RACES OF CUTTHROAT TROUT 

 IN YELLOWSTONE LAKE 



By 



Oliver B . Cope- 



1/ 



Most trout populations in the United 

 States are not well suited for studies on races 

 because of our lack of knowledge of their identi- 

 ties. Since before the turn of the century, 

 American fishery workers have energetically 

 introduced trouts into barren waters and added 

 to already existing populations. This has re- 

 sulted in hybridization between species, inter- 

 breeding of subspecies, and the mixing of races, 

 both in nature and in fish cultural establishments . 

 Records have been poorly kept or lost in many 

 instances, so the resulting trout populations 

 in most of our waters are not accurately known 

 as to origin, and studies on established races 

 would be most difficult to approach . 



In many cases where exact identities are 

 known, the trout have been introduced so re - 

 cently that there has not been sufficient time 

 for races to separate or form. In other in- 

 stances where pure stocks were recognized, 

 they have recently become extinct, as with the 

 Utah cutthroat, Salmo clarki Utah Suckley, and 

 the Lahontan cutthroat, Salmo clarki henshawi 

 Gill & Jordan (Miller, 1950) . " 



Yellowstone Lake in Wyoming supports a 

 stock of the Yellowstone cutthroat, Salmo 

 clarki lewisi (Girard), that has remained free 

 of the influences of any trout from outside the 

 drainage . No other species of trout have been 

 introduced, and no cutthroat from other waters 

 have entered the lake or its tributaries, save 

 perhaps a small number of Snake River cut- 

 throat that may have wandered in through the 

 original avenue of natural stocking. 



The cutthroat in Yellowstone Lake, then, 

 is admirably fitted for studies on its races. 



1/ Chief, Rocky Mountain Fishery Investigations, 

 U. S.Fish and Wildlife Service, 

 Forestry Building Utah State University 

 Logan, Utah 



The stock has been virtually pure for a long 

 time, the geography is well adapted for such 

 studies, and enough biological investigation has 

 been carried on to provide a moderate accumula- 

 tion of facts on which to base an inquiry into the 

 formation and existence of races. 



TERMINOLOGY 



Many terms have been used to designate 

 taxonomic groups of animals below the species 

 level. The subspecies is the most widely used 

 such designation in zoology, and is defined by 

 Mayr, Linsley, and Usinger (1953) as "geo- 

 graphically isolated aggregates of local popula- 

 tions which differ taxonomically from other such 

 subdivisions of a species." Other names are 

 sometimes used synonymously with the term 

 "subspecies", the term "race" being in use by 

 many groups of zoologists. Fish terminology 

 often utilizes the "race" in designating popula- 

 tions within the subspecies, and it is in this 

 sense that the name "race , or "local race" is 

 used here. Other names, such as "sub-popula- 

 tion, might be used, but not the term "subspecies", 

 since it is obvious that we are dealing with 

 separate populations within a group considered 

 by ichthyologists to be a valid subspecies . 



Races have been described in several 

 ways. The "geographical race" is localized geo- 

 graphically, and the "ecological race" is localized 

 ecologically. However, since no two localities 

 are alike ecologically (Mayr, et al, 1953), the 

 two are alike. "Physiological races" are those 

 which differ from related populations in some 

 physiological way, as with "temperature races" 

 Temperature races are those having particular 

 temperature preferences or tolerances, and are 

 common in fish, whose dependence upon the 

 temperature of the environment is greater than 

 that of warm-blooded animals . Other physio- 

 logical races differ from their close relatives 



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