53 



Growth of Trout (Hildreth Section) 



Mean weights by age group of brown trout in the spring and rainbow 

 trout in the fall are given in Table 18. Mean weights of all age groups 

 are exceptional compared to most other rivers in Montana. The growth of 

 trout in the Big Horn River, another tailwater fishery, is similar to 

 that in the Hildreth Section of the Beaverhead River (Stevenson, 1975). 

 Mean weights of age II and older brown trout in the fall and age II and 

 older rainbow trout in the spring are considered biased due to the move- 

 ment of nonresident spawning fish into the Hildreth Section. 



Since growth-flow relationships for any age group of trout could 

 not be demonstrated, the influence of densities on growth was investigated, 

 Mean weights of age II brown trout in the spring appear density related 

 (Figure 13). The estimated numbers of age II brown trout explain 66% 

 of the annual variation in the mean weights of age II brown trout. 

 Density-growth relationships were not demonstrated for any other age 

 group of trout. 



Trout-Flow Relationships in All Sections 



During the Spring of 1975 and 1976, numbers and biomass of trout 

 were estimated in a series of sections in the Beaverhead River (Appendix 

 Tables 19 and 20). In the spring of 1976, two sections, Grant (0.1) 

 and Pipeorgan Extended (8), were added. Estimates in 1975 were made 

 between March 6 and April 14 and in 1976 between March 10 and May 20. 

 Except for Grant (0.1), brown trout was the dominant species of trout 

 in the sections. The cause of the resurgence of rainbow trout numbers 

 in the Wheat (27) and Westside Canal (29) Sections is unknown. Spring 

 creeks in this area may be providing spawning habitat and recruits. 



