44 



Fishery Bulletin 102(1) 



data (Teel et al., 2003). Samples from subsequent cruises 

 will be used to examine the persistence of such fine- and 

 broad-scale geographic structure in the juvenile migrations 

 of salmonid stocks. 



A major source of error in our estimates of growth rates 

 of juvenile coho salmon back-calculated from scales was 

 uncertainty of when individual fish entered the ocean. We 

 used a single date of ocean entry for all fish (15 May), but 

 individual fish, of course, entered the ocean at different 

 times over the course of a month or more. Consequently, 

 coefficients of variation were relatively large (84—119% and 

 75-120% of mean growth rate in FL and weight, respec- 

 tively) for fish caught in May and June, when errors in es- 

 timated growth periods likely were large in relation to the 

 actual growth periods. Conversely, coefficients of variation 

 were relatively small ( 14-30% and 10-26% of growth rate 

 in FL and weight, respectively) for fish caught in August or 

 September, when errors in estimated growth periods likely 

 were small in relation to the actual growth periods. (Note 

 the decrease in standard deviation of mean growth rates 

 with month of capture in Tables 3 and 4A). Growth rates 

 of CWT coho salmon between hatchery release and capture 

 in the ocean (Table 4B) were very similar to the growth 

 rates of unmarked salmon estimated from scales for the 

 same months and areas. In addition, the growth rates of 

 the former group ( CWT coho salmon ) helped to validate the 

 growth rates of the latter group (Table 4A). 



Significant differences in growth and condition of ju- 

 venile coho salmon indicate that different oceanographic 

 environments exist north and south of Cape Blanco. The 

 length of the fish indicated that substantial growth oc- 

 curred in juvenile coho salmon during the study period. As- 

 sessment of other growth features (condition) revealed that 

 juvenile coho salmon grew better north of Cape Blanco. 

 Because we included measurement of condition in both the 

 June and August period in the evaluation, changes in stock 

 composition, described earlier, may be partly responsible 

 for this observation. Although genetic stock composition 

 was different between months, month of sampling was not 

 a significant factor, suggesting that stock composition is 

 not likely a significant factor affecting the difference in 

 condition (a performance metric) of juvenile salmon north 

 and south of Cape Blanco. 



Several lines of evidence further support the hypothesis 

 that areas north of Cape Blanco benefit juvenile yearling 

 chinook and coho salmon. There were greater numbers of 

 juvenile yearling chinook and coho salmon to the north of 

 Cape Blanco. Although our overall sampling effort was 

 greater north of Cape Blanco, in the mesoscale portion of 

 our survey designed to assess general distribution patterns, 

 more yearling chinook and coho salmon were captured 

 north of Cape Blanco. Secondly, when we evaluated the 

 growth rate of juvenile coho salmon in the GLOBEC region 

 compared to juveniles captured off northern Oregon and 

 Washington, juveniles from the GLOBEC region grew much 

 better. The similar tracking of resource (distribution and 

 abundance) and performance (measured in terms of either 

 somatic and energetic growth or growth rate) metrics for 

 juvenile yearling chinook salmon and coho salmon ninth 

 of Cape Blanco suggests that habitat quality in this region 



was better. The results of this study help define the biogeo- 

 graphical zones for salmon growth and establish regional- 

 based management strategies for depleted salmon stocks. 



Acknowledgments 



We thank the captain and crew of the FV Sea Eagle for their 

 expert help in conducting the trawling operations under 

 sometimes adverse weather conditions. We are grateful 

 to Jackie Popp-Noskov, Paul Bentley, Marcia House, and 

 Becky Baldwin for assistance in field sampling. Donald 

 Van Doornik and David Kuligowski collected the genetic 

 data. We thank Anne Marshall for the use of unpublished 

 chinook salmon allele frequency data. Stephen Smith 

 and Alex De Robertis helped with the statistical analy- 

 sis. Earlier versions of this manuscript were improved 

 by the helpful comments of two anonymous journal 

 reviewers. Research was conducted as part of the 

 U.S. GLOBEC program and was jointly funded by the 

 National Science Foundation (Grant no. OCE-0002855) 

 and the National Oceanic and Atmospheric Administra- 

 tion (NOAA). We also acknowledge the Bonneville Power 

 Administration for funding the plume study. 



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