area criss-crossed with numerous shallow small channels. At Skeetercake 

 Creek, gravel removal in the upper mined area created an extensive backwater 

 which was utilized by adult Arctic grayling; at the middle mined area, bank 

 cover and pools were removed and this led to a reduction in the population 

 density of Arctic grayling. At the lower mined area of the Middle Fork 

 Koyukuk Ri ver-Upstream site, the single-channel sinuous configuration of the 

 river was changed to a split channel with extensive backwater areas. The 

 catch and species present were similar between mined and undisturbed areas, 

 but the age structure was more complex in the areas affected by gravel 

 removal. Age-0, age- I , and age-2+ Arctic grayling, age-0 round whitefish, 

 and age-l and adult longnose sucker were captured in the mined areas while 

 the species caught in undisturbed areas were primarily represented by a 

 single age group. Only round whitefish exhibited a more diverse age struc- 

 ture in the undisturbed areas. Similarly, at the Middle Fork Koyukuk River- 

 Downstream site the river was changed from a single channel to a multiple 

 channel braided system with numerous backwater areas. Arctic grayling domi- 

 nated the catch at the upstream area, but were replaced in the mined area by 

 round whitefish and slimy sculpin. 



Potential for Entrapment. Gravel removal in active floodplains created 

 areas of ponded water which were isolated from the active channel. Typically 

 these ponded areas were inundated during high water and became isolated as 

 the water level receded (Figures 51 and 52). Fish often entered these ponded 

 areas during high water and became stranded as the water level dropped. The 

 mortality rate of these fish was assumed to be high because they were sub- 

 jected to increased temperature, decreased dissolved oxygen, greater vulner- 

 ability to surface predation, desiccation if the area dried completely, and 

 freezing. There were 15 scraped areas at which ponded areas were observed: 

 Sinuk River, Washington Creek, Oregon Creek, Penny River, Nome River, 

 Ugnuravik River, Aufeis Creek, Kuparuk River, Skeetercake Creek, 

 Sagavan irktok River, Dietrich River-Downstream, Middle Fork Koyukuk River- 

 Upstream, and Middle Fork Koyukuk River-Downstream (Table 13). Sampling in 

 these ponded areas revealed significant entrapment at some sites. At Sinuk 

 River the mined area was not heavily utilized by fish. Pink and chum salmon 

 spawn in the river and considerable numbers of chum salmon fry were captured 



78 



