was marked at 3.7-m. intervals to indicate 

 depths of fishing. 



The endless ropes and the positioning of 

 the blocks made it possible to fish the gill 

 nets at any desired depth in the reservoir's 

 cross section. Spaces between floats con- 



stituted the fishing stations. The stations were 

 numbered 1 to 1 1 from the left (south) shore 

 to the right (north). 



Trawling was done to determine the dis- 

 tribution of small salmonids not vulnerable to 

 gill nets. The trawl (fig. 3) consisted of two 



Corkline 10.1 m. 



I 27cm. golw. pipe 



Figure 3. — Two-boat trawl used to sample distribution of juvenile salmonids in Mayfield Reservoir. 



wings, a belly, and a cod end. The wings and 

 belly were of 0.01-cm. knotted nylon twine, 

 2.2-cm. stretched measure; the cod end was 

 of 0.02-cm. knotless nylon twine, 1.27-cm. 

 stretched measure. 



The fish were wild downstream migrants of 

 the Cowlitz River system: coho salmon, Chi- 

 nook salmon (O. tshawytscha ). rainbow trout 

 ( Salmo gairdneri ), cutthroat trout (S. clarki) , 

 and squawfish ( Ptychocheilus oregonensis ). 



Conditions and Procedures 



The sampling varied with the abundance and 

 size of fish, availability of equipment, and 

 fluctuations in water velocity (table 1). The 

 stations fished during each of the four sampling 

 periods are shown in figure 4. Certain condi- 

 tions were constant throughout the experiment: 



1. Positions fished on any given day were 

 predetermined, but the order of the fishing 

 days within each sampling cycle was random- 

 ized. 



2. Minimum space between nets was 3.7 m. 

 vertically and 18.3 m. horizontally. 



3. Position 11 (fig. 1) was sampled each 

 operational day to note fish movement past 

 the experimental site. 



Trawls were towed 8 hours daily for 3 days 

 during each week of the 4th sampling period. 

 Times of sampling were varied (midnight to 

 8:00 a.m., 8:00 a.m. to 4:00 p.m., and 4:00 p.m. 

 to midnight) to include all hours of daylight 

 and darkness in each 3-day cycle; the order 

 of these fishing periods was randomized. Each 

 of the eight courses trawled was selected to 

 correspond with a portion of the reservoir 

 sampled with gill nets (fig. 5). 



