724 BULLETIN OF THE BUREAU OF FISHERIES. 



RESCUE OF FISHES FROM OVERFLOWED LANDS. 



In the upper Mississippi and Illinois rivers there is an annual spring flood 

 period caused by the melting of the snow in the northern forests and freshets 

 in the local tributaries after heavy rains. The period begins with the approach 

 of warm weather, usually about March 15, and continues until about June i, 

 when the crest of the high water has been reached. Soon after this date the 

 water begins slowly to recede, and usually by July 15 the river has reached its 

 normal stage. 



Between the extreme low and high water marks there is a variation of 12 

 or 15 feet. There is, of course, a variation in the extremes of the water level in 

 different seasons, but seldom, if ever, does the water fail to rise high enough to 

 flood the lowlands. The adult fishes are thus permitted to enter the overflow 

 basins and bayous, and invariably do so during the spawning season. After 

 spawning most of the adult fish escape to the river before the water has receded 

 sufficiently to cause them to be hemmed in, but immense numbers of their 

 progeny are left in the lakes and bayous where they were hatched. These waters 

 gradually dry up, become choked with vegetation, or overheated and unfit for 

 fish life; some of the larger and deeper lakes and bayous, although cut off from 

 the main river, may contain water the year around, but on account of the 

 seepage and evaporation during the summer the depth of water in them de- 

 creases to such an extent that they freeze solid during the winter months. 

 Sometimes the lakes from which fishes are rescued are in the hollows on farm 

 lands, where in dry seasons crops are cultivated. Thus it will be seen that the 

 fish imprisoned in overflow waters are doomed to destruction in one way or 

 another. 



One branch of the Bureau's operations is annually to rescue large numbers of 

 these fishes. At present the work is confined to waters convenient of access — 

 namely, the overflow lakes and bayous on the low islands in the rivers and on 

 the adjacent mainland. Many of the fishes are returned to the rivers. Another 

 portion of the more desirable species is distributed in various other waters, 

 often far from the source of supply. 



It has been found, however, that the fishes rescued from these warm waters 

 do not bear transportation long distances without heavy losses if immediately 

 started upon their journey. Therefore a hardening process is resorted to, which 

 consists in holding the fish in large tanks flowing through which are streams of 

 clear cool water. To facilitate the work the Bureau has a number of field 

 stations — one on the Illinois River and three on the Mississippi — convenient of 

 access to the railroad, and each equipped for holding one or more carloads of 

 fishes for several days, or until they have become sufficiently hardened to bear 

 transportation by cars. Adjunct to these stations are vessels, launches, and 

 boats of various types suited to the work. 



