for L-ath of the five reaches (Table J). Flows less than the lower limit are 

 judged undesirable since they lead to substantial reductions of the standing 

 crops of adult trout or the standing crops of a particular group of adults, 

 sucli as trophy-size trout. Flows greater than the upper limit supported the 

 highest adult standing crops during the period estimates were made. Flows 

 bitwt'cn tlie lower and upper limits support intermediate standing crops or 

 those standing crops that normally occur within each reach. The lower limits 

 are selected as the flow recommendations. The reader is referred to Nelson 

 (1980a and 1980b) for a discussion of the trout standing crop and flow data 

 used to derive these recommendations and to Appendix A for a list of papers 

 pertaining to these standing crop estimates. 



3 



Table 1. Range of flow recommendations (m /s) derived from the trout standing 



crop and flow data for five reaches of the Madison, Beaverhead, 

 Gallatin and Big Hole Rivers. Recommendations apply to adult brown 

 and rainbow trout. 



3 

 Reac h Range of Flow Recommendations (m /s) 



Madison #1 

 Madison #3 

 Beaverhead #2 

 Gallatin //2 

 Big Hole #1 



a/ 



y 



c/ 



- Lower limit derived for age III rainbow trout. 



- Upper limit derived for age IV and older (trophy-size) brown and rainbow 

 trout . 



- Upper limit presently undefined. 



These recommendations are assumed to apply to all of the low flow or 

 non-runoff months even though they may have been derived from data pertaining 

 to only a portion of this period, such as the summer irrigation season. In 

 the headwaters of the Missouri River drainage of southwest Montana, the low 

 flow period generally includes the months of August through April. During 

 the high flow or snow runoff period, which generally occurs during May, June 

 and .luly, the MDFWP bases its recommendations on the high flows judged neces- 

 sary to maintain the channel morphology and to flush bottom sediments. This 

 methodology, which is referred to as the dominant discharge/channel morphology 

 concept, is described and the flow recommendations for each of the five reaches 

 during the high flow period are given in Montana Department of Fish and Game 

 (1979). High flow recommendations will not be discussed in this paper. 



Ttie final monthly recommendations for the low flow period along with the 

 median monthly flows of record are listed for each reach in Table 2. When 

 the recommendation exceeded the median monthly flow, the median monthly flow 

 became the final recommendation. Therefore, the monthly recommendations 

 listed in Table 2 are within the constraints of water availabilitv for a median 



