Table 1 . --Returns of tagged fish to Lake Yellowstone streams, 



1949 - 1955. 



Number Total number returned Number to Number to 



Stream tagged in later spawning runs original stream other stream 



74 

 8 

 44 

 30 

 88 



Totals 



18,836 



244 



236 



Time of migration - -The migrational pat- 

 terns of spawners entering tributaries exhibit 

 differences from stream to stream . In some 

 years spawning in all tributaries may be a week 

 or two earlier or later than in the average 

 year, but the patterns persist. Fishery work- 

 ers at Yellowstone recognize "early" and late" 

 streams, and these temporal characteristics 

 appear in remarkable fashion through the years . 

 Their constancy is put to practical use in 

 scheduling the installation of fish traps each 

 year; it is commonly known, for instance, that 

 the trap in Cub Creek need not be installed be- 

 fore June 1, because Cub Creek is a "late" 

 stream . 



Another feature of these migrational pat- 

 terns pertains to the length of time of the run, 

 and still another to the distribution of the run in 

 relation to time. These principles are seen in 

 figure 2, showing some time -of -spawning char- 

 acteristics in five spawning streams. Each 

 curve is typical of one stream, being based on 

 five years' counts . 



The five streams show five different pat- 

 terns Pelican Creek has an early run which 

 peaks in early June, has a second peak in late 

 June, and lasts until late July. Chipmunk Creek 

 begins early (the curve suggests that a portion 

 of the run may enter the stream even before the 

 trap is installed) and extends to the end of July. 

 These runs show a very definite bimodal feature, 

 with both peaks at about the same level. Grouse 

 Creek, located close to Chipmunk Creek in the 

 South Arm, shows the bimodal quality, but with 



a definite emphasis later in the season. Grouse 

 Creek starts later than Chipmunk, ends at about 

 the same time, but has its second peak domin - 

 ating the distribution . Clear Creek, essentially 

 a late run stream, has a suggestion of a mode in 

 early June, but by far the greatest portion of the 

 migration occurs in the middle of July. Cub 

 Creek shows one great, late surge in early and 

 middle July, and rapidly diminishes in late July. 



These migration characteristics, occur- 

 ring in fairly constant patterns every year, 

 appear to be, in at least some cases, responses 

 to temperature characteristics in the streams. 

 Arnica Creek, an early run stream, ordinarily 

 has maximum daily water temperatures in early 

 June well above 50° F. Grouse Creek, a late 

 stream, averages close to 45° at this time, while 

 Chipmunk and Pelican Creeks average about 50° . 

 The notable point here is that, if times of migra- 

 tion are partly responses to temperatures, only 

 the fish related to specific streams respond and 

 enter these streams. The lake contains a mix- 

 ture of fish from several streams, many having 

 the opportunity to take part in each migration as 

 it occurs. But, each group segregates from the 

 mixture at the proper time and enters its own 

 stream . 



Sizes of fish- -The recognition of races 

 of fish is often accomplished by demonstrating 

 statistically significant differences in sizes of 

 fish. The differences are presumably due to 

 differences either in growth rate or in age com- 

 position . Such differences have been reported 

 for cutthroat trout in spawning runs and in the 



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