SW1MARY 



Length measurements of Yellowstone black-spotted trout (Salmo clarkl 

 lewisi ) have been recorded for spawners in various streams tributary to 

 Yellowstone Lake and in the lake fishery by Uo S„ Fish and Wildlife Service 

 personnel since 1936. Measurements were taken at frequent intervals from 

 19^0 to 19^2 J and resulted in several series of data suitable for statis- 

 tical comparisons o 



f4easurements made early in the program were in terms of standard 

 length, but most of the measurements in the study v/ere made on total 

 length. Fork length measurements were used in other phases of the program. 

 Measurements were taken to establish conversion factors^ and in the present 

 paper all lengths are expressed in terms of to^oal length. Conversion fac- 

 tors and a table of conversions are presented, A sexual dimorphism is seen 

 in the conversion factors. 



Comparisons between mean total lengths of various years have been made 

 for Pelican Creek, Chipmunk Creek^ Grouse Creekj and Arnica Creek. Signifi- 

 cant decreases in length have been measured in Pelican Creek and Grouse 

 Creek from 19$1 to 19^2 and in Arnica Creek from 19^0 to 19^1 and from 1951 

 to 19^2, Chipmunk Creek fish have shotm upward and downward trend? in mean 

 total length in the past few years. Streams tributary to the north end of 

 Yellowstone Lake appear to be affected to a greater extent than those enter- 

 ing the south end of the lake. 



Comparisons of mean total lengths of fish from streams in 1952 show 

 that of the streams in which good samples were securedj Grouse Creek fish 

 averaped the greatest length (37h.7 millimeters, lU. 5^' inches), which was 

 significantly greater than those of all other streams. Yellowstone River 

 spawners avera^.ed 367,7 millimeters (la, 5 inches), also sit^nlficantly dif- 

 ferent from all other streams. Differences between Pelican Creek fish^ at 

 355.9 millimeters (ih.O inches) and Arnica Creek fish, averaging 353.3 

 millimeters (13.9 inches) , were not significant, 



Conparisons of mean total lengths in major fishery areas of Yellowstone 

 Lake indicate that fish brought into Fishing Bridge area have decreased in 

 length each year from 1950 to 1952, Fish caught in the West Thumb area 

 decreased significantly from 195l to 1952_, and fish from the combined fish- 

 ery (all areas of the lake considered together) decreased in mean total 

 length from 195l to 1952. 



Comparisons between areas in the 1952 season show fish from the Fish- 

 ing Bridge area to be slightly larger (338 ol millimeters, 13^3 inches) 

 than fish from other areas, but si,,nificantly so only in relation to fish 

 from the West Thumb area, at 323.6 millimeters (12.7 inches). Fish from 

 the combined fishery averaged 336,5 millimeters (13.3 inches) in total 

 length, and those from Yellowstone River 330.6 aillimeters (13.0 inches). 



15 



