above and below the mined area. Pink and chum salmon are often associated 

 with low velocity water and there was high potential for entrapment of 

 downstream migrants of these two species. The same two species, plus coho 

 salmon, were vulnerable to entrapment at the Penny River site. At Washington 

 Creek, Oregon Creek, and Penny River, the dominant species, Arctic char, are 

 probably not greatly affected by entrapment because they are generally 

 associated with high velocity water and instream cover and would tend to 

 avoid the type of areas which are prone to ponding. At the Kuparuk River 

 site, a natural ponded area, apparently enlarged by gravel excavation, 

 contained a high density of age-l Arctic grayling (Table 21, Figure 51). At 

 the latter site both natural and ponded areas created by gravel removal were 

 present in the study reach. At the Middle Fork Koyukuk R i ver-Upstream, 

 considerable stranding was documented when several isolated pools were 

 sampled (Table 21, Figure 52). The primary species subjected to entrapment 

 in the Middle Fork Koyukuk River system was Arctic grayling. 



Migration Blockage. Two types of potential mi n i ng- i nduced migration 

 blockages were observed during the study: (I) blockage due to aufeis for- 

 mation, and (2) blockage due to lack of surface flow. Possible temporary 

 migration blockage due to aufeis formation may have occurred at the Wash- 

 ington Creek and Oregon Creek sites (Figure 53). The principal migrations 

 that could be affected in these particular systems would be upstream and 

 downstream movements of juvenile Arctic char and juvenile coho salmon moving 

 from overwintering areas to feeding areas and downstream migrations of adult 

 Arctic char returning to the sea from upstream overwintering areas, if 

 present. A short-term delay in these migrations may not have a critical 

 effect on these particular species, but a similar blockage for another 

 species, such as an upstream spawning migration of Arctic grayling, may have 

 a great effect on the population in the river. A blockage due to lack of 

 surface flow can occur where flow is spread over a wide area and there is 

 considerable intergravel flow. Under such conditions, all surface flow may 

 cease. Such a condition occurred at the Aufeis Creek site (Woodward-Clyde 

 Consultants 1976) (Figure 54) and possibly could occur at the Nome River 

 site (K. Tarbox, personal communication). The potential for such a blockage 



180 



