90 
BULLETIN OF THE BUREAU OF FISHERIES 
become necessary substantially to revise them in the light of data made available in 
1922 and 1927 from the statistical canvass for those years. “Time will tell” — par- 
ticularly in the case of a substantial alteration of conditions in a natural watercourse. 
The conclusions we have reached regarding the effect of the dam at Keokuk 
upon fish life in the Mississippi must not be held to be applicable to any other darn 
except as the conditions may be strictly comparable. It is our hope, however, that 
the observations we have made and the data we have brought together throw some 
light upon the general question of dams in relation to strictly fresh-water fishes and 
also contribute something to our knowledge of the habits of fishes of the upper 
Mississippi River. 
We are well aware that there have been other significant changes in the river in 
recent years besides those associated with the dam. Notable among these are the 
changes arising from works in aid of navigation, from the development of drainage 
districts, and from increase in the amounts of sewage and industrial wastes dis- 
charged into the stream. It will be seen in our discussion of the changing condi- 
tions of the fisheries that we have not lost sight of such factors, and we believe that our 
data are so presented that it can fairly be judged whether or not our conclusions 
with regard to results following from the dam are justified. 
The report is based upon observations and other data gathered in the manner 
indicated in the following paragraphs: 
While the investigation was under the continuous direction of the author from 
its beginning in 1913, his personal visits to Keokuk and to other points on the river 
above and below Fairport, Iowa, were made only at intervals, and most frequently 
during the first two years of the investigation, when he was stationed at Fairport on 
the banks of the Mississippi. Emerson Stringham, scientific assistant, who entered 
the investigation in the second year, made occasional visits to Keokuk and other 
points during the winters of 1914-15 and 1915-16 and the summer of 1917 and 
remained on the ground at Keokuk for continuous observation during such portions 
of the years 1915 and 1916 as the river was not frozen over. Direct observations at 
Keokuk were discontinued in 1917, when a preliminary report was prepared. 3 An 
interval of years was then allowed to elapse, during which the reality of seeming 
trends might be tested by the results of later statistical studies. The last personal 
observations by the author were made in 1926, when he visited a number of points 
on the river between Lake City, Minn., and Canton, Mo. The chief object of this 
last trip was to check, by personal interviews with fishermen, the impressions derived 
from the study of statistical reports. 
Free use has been made of all available published data regarding the distribution 
and natural history of the fishes considered in this study. The records of collections 
and observations of fishes made by the various members of the staff of the Fisheries 
Biological Station at Fairport, Iowa, and its field party on Lake Pepin (Minnesota- 
Wisconsin), though not brought into this report in detail, have been invaluable. 
3 Soon after the preparation of this report Mr. Stringham left the bureau, and since that time the report has been extended 
greatly and otherwise modified in the light of new information. The senior investigator proposed to adhere to the original arrange- 
ment for joint authorship, but when the completed report was submitted to Mr. Stringham he replied that it would not be right 
to have his name upon it as joint author. The present author takes this opportunity to say that Mr. Stringham’s contributions 
to the report were very valuable, consisting in observations made on the river (especially at Keokuk), in the discriminating judg- 
ment applied to the observations, and in the assembling of literature. In regard to the literature, the present writer has personally 
examined nearly all of the publications for which references were obtained by Mr. Stringham and has been able to add a good many 
more. He assumes full responsibility for the conclusions drawn from the study, but it is not out of place to say that the final con- 
clusions .differ from^tliose that were formed jointly in 1917 in only a few important particulars, as to which revision of judgment was 
made inevitable by .the accumulation of new data. 
