The Uo S. Fish and Wildlife Service and its predecessor^ the Uo S. 

 Bureau of Fisheries j has conducted biological studies of the Yeiicwstone 

 black-spotted trout ( Salmo clarid lewisi ) on Yellowstone Lake and its 

 tributaries since 1936. Prior to that year, considerable knowledge per- 

 taining to the biology, culture^ and life history of this species had 

 been secured through the efforts of U, S, Fishery Station personnel en- 

 gaged in egg ■= taking operations in these waters o The 1936 beginnings of 

 organized investigations into the habits of the Yellowstone black^spot+ed 

 trout in its native waters took the form of surveys and collection of bio- 

 logical data by Dr. Leonard Schultz and Mr» Richard Foster. Mr. Foster 

 continued the biological work in 1937j and Mro Marion Madsen conducted 

 investigations in 1938 and 1939 » In 19i|2 5 and for three years thereafter, 

 Dro Stillman Wright supervised Yellowstone studies on this species, and 

 was able to secure more extensive data than had been available to the 

 earlier workers,, Dr. Wright and his assistants inaugurated a system for 

 systematically counting and measuring spawners in key streams, and gathered 

 much other morpho metric data over a period of a few years » Most of this 

 work was deemphasized toward the end of the war, but hatchery personnel con- 

 tinued the sequence of some phases of the xrork., 



In 19^0, intensive studies were undertaken to cover several aspects 

 of the fishery problem on Yellowstone Lake, arid many features of the earlier 

 programs were revived. Most of the studies were attacked on larger scales 

 than previously. The 1950 investigations were continued in 19$1 and 1952. 



This paper pertains to lengths of fish handled during the progress of 

 the various investigations « This information is deemed important chiefly 

 because of the value of year-to-year changes in lengths of fish as a basis 

 for recognition of critical alterations in the composition of populations. 

 Such trends, especially when viewed in connection with other changes occur- 

 ing in the fishery, often supply weighty evidence of population improvement 

 or decline. Reliable measurements of length also help in the recognition 

 of separate populations that may exist in the same or connected bodies of 

 water. 



The purpose of these studies and this report has been to assemble all 

 known information on lengths of black-spotted trout in Yellowstone Lake for 

 critical examination and comparison. Comparisons have been made between 

 differences in mean total length from year to year and from place to place 

 within the drainage. Information on trends is essential as a part of the 

 general investigative program leading toward recommendations pertaining 

 to the regulation of the Lake Yellowstone fishery. 



METHODS 



Field methods used in this study have consisted of measuring adult 

 fish on measuring boards. The metric system has been used by all workers. 



