EXPERIMENTAL PROCEDURES 



Hydrological features and fish fauna of the 

 Yakima River were examined fronn April 8, 

 1957, to May 20, 1958. Seven sampling trips 

 were made at 2-month intervals to collect 

 data at about every 8 km. along the river 

 (fig. 1). Thirty- six sampling sites were pre- 

 determined from aerial photographs, but one 

 site (km. 80) was not accessible and was not 

 fished. A complete trip from Easton to the 

 mouth of the river usually took 20 days. The 

 schedule was interrupted on the first trip 

 (April 8 to June 20, 1957) by flooding, which 

 extended the time to over 2 months and pre- 

 vented sampling at sites at km. 105 and 281. 



We used electrofishing gear to collect fish at 

 each site. Collections made on a trip represent 

 an instantaneous sample, and we assume that 

 catches at a site represent the species within 

 an 8-km. section of the river. 



The "Type I electric shocker" (Patten and 

 Gillaspie, 1966) was used on the first trip; 

 the more effective "Type 11 shocker" (Dale, 

 1959), on other trips. We tried to sample 

 different ecological areas for representative 

 populations at each site. Wading and floating 

 techniques were used. The wading method was 

 effective for collecting small fish that prefer 

 shallows at the stream edge, especially in 

 areas of cover. The floating method, used in 

 deep or swift waters, accounted for most fish 



Figure 1. — Sampling sites along the main stem (lower 281 km.) of the Yakima River, by distance (km.) from 



the mouth of the river. 



