Abstract.- Peak beach-seine 

 i-atclies o( small (60-120 mm FL) 

 juvenile fall chinook salmon in Coos 

 Bay occurred about 30-45 days after 

 peak seine catches farther upstream 

 in the Coos and Millacoma Rivers. 

 The average time between release 

 and capture in the bay of marked 

 hatchery fall chinook salmon was 

 about 30 days, but ranged up to 83 

 days. Thus, many small hatchery and 

 wild fall chinook salmon remained in 

 Coos Bay for about 1 month befoi'e 

 entering the ocean. Most captures of 

 large (123-156 mm mean FL) tagged 

 spring chinook salmon released di- 

 rectly into the bay occurred within 

 10 days following release, indicating 

 a shorter period of residence in the 

 bay for spring chinook salmon than 

 for fall chinook salmon. Catches of 

 juvenile spring chinook salmon were 

 very patchy. Potential for competi- 

 tion between juvenile fall and spring 

 chinook salmon in Coos Bay may be 

 reduced l.)ecause of diffei'ences in the 

 timing and locations of maximum 

 abundance of these two groups. Fin- 

 clipped fall chinook salmon grew at 

 least 0.2-0.5 mm per day. 



Distribution and Residence Times of 

 Juvenile Fall and Spnng Chinook 

 Salmon in Coos Bay, Oregon 



Joseph P. Fisher 

 William G. Pearcy 



College of Oceanography, Oregon State University 

 Corvallis, Oregon 97331 



Manuscript accepted 31 July 1989. 

 Fishery Bulletin, U.S. 88:51-58. 



Estuaries are important rearing habi- 

 tats for subyearling chinook salmon 

 (Healey 1982, Reimers 1973, Myers 

 1980, Nicholas and Hankin 1988, 

 Levy and Northcote 1982). Residence 

 in estuaries of subyearling chinook 

 salmon can be as long as 3 months or 

 more (Reimers 1973, Myers 1980). 

 Growth rates of subyearling chinook 

 salmon are high in some estuaries 

 (Healey 1980, Levings et al. 1986, 

 Argue et al. 1986), but low in others, 

 perhaps because of competition for 

 food (Reimers 1973, Neilson et al. 

 1985). Because of the long period of 

 residence and active feeding of juve- 

 nile chinook salmon in estuaries, the 

 release of large numbers of hatchery 

 chinook salmon into a system could 

 impact survival and growth of wild 

 fish. The interactions among groups 

 of chinook salmon depend on their 

 overlap in the estuary in time and 

 space. 



Many large subyearling spring chi- 

 nook salmon smolts were released in 

 1987 into Coos Bay, C^regon, by Anad- 

 romous. Inc., a private salmon ranch- 

 ing facility. These fish ranged from 

 about 120 to 160 mm mean fork length 

 (FL) and were generally larger than 

 wild subyearling chinook salmon found 

 in Oregon estuaries (Reimers 1973, 

 Myers 1980, Nicholas and Hankin 

 1988). The large spring chinook salm- 

 on may compete with smaller fall chi- 

 nook salmon for estuarine resources. 

 However, estuarine dependency and 

 emigration rates of spring and fall 

 chinook salmon in Coos Bay are not 



known. To assess the potential for 

 competition between juvenile spring 

 chinook salmon released by Anad- 

 romous. Inc. and fall chinook salmon, 

 we studied their temporal and spatial 

 overlap in beach-seine samples. 



Methods 



We collected juvenile chinook salmon 

 in Coos Bay (lat. 43°21'N, long. 

 124°20'W) with a 60 x 2.5 m beach 

 seine between 25 April and 10 Octo- 

 ber 1987. The seine had 19- and 

 13-mm mesh (stretch-measure) in the 

 wings and bunt, respectively. The net 

 was set with the current using a 

 6.1-m dory powered by a 50 hp out- 

 board motor. Juvenile salmon were 

 counted, measured, and checked for 

 fin-clips immediately after capture. 

 When catches were large, juvenile 

 salmon were kept alive in a floating 

 net pen during processing. Salinity 

 was estimated with an American Op- 

 tical (Model TS) refractometer to the 

 nearest "Am and temperature mea- 

 sured to the nearest 0.1 °C. 



Five stations were sampled regu- 

 larly (Fig. 1). Stations 1, 2, 3, 4, and 

 5 were 2.0, 3.3, 6.5, 9.8, and 14.8 km, 

 respectively, from the mouth of the 

 bay. The Anadromous, Inc. release 

 facility was located on North Spit 

 between sites 3 and 4. On most dates 

 each station was sampled twice. 



Reference to trade names does not imply en- 

 dorsement by the National Marine Fisheries 

 Service, NOAA. 



51 



