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during the anchor ice cycles. The combination of harsh 

 weather conditions and the naturally occurring low flows can 

 severely reduce the food supply in some years, potentially 

 affecting trout survival during the winter and in subsequent 

 months as well. Winter flow depletions have the potential 

 to reduce the food supply even further. 



The eggs of several species of salmonids (brook trout, brown 

 trout, bull trout, kokanee salmon and mountain whitefish) 

 are deposited in the gravels of mountain streams during the 

 fall. Incubation of these eggs proceeds slowly during the 

 winter months due to low water temperatures, and the fry 

 typically emerge from the gravels during early spring. 

 During the winter incubation period these eggs are 

 susceptible to mechanical destruction resulting from ice 

 scour as well as mortality caused by freezing and 

 dessication. Winter flow depletions have the potential to 

 aggravate the above causes of egg mortality. 



When considering the severity of the winter environment and 

 its impact on trout and other aquatic life, a prudent 

 approach for deriving instream flow recommendations for 

 Montana 'a unregulated mountain streams is to prohibit winter 

 (approximately November through March) flow depletions 

 altogether. Until studies of the winter flow needs of trout 

 can prove otherwise, a policy of no winter depletions is 

 advisable if the goal is to maintain the trout populations 



