The Migration of Illinois Fishes 
by 
David H. Thompson 
About 7,000 Illinois fishes of the larger and more important 
kinds have been marked with serially numbered tags and released in 
the principal streams and lakes of the state. At present we have 
sufficiently detailed information on the time and place of recapture 
of more than 120 of these tagged fishes to warrant a preliminary re- 
port. Beginning in 1929, Illinois has suffered four years of extreme 
drouth., During these years unusually low stages of water have pre- 
vailed in all of our streams. Since most of these fishes bore tags 
during this period, the results which we have obtained may reflect 
in some degree the effects of drouth on fish movements. 
It has been found that the movements of fishes as deter- 
mined by tagging are random in nature, at least in their general 
aspects and over considerable periods of time, This randomness of 
their movements is shown by the fact that they are retaken at dis- 
tances from the starting point proportional to the square root of the 
time. This relationship of time and distance may be utilized to 
estimate average distances from the starting point. These calculated 
average distances are shown in Table I, p. 2 for periods of one day, 
one week, one month, one year, and five years. This table shows 
rather accurately the rate at which waters depleted of their fishes, 
but connected with waters containing desirable kinds, may be restocked 
by the natural movements of the fishes themselves. It also indicates 
to what degree we may expect fishes to utilize uniformly the food 
resources in the different portions of a stream or lake. 
These returns from tagged fishes have given information on 
other questions. Crapries, sunfishes, and basses move upstream 
strikingly faster than downstream, while, on the other hand, the carp 
moves downstream rather than upstream, The black bullhead makes 
rapid upstream migrations in spring and tends to mn in schools, 
since on one occasion an angler caught in one day three tagged bull- 
heads, which had been tagged 15 miles downstream 18 days earlier. A 
number of instances have given measurements of growth in length and 
weight over considerable periods of time and enables a check on the 
rates of growth obtained by counting the annual rings in scales. 
Striking differences in the capacitics of different fishes to carry 
tags have apreared, certain kinds not carrying tags more than a few 
days or weeks, while others seemingly carry tags indefinitely. 
