only at infrequent h i gti water levels. The Dietrich Ri ver-Upstream pit, 

 however, was connected to the active channels but fish were apparently not 

 utilizing the pit for feeding. Benthic macro! nvertebrate densities in both 

 these pits were low when compared, to those of other pits. The spring-fed 

 channels upstream from the Dietrich River pit were utilized by adult Arctic 

 grayling and the pit itself was reported to be an overwintering area. All 

 other pits were highly productive and heavily utilized by fish as summer 

 rearing areas. The shallow pits. Penny River, Prospect Creek, and Jim River 

 side channel (this site had some characteristics of a pit) supported high 

 densities of juvenile salmon (coho in the Penny River, chinook in the latter 

 two) as well as some species associated with both a lacustrine environment 

 (Alaska blackfish, burbot, northern pike) and stream environment (round 

 whitefish, Arctic grayling, slimy sculpin). The productive Southern Interior 

 deep pits. West Fork Tolovana River and two Tanana R i ver-Upstream, contained 

 a more lacustrine fish fauna with northern pike dominating the fauna and 

 humpback whitefish, least cisco, and burbot also present in the Tanana 

 R i ver-Upstream complex. 



Potential for Winter Mortality and Winter Survival Areas 



The creation of shallow pits and subsequent heavy summer usage by fish 

 created the possibility for entrapment during freezeup and subsequent winter 

 mortality when the pit freezes solid or decay of vegetation consumes the 

 dissolved oxygen. The pattern of freezing observed during winter studies 

 indicated that during the year of observation, entrapment was minimal and 

 probably not a significant problem. 



The creation of deep pits connected to the river could create over- 

 wintering areas; this was documented or suggested at several study sites. 

 All pits studied, with the exception of Tanana River-Downstream, however, 

 had a mean depth insufficient to preclude winter mortality. Intergravel flow 

 appeared to maintain the ability of some pits to support winter fish sur- 

 vival, but this is an unpredictable factor in the design of pits. 



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