meters (l5.2 inches). Table 3 shows that these increases were statis- 

 tically significant. Grouse Creek j which, like Chipmunk Creek^ is tribu= 

 tary to the South Ann, also featured an increase in mean total length of 

 its spawnerso Mean total length in I9U6 was 365ol millimeters (lU=U inches), 

 in 19^1 it was 378.9 millimeters (lIio9 inches) ^ and in 19^2 it was 37U.7 

 millimeters (lit. 8 inches) , The increases from I9I46 to 19^1 and from I9U6 

 to 1952 were significant^ and the decrease from 195l to 1952 was also 

 signifi canto 



This situation, involving decreases in fish length in northern streams 

 and increases and decreases in fish length in southern streams ^ requires 

 explanation. The most obvious difference between the lake environments of 

 the two groups is in exposure to fishing pressure. Fishing pressure along 

 the northern shore of Yellowstone Lake is several times as intense as that 

 occurring in the south arm. Even though tagging results show that Chipmunk 

 and Grouse Creek fish frequent West Thumb at times, and that Pelican Creek 

 fish often inhabit areas south of the mouth of Pelican Creek j, it is evident 

 that fish associated with the northern streams are subjected to heavier fish • 

 ine intensity than fish in the south. In 1950_,, it was estimated that 9ii..,271 

 anglers fished on Yellowstone Lake, (Moorej Cope, and Beckwith. 1952). The 

 figure for 195l was 163,3835 and for 1952, l87,oIi5. It is probable that 

 95^ of the angler effort was expended on the north end cf the lake, Tne 

 fishing pressure in the northern group is suspected to have been so intense 

 as to have caused the observed decline in fish length in Pelican and Arnica 

 Creeks. No reason is offered here for the increases in total length ob- 

 served on Chipmunk and Grouse Creeks. It seems likely that natural fluc- 

 tuations could account for these changes. 



Comparisons in fish length have been made between streams for the j^ear 

 1952, and summaries of results are presented in Table 1|, Grouse Creek had 

 the longest fish of any stream in which well=distributed samples were taken 

 from the spawning run. Grouse Creek fish had a mean Total length of 37U.7 

 nallimeters (IU.8 inches), while the smaller Yellowstone River spawners 

 measured at the Cascades, five miles downstream from Fishing Bridge, averaged 

 367.7 millimeters (lh.5 inches). Pelican Creek fish averaged 355.9 milli- 

 meters (lIi.O inches), and Arnica Creek fish averaged 3^3^3> millimeters (l3o9 

 inches). All comparisons showed si^^iificant differences except that between 

 Pelican Creek and Arnica Creek. Here a{;ain„ the smallest fish occurred in 

 those areas subjected to the heavy fisMng pressure^, suggesting a casual 

 relationship. 



THE FISHERY 



Total length measurements were recorded from the Yellowstone Lake 

 fisher;y' in 1950, 1951, and 1952 according to a plan that featured collec- 

 tion of data during the entire angling seasons. The plan not only assured 

 good sampling distribution from the standpoint of time, but permitted cer- 

 tain geographical subdivisions of the drainage to be considered separately. 



