106 
BULLETIN OF THE BUREAU OF FISHERIES 
in question, and if our knowledge of the movements of fishes were complete it would be 
possible to answer in brief and definite terms the question of the significance of the 
dam as a barrier. That knowledge is as yet too incomplete, but, before listing and 
discussing the species of fish collected in the vicinity of Keokuk in the light of what 
we know of their movements (Coker, 1930), we may present in summary form the 
results of our inquiry as to whether or not there is evidence that any considerable 
migration of fish past Keokuk had existed and been checked by the dam and whether 
or not such interference with the movements of fish, if it exists, is of economic 
consequence. 
EVIDENCE OF MIGRATION 
On the whole, there has been discovered much less evidence of extensive migra- 
tion passing or attempting to pass Keokuk than had been expected. The degree of 
abundance of fishes at Keokuk after the completion of the dam (see p. 94) indicated 
some sort of migration of paddlefish, river herring, Ohio shad, and possibly buffalo 
fishes, and subsequent observations have tended to confirm this indication. 
Persistent watching for the gathering of fish about the dam, power house, and 
lock during 1915 and 1916, and evidence of various sorts accumulated in those 
years, made it appear that the structures also stopped some upstream movements 
of shortnose gar, carp, drum, and perhaps shovelnose sturgeon and three species of 
catfishes. Movements of the sauger may, perhaps, be checked in winter. We may 
well expect a decline in abundance of the eel above Keokuk. All of these species are 
of economic value, but the desirable characteristics of the gar are offset by other 
traits, and some reduction in its abundance will not be generally deplored. From 
what we know of the life histories of fishes it is believed that only the river herring 
and Ohio shad will have their spawning seriously interfered with, and this could be 
a matter of distinct economic importance in the case of the herring for reasons stated 
in the companion report. (Coker, 1930.) If the eel, one species of catfish, and 
possibly the paddlefish are substantially excluded from the upper river, there will 
result a loss of fishery products valued at a few thousand dollars annually. The 
checking of migratory movements by buffalo fishes and carp is not believed to be of 
economic significance, and probably the same is true in the case of the shovelnose 
sturgeon, two species of catfishes, the sauger, and the drum. 
A very simple explanation may be offered for the upstream migratory tendency 
on the part of all of the species just mentioned (except the herring and Ohio shad) 
and doubtless for many other fishes. 
It might be safely assumed that most fishes have periods of inactivity or of 
reduced activity. In aquaria it has been observed that such periods occur with 
yellow perch and black bass (Townsend, 1916); the carp hibernates (Hessel, 1878, 
p. 869), and observations elsewhere reported (Coker, 1930) indicate clearly that the 
same is true of the drum. Very probably they seek still places in which to spend 
their quiescent intervals, but nevertheless, they must be swept downward frequently, 
and even when not hibernating they must often be carried downstream. 
If fish drift down with the current at any season, they must work upward or 
against the current at another, unless the upper parts of streams are to be entirely 
depleted. From this aspect it is a matter of indifference what the cause of the 
movement may be — necessity to find breeding grounds, to secure food, to encounter 
different temperatures, or something else. In such case an obstruction midway of 
a stream, which checks downward movement as well as upward migration, has no 
