25 



Abstract— Information is summarized 

 on juvenile salmonid distribution, size, 

 condition, growth, stock origin, and 

 species and environmental associations 

 from June and August 2000 GLOBEC 

 cruises with particular emphasis on 

 differences related to the regions north 

 and south of Cape Blanco off Southern 

 Oregon. Juvenile salmon were more 

 abundant during the August cruise as 

 compared to the June cruise and were 

 mainly distributed northward from 

 Cape Blanco. There were distinct differ- 

 ences in distribution patterns between 

 salmon species: chinook salmon were 

 found close inshore in cooler water all 

 along the coast and coho salmon were 

 rarely found south of Cape Blanco. Dis- 

 tance offshore and temperature were 

 the dominant explanatory variables 

 related to coho and chinook salmon 

 distribution. The nekton assemblages 

 differed significantly between cruises. 

 The June cruise was dominated by juve- 

 nile rockfishes, rex sole, and sablefish, 

 which were almost completely absent 

 in August. The forage fish community 

 during June comprised Pacific herring 

 and whitebait smelt north of Cape 

 Blanco and surf smelt south of Cape 

 Blanco. The fish community in August 

 was dominated by Pacific sardines and 

 highly migratory pelagic species. Esti- 

 mated growth rates of juvenile coho 

 salmon were higher in the GLOBEC 

 study area than in areas farther north. 

 An unusually high percentage of coho 

 salmon in the study area were preco- 

 cious males. Significant differences in 

 growth and condition of juvenile coho 

 salmon indicated different oceano- 

 graphic environments north and south 

 of Cape Blanco. The condition index 

 was higher in juvenile coho salmon to 

 the north but no significant differences 

 were found for yearling chinook salmon. 

 Genetic mixed stock analysis indicated 

 that during June, most of the chinook 

 salmon in our sample originated from 

 rivers along the central coast of Oregon. 

 In August, chinook salmon sampled 

 south of Cape Blanco were largely from 

 southern Oregon and northern Cali- 

 fornia; whereas most chinook salmon 

 north of Cape Blanco were from the 

 Central Valley in California. 



Manuscript approved for publication 

 30 June 2003 by Scientific Editor. 



Manuscript received 20 October 2003 

 at NMFS Scientific Publications Office. 



Fish. Bull 102:25-46 (2004). 



Juvenile salmonid distribution, growth, condition, 

 origin, and environmental and species associations 

 in the Northern California Current* 



Rick D. Brodeur 



Northwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 2030 S. Marine Science Drive 

 Newport, Oregon 97365 

 E-mail address: Rick-Brodeuriffinoaa-gov 



Joseph P. Fisher 



College of Ocean and Atmospheric Sciences 

 Oregon State University 

 Corvallis, Oregon 97331 



David J. Teel 



Northwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 Seattle, Washington 98112 



Robert L. Emmett 



Northwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 2030 S Marine Science Drive 

 Newport, Oregon 97365 



Edmundo Casillas 



Northwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 Seattle, Washington 98112 



Todd W. Miller 



Cooperative Institute for Marine Resources 



Studies 

 Oregon State University 

 Newport, Oregon 97365 



The need to understand the direct 

 and indirect linkages between oceano- 

 graphic conditions and salmon sur- 

 vival in the marine environment has 

 increased with the listing of many 

 West Coast salmon stocks as threat- 

 ened or endangered. Recent studies 

 have shown that long-term changes 

 in climate affect oceanic structure and 

 produce abrupt differences in salmon 

 marine survival and returns (Francis 

 and Hare, 1994: Mantua et al., 19971. A 

 major regime shift in the subarctic and 

 California Current ecosystems during 

 the late 1970s may have been a factor 

 in reducing ocean survival of salmon in 

 the Pacific Northwest and in increas- 

 ing marine survival in Alaska ( Hare et 

 al., 1999). Fluctuations in mortality of 

 salmon in the freshwater and marine 

 environments have been shown to be 

 almost equally significant sources of 

 annual salmonid recruitment variability 

 ( Bradford, 1995 ). Unlike in the freshwa- 

 ter environment, the physical and bio- 

 logical mechanisms and factors in the 

 marine environment that cause mor- 

 tality of salmon are largely unknown. 

 Predation, inter- and intraspecific 

 competition, food availability, smolt 

 quality and health, and physical ocean 

 conditions likely influence survival of 

 salmon in the marine environment. 



Thus, increasing our understanding of 

 nearshore ocean environments, their 

 linkages to oceanographic conditions, 

 and the role they play in salmonid 

 survival, could provide management 

 options for increasing adult returns. 

 Characterization of the space-time vari- 

 ability of the environmental conditions 

 that smolts encounter when they enter 

 the nearshore ocean, and the eventual 

 survival of these smolts will allow us to 

 identify which biotic and abiotic ocean 

 conditions are correlated with various 

 ocean survival levels. 



Many anadromous salmonid popula- 

 tions along the west coast of the United 

 States have declined over the last few 

 decades (Nehlsen et al., 1991), and most 

 stocks show a regional north-south pat- 

 tern in degree of extinction risk (Kope 

 and Wainwright, 1998). This pattern 

 suggests that both marine habitat con- 

 ditions and mesoscale climate patterns 

 affect salmonid population status (e.g. 

 Lawson, 1993). A dramatic example is 

 the population trend of coho salmon 

 (Oncorhynchus kisutch) along the Or- 

 egon coast. Populations along the coast 

 north of Cape Blanco (43°N) have exhib- 



; Contribution number 364 of the U.S. 

 GLOBEC program. NEP Office, Oregon 

 State University, Corvallis. OR. 



