S [ree 2a. 
The Migration of Illinois Fishes 
by 
Lavid li. 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 report. Beginning in 1929, Illinois has 
suffered four years of extreme drouth. During these years un- 
usually low stages of water have prevailed in all of our streams. 
Since most of these fishes bore tags during this period, the re- 
sults 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 
determined by tagging are random in nature, at least in their 
general aspects and over considerable periods of time. This ran- 
domness of their movements is shown by the fact that they are 
retaken at distances 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, 
Pa & 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 con- 
taining 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. Crappies, 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 run in 
schools, since on one occasion an angler caught in one day three 
tagged bullheads, which had been tagged 15 milcs downstream 18 
days earlier. A number of instances have given measurements of 
growth in length and weight over considerable pcricds of time 
and cnables a check on the rates of growth obtained by counting 
the annual rings in scales. Striking differences in the capaci- 
ties of different fishes to carry tags have appeared, certain 
kinds not carrying tags more than a few days or weeks, while 
others scemingly carry tags indefinitely. 
SF Sys ee 
PU) £35 4¢ 4b 
