26 



Fishery Bulletin 102(1) 



ited a strong decline in size and survival in the mid-1990s; 

 whereas populations south of Cape Blanco have not shown 

 this trend (Lewis 1 ). This finding suggests that these two 

 populations have experienced different ocean conditions. 



The quality of the marine habitat (in terms of habitat 

 complexity, prey density, and temperature) undoubt- 

 edly influences fish growth and condition. Growth and 

 indices of condition can be used as measures of habitat 

 quality for juvenile salmon and to identify essential links 

 between oceanographic conditions and survival of salmon 

 populations during the critical juvenile life history phase. 

 Measures such as growth (growth rate, size variation, and 

 allometric relationships) (Lorenzen, 1996; McGurk, 1996) 

 and accumulation of energetic reserves used in growth and 

 sustenance during the low-productivity winter periods 

 have been used previously to characterize habitat quality 

 and to describe how it ultimately affects the individual and 

 the population (Perry etal., 1996; Paul and Willette, 1997). 

 Environmental factors are known to affect growth, repro- 

 duction, survival, and ultimately population recruitment 

 (Hinch et al., 1995; Marschall and Crowder, 1995; Fried- 

 land and Haas, 1996). As such, fish condition, growth rate, 

 and size in the pre-adult stages are parameters that can be 

 used to identify the influence of natural and anthropogenic 

 ocean conditions on marine survival. 



Much of our current knowledge of the dominant nekton 

 of the pelagic ecosystem off the coasts of Oregon and Wash- 

 ington is derived from a series of 17 cruises conducted by 

 Oregon State University (OSU) from 1979 to 1985. These 

 collections, consisting of >900 quantitative purse seine sets 

 in the northern California Current, were made to examine 

 geographic distributions and temporal trends of the domi- 

 nant nekton and how these relate to physical and biotic 

 conditions at the time of capture. The primary purpose 

 of these cruises was to collect data for assessment of the 

 abundance, distribution, growth, migration, and ecology of 

 juvenile salmon in coastal waters. Data on the distribution, 

 migration and growth of juvenile salmon from these cruises 

 have been summarized in Fisher and Pearcy (1988; 1995). 

 Pearcy and Fisher ( 1988, 1990), and Pearcy ( 1992). Analy- 

 sis of the nonsalmonid data includes studies on their abun- 

 dance and distribution (Brodeur and Pearcy, 1986; Emmett 

 and Brodeur, 2000), feeding habits (Brodeur et al., 1987) 

 and interannual variability in relation to oceanographic 

 conditions (Brodeur and Pearcy, 1992). In addition, the 

 distribution of juvenile salmon (mainly coho and chinook 

 salmon [O. tshawytscha}) has been studied more recently 

 as a component of a multiyear Columbia River Plume study 

 (Emmett and Brodeur, 2000; Teel et al., 2003; Brodeur et 

 al., 2003). However, all these cruises extended only as far 

 south as Cape Blanco, with the exception of one cruise (July 

 1984), which extended as far south as Eureka, California, 

 but included only a few collections south of Cape Blanco 

 (Pearcy and Fisher, 1990). Thus, the region south of Cape 

 Blanco is almost completely unknown in terms of juvenile 



1 Lewis, M. A. 2002. Stock assessment of anadromous salmo- 

 nids 2001. Monitoring program report OPSW-ODFW-2002-04, 

 57 p. Oregon Dept. Fish Wildlife, Portland. OR 97207. 



salmon distribution, pelagic nekton, and biological ocean- 

 ography in general, despite being an area of very strong 

 upwelling and high productivity. Also, the fine-scale dis- 

 tribution of juvenile salmon in relation to environmental 

 variables has not been studied in any detail. 



The California Current is not homogeneous but rather 

 can be divided into distinct subunits or regions, each with 

 its own physical and biological characteristics (U.S. GLO- 

 BEC, 1994). A break between the northernmost two regions 

 occurs at Cape Blanco, where the equatorward upwelling 

 jet veers sharply off the shelf and into the California Cur- 

 rent (Barth et al., 2000). The upwelling zone north of the 

 cape is narrow, extending out about 30 km, whereas south 

 of Cape Blanco, it can extend up to 100 km offshore. This 

 area also appears to represent a faunal break for some zoo- 

 plankton communities (McGowan et al., 1999; Peterson and 

 Keister, 2002) and is a break point for alternative salmon 

 migration strategies (Weitkamp et al., 1995; Weitkamp and 

 Neely, 2002). 



During the summer of 2000, we conducted broad-scale 

 sampling and fine-scale process studies from central Or- 

 egon to northern California to examine the distribution 

 of juvenile salmon and associated species in relation to 

 environmental conditions. This was one component of a 

 multidisciplinary U.S. Global Ocean Ecosystem Dynamics 

 (GLOBEC) Northeast Pacific study examining the north- 

 ern California Current ranging in scope from the physics 

 up to the top trophic levels (Batchelder et al., 2002). We 

 were interested in examining the distribution of juvenile 

 salmon north and south of Cape Blanco, the origin of these 

 fish, and any regional differences in growth and condition 

 of salmon across the range of sampling. Evidence exists 

 that the physical conditions and the associated biota are 

 different within this geographical scale. Thus, analyses of 

 the relationship between oceanographic conditions and the 

 response of resident biota can provide insights into the 

 linkages associated with physical and biological processes 

 that shape the biological community, and in particular, 

 those associated with salmon recruitment. 



Methods 



Field surveys 



Surveys were conducted over two time periods — early 

 summer (29 May-18 June, 2000) and late summer (28 

 July-15 August, 2000). Each survey consisted of a meso- 

 scale grid along designated GLOBEC transects that had 

 been monitored for several years and by fine-scale pro- 

 cess sampling at stations of interest based on features 

 observed in the physical environment (fronts or eddies) 

 or by acoustic sampling conducted by two accompanying 

 oceanographic vessels (RV Wecoma and RV New Horizon). 

 Further details on the physical and biological conditions 

 occurring at the time of our sampling have been reported 

 by Batchelder et al. (2002). 



For the mesoscale survey, stations were established at 

 1, 5, 10, 15, 20, 25 and 30 nautical miles from shore on 

 each of five transects. Inclement weather, particularly 



