of fish collected (table 1) were coho salmon; 

 rainbow trout; cutthroat trout, S. clarki; 

 sculpins; largescale sucker, Catostomus ma- 

 crocheilus; and longnose dace, Rhinichthys 

 cataractae. Other species caught, but not con- 

 sidered to be predators, were the sand roller, 

 Percopsis transmontana; peamouth, Mylo- 

 eheilus caurinus; Pacific lamprey, Lampetra 

 tridentata; and western brook lamprey, L. 

 richardsoni. 



Chinook salmon fry were the most abundant 

 of the species observed throughout the lower 

 13 km. of the Elokomin River for 2 days after 

 each release. On the second day after each 

 release, fewer chinook salmon fry were ob- 

 served at km. 13 and 6.4 than on the previous 

 day; this observation suggested a downstream 

 movement. 



In 1963 we observed how chinook salmon 

 behave when they move downstream. On May 

 22 at 5:00 a.m., the morning after the release 

 at about 10:00 p.m. on May 21, chinook salmon 

 were abundant at km. 6.4; therefore, they had 

 moved downstream in the dark. On the same 

 day at 7:00 a.m. at km. 3.2, schools of 5 to 30 

 chinook salmon each were seen drifting down- 

 stream tail first near the midstream surface 

 in a riffle. The salmon passed km. 3.2 at an 

 estimated rate of 200 to 300 per min. at 11:00 

 a.m. on May 22 and 100 per min. at 11:00 a.m. 

 on May 23. No downstream movement was 

 noted at km. 3.2 on May 24, but schools of 

 salmon descended the river in the afternoon 

 of May 24 at km. 2. A few were seen moving 

 downstream at km. 3.2 the morning after the 

 May 27 release; none were seen there on May 

 29. At any one time after the three releases, 

 not all chinook salmon were moving down- 

 stream; some were observed maintaining their 

 positions in low-velocity water. 



Trout, yearling coho salmon, and sculpins 

 are known to eat salmon fry. These predators 

 were abundant in the study area. Rainbow 

 trout were more abundant than cutthroat trout, 

 but both species were relatively scarce in the 

 lower 16 km. of the river. In 1963 trout were 

 most abundant at km. 3.2 probably because 

 of releases from a trout hatchery near km. 4.8. 

 Coho salmon fry and yearlings were abundant 

 throughout the lower 16 km. of the river. 

 Sculpins were distributed through the study 



Reticulate sculpin 



Torrent sculpin 



2 3.2 



6.4 13 16 



Kilometers From Mouth of River 



Figure 1.— Average numbers of four species of sculpin 

 collected at five points in the lower 16 km. of the 

 Elokomin River, 1962-63. 



area and were the most abundant wild fish. The 

 average number of sculpins collected at a site 

 where sampling efforts were similar indicates 

 differences in species distribution in the lower 

 16 km. of the river (fig. 1). 



Six species of fish not known to prey on 

 salmon fry were collected from the study area. 

 Longnose dace were abundant in riffles from 

 km. 3.2 to 13. Adult largescale suckers, which 

 ascended the river to spawn, were observed 

 during 1962. Many Pacific lampreys and 

 smaller numbers of western brook lampreys 

 spawned in the lower 13 km. in 1962 and 1963. 

 One sand roller and one peamouth were taken 

 at km. 2 in 1963. 



The environmental niche occupied by 

 salmon and trout, determined by underwater 

 observation, appeared to be more a function 

 of fish size than any other single observable 

 factor. Coho salmon fry, 32 to 60 mm. long, 

 were most common in water 1 to 10 cm. deep. 

 Coho salmon and rainbow trout yearlings, 80 

 to 120 mm. long, were intermixed at depths 

 greater than 18 cm. Rainbow and cutthroat 

 trout over 130 mm. long were usually in water 

 deeper than 40 cm. Salmon and trout were 

 not observed in high-velocity riffles, except for 

 chinook salmon that were actively migrating 



