222 Roosevelt Wild Life Bulletin 



ment are essential, which only desirable, which negative, and which 

 detrimental to the best life and growth of the fish. . . . This of 

 course means careful observation and study of all the physical, 

 chemical and biological features of each stream, for these are the 

 conditions, forces or elements which together constitute the fish en- 

 vironment, and which determine the presence, abundance, distribu- 

 tion, and condition of the various kinds of fishes found in each 

 particular stream or lake." 



Dr. Evermann further pointed out that the temperature and 

 chemical character of the water, the volume or size of the stream or 

 lake, the character of the shores and bottom, and the surrounding 

 country, all must be ascertained. Not only these facts, but also 

 the life histories of the fishes themselves, what other species of fish 

 and what other animals and plants are found with them, and their 

 abundance and habits, should be learned. Then after the determina- 

 tion of these facts of the fishes' environment, a second and vastly 

 more difficult series of investigation must be taken up, namely the 

 bearing of these facts upon the life of the fish. " The whole subject 

 of the relation of the various animal and plant forms found in our 

 waters, their action and reaction upon each other, and their relation 

 to the physical as distinguished from their biological environment is 

 the subject which is demanding investigation and upon which in- 

 vestigation must depend all important advances in fish culture and 

 fishery legislation." 



All this means that in undisturbed nature, there is an approximate 

 balance or counterpoise of interrelations of the organisms compos- 

 ing the animal and plant life of every body of water, subject to 

 automatic regulations. Where there is an interference, the balance 

 is tilted one way or the other in direct proportion to the amount of 

 interference. Every body of water, large or small, has a limit to 

 the amount of life it can support, and any interference that pro- 

 duces an excess of that amount, or any part of it, proportionately 

 deranges the balance. An undue reduction of any part of that life 

 may result in an over-increase of some other parts, with a final 

 result that these, or still other parts may be reduced. In other 

 words, the organisms are not only interrelated but are more or less 

 interdependent, and it cannot be foretold how far-reaching and dis- 

 astrous the effects of the destruction of any one of them might be. 



While natural phenomena may afifect the balance, the principal 

 factor of interference is man. Apparently nature did not take man 

 into consideration when she adjusted the balance, and for the reason 

 that his influence has been mainly destructive, in many instances the . 

 conditions have been so upset that he has felt called upon to efifect 

 a readjustment, which he has endeavored to accomplish by means of 

 fish culture. In his efforts in this direction he has not always been 

 guided by sound judgment, as has been shown, and too often the 

 consequences have been that sooner or later the conditions have be- 

 come worse than they were before. 



For example, there have been waters in which pike and other 

 fishes have lived in reciprocal counterpoise from time immemorial, 



