1962 and 1963 and in Herman Creek in 1962. 

 The data include the percentage of sculpins 

 that ate salmon, the average number of salmon 

 per sculpin, specific differences among sculpins 

 as predators of salmon, and the comparative 

 mortalities of salmon reared on wet diets and 

 fortified diets. 



MATERIALS AND METHODS 



Elokomin River 



Predation on hatchery chinook salmon was 

 studied principally in the lower 13 km. of the 

 Elokomin River (Wahkiakum County, Wash.), 

 which empties into the Columbia River about 

 56 km. from the Pacific Ocean. The mean 

 flows of the Elokomin River 2 km. above the 

 mouth in May 1962 was 7.4 c.m.s. (cubic meters 

 per second) and in 1963 was 6.3 c.m.s. The 

 Elokomin River consists generally of riffles; 

 it has moderate velocities over a rocky bottom 

 and occasional pools, up to 91 m. long. Below 

 km. 2, the river is influenced by tides and flow 

 is reduced. The water was clear except for 

 turbidity on May 22, 1963. 



The diet of salmon reared in the Elokomin 

 River Hatchery differed between the 1961 and 

 1962 brood years: the 1961 brood was fed 

 beef liver, beef spleen, turbots, pasteurized 

 salmon viscera, pasteurized salmon carcasses, 

 and herring meal; the 1962 brood was fed 

 the same diet for 6 weeks and then fed Oregon 

 moist pellets (Hublou, 1963) for about 8 weeks. 



At the time of release, the 1961 brood aver- 

 aged 59 mm. fork length (range, 40-80 mm.) 

 and averaged 469 salmon per kilogram; the 

 1962 brood averaged 60.1 mm. fork length 

 (range, 38-79 mm.) and averaged 447 salmon 

 per kilogram. 



All fry were released into the Elokomin 

 River after darkness. The 1961 brood, esti- 

 mated at 1,493,000 fry by hatchery personnel, 

 was released on May 24, 1962; the 1962 brood 

 was released in three groups in May 1963 — 

 841,000 on May 21, 1,394,000 on May 22, and 

 127,000 on May 27. The group liberated on 

 May 27 had been retained for treatment of 

 disease, and I assumed these to have been of 

 quality equal to the other released fish. The 

 May 21 and 22 plantings were designated as 



the 1963A release; the May 27 release, as the 

 1963B. 



Possible predators were collected by electro- 

 fishing (Patten and Gillaspie, 1966) at various 

 times and locations in the Elokomin River. We 

 also observed the movement, habitat, and be- 

 havior of prey and predators. In collecting, 

 we moved upstream to avoid the capture of 

 predators that might have consumed electro- 

 narcotized salmon fry which had drifted down- 

 stream. All sculpins 50 mm. or longer were 

 retained. 



Table 1 shows times and locations of sam- 

 pling. We collected predators in the Elokomin 

 River for 2 successive days after each release 

 (extended to 3 days for the 1963 A release 

 made on May 21 and 22). A collection was 

 made at 5:00 a.m. at km. 6.4 (designated 6.4A 

 in the tables) on May 22, 1963, to determine if 

 salmon released the previous evening had been 

 preyed upon during darkness. Collections were 

 made in the absence of released chinook salmon 

 at km. 2.3 and 6.4 on May 21, 1963 (table 1), 

 and at km. 16 on May 21 and 22, 1963 (table 1) , 

 to find the intensity of predation on wild coho 

 salmon, O. kisutch. 



Herman Creek 



Predation on hatchery chinook salmon was 

 studied secondarily on fish released into Her- 

 man Creek 0.2 km. from the Columbia River at 

 Oxbow Hatchery, 6.4 km. above Bonneville 

 Dam in Oregon. The chinook salmon were 

 released into a diverted channel of Herman 

 Creek, which enters the Columbia River 

 through a 200-m. outlet channel about 23 to 

 46 m. wide and 4 m. deep. The water was 

 clear, and velocity was negligib'e except at 

 the diversion inlet. 



The diet of chinook salmon reared at Ox- 

 bow Hatchery consisted of beef liver (20 per- 

 cent), hog liver (20 percent), tuna viscera (10 

 percent), beef spleen (10 percent), and pas- 

 teurized salmon viscera (40 percent). The 

 salmon had a mean fork length of 56.8 mm. 

 (range, 45-64 mm.) at the time of release, 

 and numbered 427 to the kilogram. The re- 

 lease totaled about 2.3 million fish and started 

 at 9:00 p.m. on May 16, 1962, and was com- 

 pleted during darkness. 



