Brodeur et al.: Distribution, growth, condition, origin, and associations of |uvenile salmonids 



41 



Table 8 



Results of statistical tests for habitat associations between juvenile salmon and environmental or station variables from each 

 cruise in 2000. Fish marked by zeros indicate subyearlings and those marked with one indicate yearlings. Shown are the P-levels 

 for 5000 randomizations of the cumulative frequency of the habitat variable and the proportion of the standardized salmon catch 

 associated with each habitat observation. Results are based on the Cramer von-Mises test statistic determined from binned data 

 for depth and neuston biomass. Significance values <0.05 are shown in boldface. 



Cruise 



Jun 



Aug 



There were few instances where the habitat associations 

 of juvenile salmon were significantly different from the 

 distribution of environmental variables sampled (Table 8). 

 None of the variables were significant for yearling chinook 

 and coho salmon in the June sampling (no subyearling 

 salmon were caught during that cruise). In August, all 

 the variables except neuston biomass were significant for 

 yearling chinook salmon. These fish were collected at cooler 

 temperatures, higher salinities, higher chlorophyll-o con- 

 centrations, and at shallower depths than have been typi- 

 cally recorded (Fig. 9). Coho salmonjuveniles were found in 

 higher salinities and shallower depths than at the sampled 

 habitat (Fig. 9). These results correlated with the capture 

 of juvenile chinook salmon and to a lesser with extent coho 

 salmon at nearshore stations in the upwelling zone. 



Discussion 



Understanding the mechanisms underlying the dynamics 

 of multispecies communities is one of the biggest challenges 

 in ecology. Most communities contain many interacting spe- 

 cies, each of which is likely to be affected by multiple biotic 

 and abiotic factors. In order to effectively characterize a 



system, we need to differentiate variability resulting from 

 both temporal and spatial factors. Our observations took 

 place during two time periods of about 20 days each and 

 thus were not synoptic "snapshots" of the system. Indeed, 

 during our June sampling, conditions changed markedly 

 from the beginning to the end of the cruise because of the 

 arrival of an anomalous major southwest storm ( Batch- 

 elder et al., 2002), which likely completely altered the 

 hydrography and biology of the system. Thus, short-term 

 temporal variability may obscure patterns observed over 

 the spatial scale of our sampling. 



The pelagic nekton community sampled during these 

 cruises was not that different from what had previously 

 been shown for purse seine and trawling collections off 

 the coast of Oregon and Washington ( Brodeur and Pearcy, 

 1986; Emmett and Brodeur, 2000; Brodeur et al., 2003). 

 The early summer nekton community was dominated by 

 coastal forage fishes such as smelts and Pacific herring, 

 but also comprised juveniles of many rockfish, sculpin, 

 and flatfish species. These winter-spring spawning species 

 eventually settle out to demersal habitats sometime in 

 summer (Shenker, 1988; Doyle, 1992), which may in part 

 explain the paucity of these taxa in the August cruise. In 

 contrast, the August nekton community consisted of large, 



