FISHES OF COLORADO 1 27 



level makes possible a broad zone of aquatic shore vegetation (Fig. 

 56), and the absence of a current allows the deposition of silt and 

 water-logged material. Into these lakes various species of eastern 

 Centrarchidae and Percidae have been introduced with success. Other 

 lakes have been stocked with catfish. 



Changes in the Fish Fauna of Colorado 



From geological data it is known that portions of Colorado have 

 been covered with salt water at times. Traces of the marine faunas 

 occurring during these inundations are now found in fossil oysters, 

 fishes and other animals taken from the rocks. The earher of these 

 deposits contain remains of sharks and chimeras. From more recent 

 deposits in a fresh-water lake, existing at one time near Florissant, 

 remains of several species of suckers and of two species of bowfins 

 have been collected. These fossils show that there have been changes 

 in even the fresh-water fish fauna of Colorado." 



Observations on the changes in the fish fauna of the western part 

 of the United States since the advent of man are very few and the data 

 existing have no large value in relation to the evolutionary changes, 

 since they have been collected in rather recent times only. Chief 

 among the disturbing factors in recent years has been civilization. 

 In Colorado, man has changed the fish fauna in at least the following 

 ways : (a) by removing large nimibers of native fishes for food without 

 properly restocking the streams; {h) by deflecting water for irrigation, 

 leaving the streams low or even dry in some seasons; (c) by allowing 

 the fishes to run into unscreened ditches only to become stranded and 

 die in the fields; {d) by the introduction of mine and mill waste, the 

 poisons from which often kill large numbers of fishes in a single day; 

 {e) by the introduction of other fishes which become competitors of 

 the native species. 



The first item, overfishing, afifects the trout more than the other 

 species, and need be discussed but briefly. It is a matter of general 

 knowledge that trout were once abundant in many streams where 



■ For a list of the fossil fishes of the Rocky Mountain region see Cockerell, Univ. Colo. Studies, Vol. V, 

 pp. 161 f., igoS. 



