Residence Times, Distribution, and Production of 

 Juvenile Chum Salmon, Oncorhynchus keta, in Netarts 



Bay, Oregon 



William G. Pearcy, Christopher D. Wilson, Alton W. Chung, and John W. Chapman 



ABSTRACT: Juvenile chum salmon resided in 

 Netarts Bay, a small, shallow estuary at the south- 

 ern spawning range of chum salmon in the North- 

 east Pacific, from mid-March until June during 

 each of three years from 1984 to 1986. Early in the 

 spring they were most abundant in beach seine 

 catches during high tide in the upper bay, indicat- 

 ing extensive intertidal excursions. Later in the 

 spring, when temperatures exceeded 14°-16°C in the 

 upper bay, they were most common in catches at 

 low tide in the lower bay. Based on recaptures of 

 fin-clipped hatchery fish, the residence of juveniles 

 varied inversely with size of fish at release. Large 

 (6.5 g) fish immediately emigrated from the estuary 

 and 3-i times as many returned as adult fish as LO 

 and 2.2 g juveniles, which had residence half-lives 

 of 5-16 days. Growth rates of juvenile chum salmon 

 during the 3 years were similar, but were low 

 (1.6-2.3% body weight/day) compared with other 

 studies. Production was also low. This may be 

 related to high metabolic costs at above optimal 

 temperatures and the large size of available prey in 

 Netarts Bay. 



The period of early marine residence is thought 

 to be a critical stage in the life history of Pacific 

 salmon, affecting the survival of young and the 

 numbers of adults returning in subsequent years 

 (Parker 1968; Peterman 1978; Pearcy 1984). The 

 period of estuarine residence may be especially 

 important for chum salmon, O^icorhynchiis keta, 

 (Healey 1982a; Simenstad and Wissmar 1984). 

 They enter estuaries at a small size and presum- 

 ably need to grow rapidly to avoid intense preda- 

 tion after they enter the ocean (Parker 1971; 

 Simenstad and Salo 1980; Healey 1982b; Simen- 

 stad and Wissmar 1984). The capacity of an 

 estuary to produce salmon may be hmited, how- 



William G. Pearcy, College of Oceanography, Oregon State 

 University, CorvalUs, OR 97331. 



Christopher D. Wilson, College of Oceanography, Oregon 

 State University, Corvallis, OR 97331; present address: 

 Department of Oceanography, University of Hawaii, Hono- 

 lulu, HI 96822. 



Alton W. Chung, College of Oceanography, Oregon State 

 University, CorvaUis, OR 97331. 



John W. Chapman, Hatfield Marine Science Center, New- 

 port, OR 9736.5. 



Manuscript Accepted March 1989. 

 Fishery Bulletin, U.S. 87: 553-568. 



ever, and the availability of prey resources may 

 affect salmon emigration, growth, abihty to 

 avoid predation, and thus survival (Reimers 

 1973 Bailey et al. 1975; Healey 1979, 1980a; 

 Sibert 1979; Simenstad and Salo 1980). 



The hypothesis that the estuarine phase of 

 the early life history of chum salmon is critical 

 needs to be tested (Simenstad and Wissmar 

 1984; Levings 1984). If this phase is essential, 

 increased releases of hatchery fish from private 

 or public hatcheries may not be beneficial unless 

 release strategies minimize or circumvent den- 

 sity-dependent growth and survival in estu- 

 aries, e.g., by modifying size, time, or numbers 

 offish released. Healey (1979, 1982a) concluded 

 that seaward migration was size dependent, and 

 loka (1978, unpubl. data) reported that large 

 (>8 g) juvenile chum salmon were capable of 

 migrating directly into offshore waters. This 

 suggests that estuarine rearing may not be 

 essential for chum salmon released from hatch- 

 eries at a large size. 



To evaluate the capacity of estuaries to pro- 

 duce chum salmon, we studied then- downstream 

 movement, distribution, abundance, residence 

 time, growth, and production in Netarts Bay, 

 OR. Netarts Bay is a small estuary along the 

 northern Oregon coast, near the southern distri- 

 bution of chum salmon along the coast of the 

 northeastern Pacific Ocean (Henry 1953). 

 Netarts Bay was selected for this study because 

 the Oregon State University chum salmon hatch- 

 ery (Lannan 1975, 1983) enabled experimental 

 releases of chum salmon at different times and 

 sizes, and because the residence times and 

 growth of chum salmon in a small estuary needed 

 to be compared with the results found in estu- 

 aries farther north. 



Netarts Bay (Fig. 1), located along the north- 

 em Oregon coast, has an area of only 10 km" at 

 mean high water (MHW). The bay is strongly 

 influenced by the ocean. Salinities generally ap- 

 proach ocean levels. The intertidal volume is 

 about 75% of the volume at MHW; 12% of the 

 Netarts Bay is subtidal (Glanzman et al. 1971; 



553 



