with a study evaluating "catch and release" angling on the 

 upper Madison River. Spring and fall estimates of trout stand- 

 ing crops by age-groups in a 415-mile portion of the closed >• \u ' 

 section have been made annually beginning in 1975. By fall 

 of 1978, following 19 months of closure, the estimated biomass 

 of trout in the 4Js-mile study section increased by 104%. At >. 

 this time the trout population was believed to be at or near 

 the carrying capacity. -' ^ 



Flows in reach #3, as measured at the USGS gage above 

 the mouth of the West Fork (Kirby Ranch) , were generally main- 

 tained at 700-1,500 cfs throughout the summer of 1978. The /v' 

 minimum flow recorded was 516 cfs. j. ■ '• . . - -.i j- :^ii 



Flows during 1979, a below average water year, were con- '"^ 

 siderably lower than those in 19 78. Flows were generally 

 maintained at 600-900 cfs throughout the sxommer of 1979. The 

 minimum flow recorded was 487 cfs. "j'^ 



Between September 1978 and September 1979, the estimated 

 biomass of adult trout (age 11+ and older) in the 4i5-mile 

 study section increased by 12% from 7,16 3 lbs to about 8,029 

 lbs. By species, the biomass of adult rainbow trout increased 

 by about 2 3% and that of brown trout decreased by about 4%. 

 If the assumption that the population in 1978 was at carrying ' 

 capacity is correct, then flows of about 600-900 cfs do not 

 appear to adversely affect standing crops of. adult trout in 

 reach #3. i' 



It is suspected that because of their above average size, 

 the recommendations previously derived for age 1+ brown trout 

 arfe probably more applicable to adults than to the juvenile '" 

 stage. During the study, age 1+ brown trout averaged 8.0 

 inches and 0.2 2 lbs. Until more conclusive data becomes 

 available, the recommendations derived for age 1+ brown trout " 

 will also be applied to adult brown and rainbow trout with one 

 minor adjustment. A minimum flow of about 650 cfs for adults 

 is judged more compatible with the standing crop and flow 

 data previously discussed for reach #3 than is the 650-750 cfs 

 derived for. age 1+ brown trout. 



Beaverhead River - Reach #2 --' '•''-■:-; =■ ^^ 

 ^— — ^^-^— — — ^— — — ^^— — __— — ^-^-^— — — — _ ^ 



The Beaverhead River provides the most complete set of 

 standing crop and flow data presently available to the Mon- ^ 

 tana Department of Fish, Wildlife and Parks. In the following 

 discussion, the data collected through 1978 are summarized. 

 A paper incorporating the 1979 data is presently being pre- 

 pared for publication in 19 80. 



33 



