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Causes of Winter Mortality 



Various studies have addressed the causes of winter 

 mortality in mountain streams. Maciolek and Needham (1952) 

 observed that heavy subsurface ice created dams, which 

 blocked the flow into side channels and caused a substantial 

 mortality of trout in Convict Creek, California. Ice, 

 slush, collapsing snow banks, and fluctuating flows 

 resulting from the periodic breakup of ice dams were 

 considered by Reimers (1957) to greatly influence winter 

 trout losses. Needham and Jones (1959) concluded that the 

 primary causes of winter mortality in higher elevation 

 streams exposed to severe weather conditions were: 



1. The sudden collapse of snow and ice into the water, 

 causing death by either direct crushing or suffocation 

 against the stream substrate, or both. 



2. The dewatering of sections of streams through the 

 creation of ice jams and snow and anchor ice dams, 

 resulting in the suffocation of fish. 



3. The sudden dewatering of flooded side channels or other 

 areas by the breakup and dispersal of ice and snow 

 dams, resulting in the suffocation of fish. 



