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observed that the highest standing crops of aquatic food 

 organisms occurred in summer rather than in the winter. The 

 conflicting results were attributed to the severity of the 

 weather. Reimers' study was conducted during average and 

 extremely severe winters while the results of Maciolek and 

 Needham were obtained in a mild winter. During the average 

 and severe winters, repeated anchor ice formation resulted 

 in sudden releases of water which scoured the stream bottom 

 and dislodged the bottom organisms. Ice and slush dams 

 formed by the accumulation of released anchor ice further 

 depleted the food organisms by exposing the bottom habitat 

 to partial drying, freezing and rewatering. The end result 

 was a gradual depletion of the food organisms through the 

 winter. 



These results indicate that the populations of semi-aquatic 

 insects in high elevation streams can be reduced during a 

 typical winter. Given the severity of most winters in the 

 mountain regions of Montana, the depletion of food organisms 

 in winter and early spring is likely a common event. 



Feeding and Digestion in Winter 



Trout in mountain streams are reported to feed regularly in 

 winter whenever drifting food organisms are available. The 

 daily breakup of anchor ice in Sagehen Creek, a small stream 

 in the Sierra Nevada Mountains of California, dislodged 



