FISHERY BULLETIN: VOL. 81, NO. 4 



• Beach Seine 

 O Purse Seine 



Pacific 

 Ocean 



FIGURE 1.— Sampling sites in the upper and lower areas of the Columbia River estuary. 



ing upon distance from the river mouth, river flow, 

 and tidal stage. Saline water penetrates along the 

 river channels into sections of the upper estuary at 

 times; however, in most instances, our sampling was 

 associated with fresh water. Habitats we called inter- 

 tidal often consisted of both intertidal and some sub- 

 tidal areas. 



Sampling 



Two beach seines were used to sample in intertidal 

 areas. The seines were 50 m long; one was 4.0 m and 

 the other 3.4 m deep at their deepest points. Both 

 nets contained panels with the following mesh sizes 

 (stretched): 19.0, 12.7, and 9.5 mm. Knotless mesh 

 was used in the bunt to minimize scaling of fish (this 

 was also true in the purse seine). The fishing method 

 was similar to that described by Sims and Johnsen 

 (1974). Beach seining was done at various tide 

 stages. 



A 200 m long by 9.8 m deep purse seine was em- 

 ployed to collect pelagic species. Mesh sizes 

 (stretched) in the seine included 19.0 and 12.7 mm. 

 Purse seine sets were made for 5 min in an up- 

 stream direction during various stages of the 

 tide. 



Collapsible hoop nets and trawl nets were also used, 

 but captured comparatively few salmonids. 



Monthly sampling throughout the estuary was per- 

 formed from February 1980 through January 1981. 

 The effort involved 11 beach seine and 16 purse 

 seine sites (Fig. 1). Five intertidal sampling stations 



(beach seine) were in the upper estuary and six in the 

 lower. Eight of the pelagic sampling sites (purse 

 seine) were in the upper estuary and eight in the 

 lower. Before each sampling effort, water tempera- 

 ture, conductivity, and salinity were recorded using a 

 Beckman, 2 Model RS5-3 salinometer and probe. 



Fish were identified and enumerated, and a random 

 subsample of up to 50 fish of each species or stock 

 was measured to the nearest millimeter (total length) 

 and weighed to the nearest gram. Subyearling and 

 yearling chinook salmon were separated using 

 length-frequency histograms. The number and total 

 weight were recorded for those species with over 50 

 individuals in a single sample effort. 



A representative subsample of five individuals of 

 each species was selected from each purse seine and 

 beach seine set for stomach analysis. Fish taken for 

 stomach analysis were injected with a 20% buffered 

 Formalin solution soon after capture to preserve 

 stomach contents. Injected fish were weighed and 

 measured at the laboratory. Stomachs were then 

 removed from the fish and placed in vials containing 

 70% ethyl alcohol. 



Fish stomach contents were examined in a watch 

 glass using a 10X binocular dissecting microscope. 

 Food organisms were identified to the lowest practi- 

 cal taxon and weighed to the nearest 0.0001 g after 

 blotting and air drying for 10 min. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



816 



