COMMON PISHES OP MISSISSIPPI RIVER 
199 
The cause of this remarkable aggregation of fish was fairly obvious. On July 13 
and 14 there had occurred a great emergence of May flies, Hexagenia bilineata , 23 
and millions were floating dead on the surface of the lake. On the 15th the prevailing 
wind, as shown by records of the local office of the Weather Bureau, was from the 
southeast, but on the 16th it came from the north and on the 17th from the northeast, 
driving the surface drift toward the lock and the chute, below which the carp were 
seen. At the time of the observation (May 17) an enormous and noisome mass of 
bodies of May flies, mingled with casts and with duckweed, had accumulated near 
the lock, and a steady stream of this matter was flowing through the chute. The 
carp were evidently snapping at the generous food supply. Nine carp were dipped up 
for examination, and although two had empty stomachs the remaining seven were 
found to contain duckweed and remains of adult May flies, chiefly the latter. Early 
the next morning, after the accumulated mass of May flies and weed had been forced 
out through the chute by the lockmen, both May flies and fish had disappeared. 
Observations could not be continued by Stringham, but the following notes made by 
Mr. Raber, lockman on duty from midnight to 8 a. nr., are significant: 
July 19. Wind southwest. Not more than a dozen fish visible at one time. 
July 20. Wind north. Several hundred fish, mostly by spillway (chute). 
July 21. Wind north. Couple of dozen fish visible at a time when there was food. 
Mr. Raber’s notes were found, upon inquiry from others, to be representative of 
the conditions throughout the period. During the remainder of the month a few 
carp were occasionally seen below the chute. 
These observations, we think, are of real importance, because it is so generally 
assumed, when fish are congregated below falls or dams, that they are necessarily 
endeavoring to pass upstream, whereas there may be various conditions at the bases 
of falls to attract fish that have no decided migratory urge. Of such conditions are 
the exceptional degree of oxygenation of water below falls and, as in this case, the 
presence of food in unusual quantity. 
The nomadic tendencies of carp have been commented upon by Cole (1905, 
p. 556-561). Another series of observations is pertinent. In 1916 carp were taken 
on the lock gate principally in August. The height of the movement was between 
August 6 and 12, but during each week of the month there were taken from three to 
ten times as many carp as were taken during any other week of the year. Stringham 
saw 300 carp shoveled from the gate on August 26. The spawning season was cer- 
tainly closed before August. It should be noted that the abundance in the lock was 
very local, not being reflected in the catches brought to near-by markets; even the 
inclosure of the power house had, as already said, fewer fish in evidence during 
August. 
From information obtained personally in 1926 it appeared that the reduced 
abundance of carp in Lake Keokuk, indicated by the statistical survey of 1922, still 
prevailed. There was general complaint along the shores of the lake of the relative 
scarcity of small carp. Most of the carp taken were very large. The carp of the lake, 
like the buffalo fishes, brought relatively high prices in the New York market. Ac- 
cording to a reliable informant, when carp taken below the dam must be sold at 5 
cents a pound those from the lake might bring 22 cents. The relative scarcity of 
small carp, as reported, and the fine condition of those taken in the lake bear out 
the supposition that the reduction in abundance of carp in the lake is attributable 
23 For details see Needham, 1920, p. 272, quoting observations of Stringham. 
