NATURAL VARIATION IN SPOTTING, HYOID TEETH COUNTS, 



AND COLORATION OF YELLOWSTONE CUTTHROAT TROUT, 



SALMO CLARKI LEWISI GIRARD 



By 



Ross V. Bulkley 

 Fishery Biologist 

 Yankton, South Dakota 



ABSTRACT 



Differences in hyoid teeth and spotting counts among samples 

 from four related populations of Yellowstone cutthroat trout, Salmo 

 clarki lewisi Girard, reached species and subspecies levels as defined 

 by some workers. Body coloration varied significantly among fish in 

 six spawning runs of Yellowstone Lake, Wyo. The use of coloration, 

 spotting, and hyoid teeth counts in cutthroat trout for taxonomic purposes 

 needs reevaluation. 



Early descriptions of the cutthroat trout, 

 Salmo clarki , stressed its brilliant body colora- 

 tion and spotting, and the presence of 

 basibranchial teeth. Field collections of this 

 species are still being divided into subspecies 

 and separated from rainbow trout (Salmo 

 gairdneri ) on the basis of these characters 

 (e.g. Needham and Gard, 1959, and Quadri, 

 1959), even though wide variations in colora- 

 tion, spotting, and number of hyoid teeth can 

 be found within a single population. The present 

 study was initiated in 1959 to determine the 

 amount of variation in these characters within 

 four related populations of Yellowstone cutthroat 

 trout, Salmo clarki lewisi Girard. The results 

 illustrate the extreme plasticity of the Yellow- 

 stone cutthroat in regard to the above characters 

 and the hazards involved in separating field 

 specimens into taxonomic divisions on the basis 

 of one or two characters. 



Populations studied 



Collections of fish for meristic counts 

 were obtained in 1960 from traps at the mouths 

 of Arnica, Pelican, Grouse, and Chipmunk 

 Creeks as fish entered these streams from 



Yellowstone Lake to spawn (fig. 1) and from 

 Bear and Sedge Creeks, which are tributaries 

 of Turbid Lake, and in 1961 from the Creston 

 National Fish Hatchery at Kalispell, Mont. 

 Turbid Lake is a large thermal spring and is 

 an effective barrier to fish movement. Data 

 on coloration were obtained in 1959 at traps on 

 Arnica, Pelican, Clear, Cub, Chipmunk, and 

 Grouse Creeks as the fish ran upstream from 

 Yellowstone Lake to spawn. 



Cutthroat in Yellowstone Lake are a 

 composite group representing fish which hatch 

 out in a number of different tributaries . Adults 

 move into these tributaries to spawn and then 

 return to the lake. The young migrate down- 

 stream to the lake usually during the first 2 

 years of life. The Creston hatchery has main- 

 tained a brood stock of cutthroat from eggs 

 obtained at Yellowstone Lake in 1948. Fish of 

 age group III in 1961 represented the fourth 

 generation from wild stock . The fastest growing 

 fish of each generation were retained for brood 

 stock, but no other selection occurred and no 

 mixing with other cutthroat strains was allowed. i'^ 



Present address of author: Box 60, Nukulafa Tongatapu, Tonga, 



Friendly Islands, SOUTH PACIFIC 

 1/Personal correspondence from Blendon H. Cook, Supt., Creston NFH, Kalispell, Mont. 



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