1160 U. S. BUREAU OF FISHERIES 



UPPEU MISSISSII'PI WILD LIFE AND FISH REFUGE 



The following report is submitted covering the biological investi- 

 gations in the Upper Mississippi Wild Life and Fish Refuge : 



Detailed quantitative biological studies of five slouglis in tlie vicinity of 

 Trempealeau (Wis.) and Winona (Minn.) were made at 2-\veek intervals 

 throughout the year, summer and winter. Studies were made of bottom and 

 weed fauna populations, plankton, and chemical conditions. These observa- 

 tions in a general way revealed that these sloughs differ widely in production 

 of natural food, that the bottom and weed fauna populations are apparently 

 composed of few species, but large numl)ers of individuals, and that the cliar- 

 acter of the bottom of a slough can be used in predicting the quantity and 

 diversity of food it contains. Oxygen samples, taken in winter beneath the 

 ice, showed that the oxygen supplies of the sloughs investigated were exhausted 

 by the end of January. This condition would not permit the holding of fish 

 in them through the winter, though river stages would usually permit it. Since 

 all fish landlocked in sloughs are likely to die before the end of January, and 

 since it appears to be impossible to rescue all large fish in them, it would 

 seem advisable to permit early winter fishing in them, provided such fishing 

 would not result in illegal fishing in waters o))en to the river. Complete 

 analy.sis of the data collected in these studies will not be possible for several: 

 months. 



Fish population records of all sloughs seined thus far in our operations sluiw 

 that the pickerel is the most important fish enemy of game fish in the sloughs. 

 Legislation permitting the taking of pickerel 20 inches or more in length by 

 commercial fishermen within the refuge limits would probably result in an 

 increase in the numbers of other species of more desirable game fish. 



In fish-cultural practice in the sloughs, screens should be put in and the 

 pickerel removed as soon as the ice goes out in the spring and a favorable river 

 stage permits. Although this was done in the spring (if 1980, it probably will 

 not be possii)le to remove the adult iiickerel before they have spawned. In 

 the latter case the seining of the sloughs, wh'cli are to he used as rearing i)onds 

 for bass, would have to be postponed until just l)efore the bass fry are planted 

 in them. 



^Examination of river-stage records for this locality shows that the Missis- 

 sipiii Kiver in recent years stldom exceeds the 6-foot stage during the last week 

 in May and throughout June. This will make possible beyond doubt the 

 production of Hngerling bass running into the hundreds of thousands in sloughs 

 in this locality, though some years are going to be comparative failures. Dur- 

 ing the current year 1.35,000 bass fry were transferred to sloughs prior to 

 June 30. The exprimental results from these plantings will be affected tO' 

 an uncertain extent, however, by two rises exceeding the 7-foot stage at 

 Trempealeau during the critical peridd. 



Experience during the current year has shown that bass fry less than 

 five-eighths of an inch long apparently exhibit strong negative rheotropisni. 

 Losses of fry from our large brood pond were experienced when fry passed 

 through the meshes of the screens (7 meshes to the inch) used to shut 

 the pond off from a slough below connecting it eventually with the river. 

 These losses occurred when the river was dnipping rapidly or a current 

 was passing through the pond during high-water periods. Precautions will 

 be taken during another season to place our brood stock in sloughs from which 

 there is no outflow or appreciable passing through. 



Experiments in the control of vegetation with sodium arsenite solution were 

 made during the summer of 1920. It was found that amounts of the chemical 

 up to about 1.7 parts per million arsenious oxide could be used with good results 

 w thout exterminating microscopic or macroscopic lish food organisms. The 

 chemical was applied to the sloughs believed to need treatment early in spring, 

 during a low-water period, before rapid development of vegetation had gotten 

 under way. 



In further connection with the bureau's operations a Si/o-acre tract 

 in the refuge adjoining the La Crosse hatchery was cleared for the 

 purpose of constructing a bass pond to be supplied with artesian 

 water. A number of inspections were made throughout the refuge 

 for the purpose of locating sites suitable for bass culture, but it was 



