EFFECTS OF HABITAT ALTERATION ON FISH POPULATIONS 



Observed Alteration of Summer Distributions or Densities 



Several types of changes in summer fish distribution were observed 

 in the mined areas; specific types of distributional changes were related to 



certain types of habitat alterations caused by gravel removal. These changes 

 included: (I) reduction in the numbers of all fishes in a disturbed area, 

 (2) replacement of one species by another species, (3) replacement of one 



age group by another age group, and (4) increase in the number of fish or 



species, or both (Table 15). A list of all species caught during the study 



and their scientific names is included in Appendix A. 



Density Reductions. Reductions in numbers of all fish populations 

 occurred at Washington Creek, Aufeis Creek, and Kavik River sites. The 

 habitat in the upper mined area of Washington Creek was altered in several 

 ways, reducing habitat quality and diversity to an extent that few organisms 

 could utilize the newly created habitat. The density and biomass of Arctic 

 char was significantly reduced downstream of the upstream sample area (Table 

 16). The slimy sculpin density and biomass was also reduced in the upper 

 mined area, but increased in the lower sample areas to densities exceeding 

 those in the upstream area. The sculpin biomass remained low, indicating the 

 slimy sculpin captured below the mined area were smaller than those captured 

 above. Thus, there was a replacement of Arctic char habitat by a habitat 

 more suitable for slimy sculpin in the lower three sample areas. The spe- 

 cific habitat alterations that led to a loss of Arctic char habitat were 

 removal of bank and instream cover and possibly reduced water quality (i.e., 

 increased turbidity) caused by siltation from the melting aufeis field. 



At the Aufeis Creek site, there was only one life history stage of 

 Arctic grayling present during each sampling trip, thus any changes would 

 have to be density reductions rather than species or age-group shifts. 

 Density reductions were recorded in the upper mined area during the first 

 trip and al I disturbed areas in the second trip. Specific habitat altera- 

 tions that led to reductions in Arctic grayling habitat were: (I) the reduc- 



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