70 



Fishery Bulletin 89(1), 199) 



Cross section 



Rock 

 cliff 



OREGON 



1 

 I I I I 



Kilometers 



Figure 1 



Jones Beach sampling site. Beach and purse seining areas are denoted by the two asterisks on the cross section. 



seining was on the south shoreline, lateral to the purse 

 seine site (Fig. 1). 



Conditions of the Columbia River were different dur- 

 ing each sampling period. River flows ranged from 

 6800 to 7600 m 3 /second (U.S. Army Corps of Engi- 

 neers 1978-80). Turbidity and water temperatures 

 ranged from 5 to 11 Jackson Turbidity Units and 12° 

 to 17°C, respectively. Tides at Jones Beach are semi- 

 diurnal (~7 hours of ebb and 4.5 hours of flood current); 

 flow reversal occurs during flood tides throughout most 

 of the year. River flows in the range of 5000-12,000 

 m 3 /second generally occur during the period May 

 through mid-July, and flood tide effects are diminished 

 at these high flows. 



Captured salmonids were anesthetized, identified to 

 species, and enumerated (Dawley et al. 1985). Subyear- 

 ling and yearling chinook salmon were separated on 



the basis of fork length; separation points were deter- 

 mined from the bimodal curves of length frequency. 

 Verification of age from marked fish of known age 

 (4.8-6.5% of catch) showed about 4% error in separa- 

 tion. All captured fish were either held in tanks onshore 

 until sampling was complete and then released or 

 transported downstream from the sampling area and 

 released. 



Beach seining 



The beach seine was 95 m long by 5 m deep with 1-2 cm 

 (stretch) webbing (Sims and Johnsen 1974). The net 

 was fished downstream regardless of tidal influence. 

 An anchor was used to secure one end of the net on- 

 shore and the opposite end, containing the bunt, was 

 towed upstream at the 1-m depth contour, then arched 



