in factors of sex and reproduction, and are 

 known as "sex races' . Ecological races of 

 other kinds have been described as "seasonal 

 races" which cannot mate with other races be- 

 cause the times of reproduction do not coincide, 

 and "altitudinal races", which are races sep- 

 arated altitudinally from others . 



Salmo clarki lewisi in Yellowstone Laice 

 probably is divided into races of several of the 

 kinds noted above. It may be that races should 

 not be differentiated so delicately, since many 

 are considered to be synonymous. The fact re- 

 mains, however, that factors of time, space, 

 and ecology are involved here, and must be 

 used in the analysis to elaborate on the existence 

 of local races . 



YELLOWSTONE LAKE 



Yellowstone River originates atop the 

 Continental Divide, draining to the north from 

 Atlantic Creek and Two-ocean Pass. After flow- 

 ing about 30 miles northward, the river enters 

 Yellowstone LaKe (fig. 1). The Yellowstone 

 River drains from the north end of the lake and 

 flows approximately 15 miles before reaching 

 the Upper Falls of the Yellowstone, an impass- 

 able barrier 109 feet in height. Two -ocean 

 Pass is also the origin of a branch of the Snake 

 River, flowing to the west from Pacific Creek . 



Yellowstone Laice lies at an altitude of 

 7,750 feet above sea level, and is 139 square 

 miles in area. The lake is divided into several 

 large arms and bays, and its irregular shore- 

 line measures over 100 miles. Approximately 

 35 tributary streams enter the lake, and most 

 of them support the spawning of cutthroat trout. 

 The Yellowstone River below the lake is also 

 used by trout for spawning. 



The streams tributary to Yellowstone Lake 

 are diverse in size, in temperature patterns, in 

 flow, and in their chemistry. Many of them re- 

 ceive discharges from hot mineral springs, and 

 high temperatures and pollution intolerable to 

 cutthroat are present at some times in many 

 streams. This diversity in the environment of 

 the trout appears to have had some bearing on 

 the formation of races within the lake and stream 

 system . Variations in physical and chemical 

 conditions also exist from place to place in the 



lake, and the distribution of groups of fish in the 

 arms of the lake may be related to such environ- 

 mental differences. 



The Yellowstone cutthroat apparently 

 came to Yellowstone Lake from the west, despite 

 the fact that the lake lies east of the Continental 

 Divide and drains into the Gulf of Mexico via the 

 Yellowstone, Missouri, and Mississippi Rivers . 

 Two -ocean Pass, mentioned above, lies astride 

 the Continental Divide just south of Yellowstone 

 Park . At times waters from the area flow into 

 the Yellowstone and Snake drainages, and a continu- 

 ous waterway is formed. Evermann (1893), after 



visiting the area, said, " and there is 



no doubt whatever that trout can and do pass over 

 this divide at will.' He further stated, "Evidently 

 Yellowstone Lake and the Upper Yellowstone 

 River were stocked from the west, and almost 

 certainly via Two-ocean Pass. The probability 

 that the outlet of Yellowstone Lake at one time 

 was toward the Pacific, as claimed by geologists, 

 only strengthens this solution of the problem . 

 But if this explains the origin of the trout of Yel- 

 lowstone Lake, it leaves another equally interest- 

 ing problem without any explanation, viz . , the 

 presence of the blob ( Cottus bairdi punctulatus ) 

 in Pacific Creek and its absence from Atlantic 

 Creek and the entire basin of Yellowstone Lake." 

 Other theories have been advanced to explain 

 the introduction of trout into this drainage, but, 

 whatever route was used, the fish apparently 

 have been established for a long time. Observers 

 claim that trout today can pass over Two-ocean 

 Pass, but no one holds that there is any consider- 

 able traffic across the top. The trout above the 

 falls in the Yellowstone are, therefore, almost 

 isolated in this drainage and represent the taxo- 

 nomic entity Salmo clarki lewisi in its native 

 waters . 



LIFE HISTORY 



The Yellowstone cutthroat in Yellowstone 

 Lake is an adfluvial fish with a life history similar 

 to those of several other inland cutthroats. Eggs 

 are deposited in shallow redds in the gravels of 

 streams tributary to the lake. Upon hatching, 

 the fry may either move immediately downstream 

 to the lake, may linger in the stream for a few 

 months before descending to the lake, may spend 

 the first winter in the stream, or may spend 

 two or more winters in the stream . Most of 



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