The decreases may be due either to less available habitat or to competition 

 from species which more efficiently utilize the newly created habitats. 



The types of habitats present in a river are determined by the loca- 

 tion, size, configuration, and water quality characteristics of the river. 

 Features which define specific habitats include depth, velocity, substrate, 

 and cover. Alterations to a river which affect any of these features will 

 also affect the habitat available in the river and may impact habitats 

 downstream from the alterations. Habitat alterations may affect the quality 

 or diversity of the habitat, or both. Reduced habitat quality makes the area 

 less desirable to the species present prior to alteration, while altered 

 habitat diversity may favor one species or life history stage over another. 

 Reduced habitat quality implies alteration of a single habitat type whereas 

 reduced habitat diversity implies reduction in the number of available 

 habitats but the two responses are not independent. 



Several types of habitats may be used in the life cycle or even sea- 

 sonal cycle of an organism, and there is often a critical habitat which 

 controls the size of the population. In the arctic and subarctic environ- 

 ment, the critical habitat for fish populations is often the amount of 

 overwintering habitat. Other critical habitats often controlling fish popu- 

 lations are spawning and rearing areas. Critical habitats vary from stream 

 to stream and species to species depending on the characteristics of the 

 streams and the life cycle requirements of the species. 



Recent studies have been aimed at quantifying the effects of habitat 

 alteration on stream populations (Stalnaker and Arnette 1976, Bovee and 

 Cochnauer 1977, Binns and Eiserman 1979). Two of the basic requirements of 

 these efforts are detailed measurements of appropriate habitat parameters 

 and an intimate knowledge of the habitat requirements of the species in ques- 

 tion. The emphasis of the present study was on a multiple-disciplinary 

 survey of the effects of floodplain gravel removal on a broad geographical 

 scale. Because of the limited data on many species and complete lack of data 

 on many of the river systems studied, a detailed habitat analysis was not 

 possible. The 3 to 4 day surveys at each site allowed for gathering of basic 



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