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60 percent over four years in Convict Creek, a small stream 

 in the Sierra Nevada Mountains of California. Winter losses 

 of the larger trout (four inches and longer) were higher, 

 ranging from 48 to 91 percent and averaging 80 percent over 

 four years. 



In Montana, there is little quantitative data documenting 

 the winter trout mortality that occurs in mountain streams. 

 Mortality data, however, are available for study sections of 

 the upper Gallatin and upper Madison rivers (Table 1). The 

 physical environment of these rivers, like mountain streams, 

 is also affected by icing and other harsh winter conditions. 

 Even though the trout in these rivers are subject to angler 

 related mortalities in summer, the winter mortality rates 

 usually exceed those during the warmer months, a fact 

 attributable to the severity of the winter environment. 



Evidence of elevated mortalities in winter indicates that 

 the winter environment ultimately limits the numbers and 

 pounds of trout that can be maintained indefinitely by the 

 aquatic habitat of high elevation streams. Severe winter 

 conditions appear to affect all age-groups of trout, 

 although Stalnaker and Milhous (1983) consider the 

 overwinter losses of young-of-the-year trout to be most 

 limiting to the population. 



