioned sample was taken. The sample was taken in mid- 

 stream and consisted largely of dead aquatic plants. It is the writer's opinion 

 that the dredge did not penetrate into the real sludge on account of these weeds. 

 From this sample 3,300 worms were removed. This gives a tubificid population 

 of 118,000 individuals per square yard. The data also showed that each square yard 

 contained 500 Musculium near truncatum, 72 Musculium (species unknown), and 

 72 leeches. 2 The bivalves taken were gravid. Musculium truncatum is classified as 

 unusually tolerant by Richardson (1925). 



At station No. 3, one sample was taken just above the Ford Dam, where the 

 water is taken into the power station. There is considerable current in this part of 

 the river and, therefore, the bottom is kept fairly clean. (Behind the dam proper 

 conditions are entirely different (p. 141), but no samples were obtained there.) The 

 5 dredge hauls made along shore here yielded a 200-cubic centimeter sample, which, 

 after straining, left a residue of 60 cubic centimeters. Besides the fauna, the residue 

 was composed of sand plus a small amount of organic debris. Each square yard of 

 bottom here contained 632 tubificids, 36 midge larvae, and 14 leeches. Mud scraped 

 from stones at station No. 3 contained 6,159 Tubificidse per liter. 



A third sample at station No. 3 was taken a short distance above the Ford Dam. 

 The water here is about 35 feet deep in mid-channel, and the current is very slack 

 when the water is not going through the wheels or over the dam. One haul here 

 yielded a 400-cubic centimeter sample. The entire sample was strained, leaving a 

 residue of 300 cubic centimeters. In addition to the fauna, the residue consisted of 

 coarse organic debris suggestive of garbage, cinders, and many chips of wood. The 



i The last three samples were taken between stations 2 and 3. 



1 The vast majority of the leeches were Helobdella stagnalis Blanchard. In this connection, the author wishes to acknowledge 

 the services of Dr. J. Percy Moore, whose report on leeches was of great help in identifying the species found. 



