tion of the pool-riffle frequency, and (2) increased braiding characteris- 

 tics with the associated loss of bank cover and altered flow regime. 



At the Kavik River site, habitat quality was altered by the erosion of 

 berms left in and along active channels, channelizing one section of the 

 river, and creation of a more braided configuration. The densities of Arctic 

 char and Arctic grayling for each study area were estimated by repeated 

 shocking of blocked channels (Table 17). Total fish densities in the mined 

 area were reduced by a factor of three or greater when compared to the 

 undisturbed areas (Table 18). The catch of adult Arctic grayling, as de- 

 termined by angling, was also lower in the mined area (Table 19). The den- 

 sity reductions occurred in both Arctic grayling and Arctic char with 

 neither species apparently favored by the habitat alteration. Removal of 

 instream cover appeared to be a major habitat alteration affecting reduction 

 of fish densities because a channel that contained boulders adjacent to the 

 mined area supported densities of both species comparable to those in un- 

 disturbed areas. 



Species and Age Group Alteration. Species shifts were observed at nine 

 sites (Washington Creek, Oregon Creek, Penny River, Kuparuk River, 

 Sagavan i r k tok River, Ivishak River, Dietrich River-Downstream, Middle Fork 

 Koyukuk R i ver-Upstream, and Middle Fork Koyukuk River-Downstream) because 

 alterations in the type of habitat allowed other species to populate an area 

 (Table 20). A similar response is a change in the age structure of fish 

 inhabiting a reach of river, as was observed at Kuparuk River, Skeetercake 

 Creek, and Middle Fork Koyukuk Ri ver-Upstream. In these areas newly created 

 habitats favored or excluded certain age groups in the areas affected by 

 gravel removal operations. On Kuparuk River, the mined area had a more 

 uniform habitat than the upstream area and numerous small channels of simi- 

 lar velocity. Age-0 and age-l Arctic grayling and several age groups of 

 slimy sculpin were present in the upstream area while only age-l Arctic 

 grayling were captured in the mined area. At the Sagavan i rk tok River, Arctic 

 grayling juveniles were confined almost exclusively to the mined area, while 

 the upstream area catch was dominated by round whitefish and an unmined 

 channel adjacent to the mined area contained adult (-300 mm) Arctic gray- 

 ling. Again, the mined area was changed from a large single channel to an 



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