SAMPLING 



The experimental area (fig. 1) was about 

 8.0 km. upstream from Mayfield Dam, near 

 the Washington State Game Department Hatch- 

 ery at Mossyrock, Wash.; the reservoir at 

 this point is 219 m. wide and 30 m. deep. The 

 distribution of juvenile salmonids was sampled 

 with gill nets and a trawl. 



Equipment 



Gill nets were of monofilament nylon-- each 

 18.3 m. long, 3.7 m. deep, and "hung on the 

 half" (36.6 m. of netting on 18.3 m. of cork 

 line). Three 6.1-m. panels, of 2.2-cm., 2.9- 

 cm., and 3.5-cm. stretched measure, were 

 joined to form each net (fig. 2). Respective 

 strand sizes were 0.015 cm., 0.015 cm., and 

 0.02 cm. Each net was equipped with a lead 



Figure 2. — System for suspending gill nets in Mayfield Reservoir. 



line to make it hang properly and sufficient 

 flotation to make the buoyancy neutral. The nets 

 were marked and always set oriented in the 

 same direction to enable us to differentiate 

 between fish captured in the upstream and 

 downstream sides. 



Two rafts were anchored near the center 

 of the reservoir 18.3 m. apart. The opening 

 between the rafts facilitated boat passage. 

 Polypropylene hawsers, stretched from each 

 raft to the nearest shore at right angles to 

 the water flow, served as reference lines to 

 ensure that gill net sampling was always in 



the same cross section. The hawsers were 

 marked at 18. 3-m. intervals; a Styrofoam float 

 was attached at each mark, and a concrete 

 block was positioned directly below each 

 float. Each block was fitted with a pulley and 

 an endless nylon rope that extended from the 

 bottom to the surface. At the surface, each 

 loop was secured to a float. Half of each loop 



2 Trade names referred to in this publication do not 

 imply endorsement of commercial products by the Bureau 

 of Commercial Fisheries. 



