248 " Roosevelt Wild Life BuUcdn 



GENERAL PRINCIPLES OF STOCKING INLAND WATERS 



As pertains to stocking or restocking of waters, there are a 

 number of essential ecological conditions that require attention. It is 

 desirable to know not only to what kinds of fish a body of water 

 is suited but also how many of each kind it can sustain, maintain and 

 retain. Its sustaining power in a measure depends upon the quantit}- 

 and quality of the food supply; that of maintenance depends upon 

 the perpetuit}' of its food supply and upon adequate breeding places, 

 or annual plants of fish ; the number that can be retained depends 

 upon the habits of the fish, intercommunications of waters and the 

 control of the fishery. One of the essential conditions to consider, 

 then, is biological capacity. 



Food Producing Capacity o£ Fresh Waters. It has been long 

 known that the try of a great number of fishes feed upon minute 

 Crustacea and small insect lar\^ae which live in the water. Because 

 of this relation, for many years it seemed that the solution of fish 

 culture depended to quite a degree upon our knowledge of these 

 small organisms, both plant and animal, which floated about in the 

 water, the plankton. This stimulated many quantitative studies of 

 the plankton in the Great Lakes and other smaller ones by Reighard. 

 Ward, Birge, Marsh, Tuday, and others, particularly in the lakes 

 of Michigan and Wisconsin. Kofoid made an extensive study of 

 the plankton of the Illinois River ('03, '08) and his investigations, 

 among other conclusions, led him to believe that the submerged 

 aquatic plants were a vital factor in the production of plankton ; the 

 more abundant this vegetation, the less abundant the plankton. 

 Pond ('05) later modified this conclusion and showed that the 

 amount of plankton, other things being equal, is in an inverse ratio 

 to the amount of its gross non-rooted vegetation, and in a direct 

 ratio proportional to the amount of its gross rooted vegetation 

 ^figures 24. 25). He concludes as follows (p. 525): "If we 

 accept the conclusions reached in this paper that gross rooted vegeta- 

 tion is favorable to plankton production, and if we further accept 

 the current argument that fish production is dependent on plankton 

 production, the practical applications of the results of this investiga- 

 tion are simple. In the stocking of ponds for fish culture care 

 should be taken to have a good soil for the bottom ; not a stiff clay 

 nor sand, but a ^ood loamy soil, such as is favorable for land 

 plants. The species allowed to grow should be those which are 

 known to possess roots and to be ver}' dependent upon the soil, 

 such as Vallistieria spiralis, the so-called eelgrass, and Potamogeton, 

 or pond weeds ; not forms without roots, such as CeratophyUum. or 

 those less dependent upon the soil. In natural lakes choked with a 

 growth of Ceratophylhim, the removal of this form and the sub- 

 stitution for it of rooted plants offer possible means of increasing 

 the supply of edible fish. 



" The povertv of the Great Lakes in plankton may Ije attributed 

 to several causes. One of these is. doubtless, the relatively small 

 shore area in these waters occupied by rooted aquatics. The com- 



