Effects on Overwintering Areas 



Possible effects of gravel removal on fish overwintering areas were 

 observed at several of the study areas. Potential overwintering areas were 

 created at the deep pit sites — Dietrich R i ver-Upstream, West Fork Tolovana 

 River, Tanana River-Downstream, and Tanana R i ver-Upstream — by the pits 

 themselves. The Dietrich R i ver-Upstream pit has been reported as an over- 

 wintering area (W. Anderson, personal communication to A. Ott). In addition, 

 outflow from the West Fork Tolovana River pit created a potential overwinter- 

 ing area approximately 50 m downstream from the outlet where a deep natural 

 pool with a 1-2 cm ice cover existed into March 1979. A possible overwinter- 

 ing area on the Penny River was altered as a spring-fed tributary; Willow 

 Creek, that had previously entered the main channel at a deep pool, now 

 entered the river through the scraped area in a series of shal low braided 

 channels (Figure 58). 



The pattern of freezing observed during winter studies on six of the 

 pit sites indicated that fish entrapment was not a problem during the 1978- 

 1979 winter (Table 24). In those pits studied, the outlet remained open 

 well intowinter with outlet flow velocities increasing as the still water 

 at the edges of the pit froze, reducing the volume of the pit. Fish appeared 

 to move to the open water found at the outlet areas and the increased veloc- 

 ities may have induced the fish to move downstream to areas of reduced 

 velocity. If fish were holding at an outlet pool and the outlet closed 

 downstream from the holding fish, entrapment could occur. The outlet area in 

 the pits examined was general ly quite sma I I. However, the number of fish 

 affected compared to the numbers using the pit in the summer would be mini- 

 ma I . 



The outlets of the Prospect Creek and Jim River sites remained open at 

 least until late January and possibly into early February, thus fish had 

 ample opportunity to emigrate as flow decreased during freeze-up. Fish were 

 present (caught and observed) at both sites in early November but were not 

 evident in late January. Both sites were frozen to the bottom in March. At 

 the Penny River pit site, fish were caught in the pit in late December and 



