KEOKUK DAM 
107 
material effect upon the abundance of fish above and below the obstruction, although 
local and seasonal distribution of fish may be modified somewhat. Stoppage of current, 
as in a pool, must check downward drift independently of a structural barrier. 
In some cases these upward and downward movements extend for such a short 
distance that the species may exist above a dam placed close to the headwaters of a 
stream. However, we would expect to find fewer species above than below such 
a barrier, because those engaging in more extended migrations would not have a 
sufficiently extended range above. 
Hankinson (1910) made an interesting study of the fishes in a small creek near 
Charleston, 111. Seventeen species were collected, of which seven were common and 
permanent and three others were common at times. Even within the limits of this 
creek there appeared to be upward and downward movements, for during one spring 
a minnow ( Campostoma anomalum ) was abundant below but not above a temporary 
barrier until the barrier was washed out, and thereafter it was abundant farther up 
the stream. The author did not find any relation between temperature and the 
presence of fish (species not stated) ; the largest aggregation was seen on January 28, 
when, with the water a few degrees above freezing, examples of the minnow just 
mentioned were feeding. This is particularly interesting in its bearing on the 
hypothesis that has been suggested. If, as indicated by the observations of Han- 
kinson, some species are active throughout the year, it is evident that they might 
maintain themselves in the headwaters of a stream without engaging in any con- 
siderable migratory movements. Further study may show that there is some 
relation between the extent to which river fish migrate and the extent to which they 
hibernate or aestivate, and that one habit is associated with the other in the case of 
species inhabiting running water. 
Parenthetically, it should be stated that the hibernation or aestivation of fishes 
is probably less profound than that of mammals, the organs of locomotion, for instance, 
being used moderately. (Townsend, 1916.) 
The migration of our inland fishes appears, for the most part, to be of the char- 
acter that has been outlined. Obviously, movements of this sort might be checked 
at the middle of the range of a species without any result more serious than a limited 
seasonal gathering of fish below the dam and either a slight depletion of the upper 
river, by fish dropping down and being carried over the dam, or, where there is a 
lake above, the temporary accumulation of drifted fish above. If the barrier occurs 
near the limit of the range of a species that engages in this relatively slight sort of 
migration, that species might well be excluded from the upper side of the dam, and 
this probably has happened at Keokuk with the Fulton catfish. 
Fishes that engage in extensive migrations to spawning grounds above the point 
where the dam is located would be affected more seriously because reproduction would 
be diminished or altogether prevented. Examples of this class are the Ohio shad and 
probably the river herring. The catadromous eel may be excluded from the upper 
river, thus having its range diminished though its spawning is not interfered with. 
ALLEGED DIVERSION OF FISH UP THE DES MOINES RIVER 
The Des Moines River enters the Mississippi about 3 miles below the dam, and 
the suggestion has naturally occurred to some that the dam would divert fish up this 
tributary. In September, 1913, shortly after the completion of the dam, reports 
reached the author that the Des Moines River at Ottumwa was filled with fish 
alleged to have been deflected up that river by the dam at Keokuk, He proceeded at 
