INTRODUCTION 



The literature contains little information concerning the 

 instream flow methods that can be applied to mountain 

 streams to determine the amount of flow that is needed 

 during the winter months to sustain the existing wild trout 

 populations. Due to the lack of published methods, the 

 Montana Department of Fish, Wildlife and Parks (MDFWP) has 

 developed its own policy regarding winter flow depletions. 

 This policy is based on biological considerations reported 

 in the literature and the physical characteristics of 

 Montana's trout streams in winter. 



The purpose of this paper is to briefly review the 

 literature pertaining to trout streams in winter and present 

 arguments in support of the present instream flow policy of 

 the MDFWP. 



LITERATURE REVIEW 

 Trout Mortalities in Winter 



It is well accepted that substantial losses of wild trout 

 can occur in winter, particularily in mountain streams that 

 are subject to icing and other harsh weather conditions. 

 Needham et al (1945) reported that the overwinter losses of 

 all brown trout ranged from 26 to 85 percent and averaged 



