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FISHERY BULLETIN: VOL. 87, NO. 4, 1989 



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1950 



1960 



Year 



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1970 



h 



1980 



Figure 8. — Comparison of the smoothed first principal component 

 time series of Sebastes piiiniger (dashed Hne) and S. diploproa (solid 

 hne) with data on the stock size of S. aiutus (circles) from Oregon, 

 Washington, and British Columbia (Ito et al. 1987). 



typically have a limiting juvenile habitat (often 

 estuarine) and a much more extensive adult 

 habitat. Indeed, Peterman and Bradford (1987) 

 have suggested that density-dependent gi'owth 

 of English sole, Parophrys vetulus, off the coast 

 of Oregon occurs only in the first year of life but 

 not later. In S. diploproa, the opposite occurs. 

 The adult habitat is restricted bathymetrically 

 and latitudinally, whereas the pelagic prejuven- 

 iles occur in a very extensive epipelagic habitat 

 subject to different environmental factors, com- 

 petitors, and food resources. It is doubtful that 

 variations in density of Sebastes in this habitat 

 would impact growth significantly. In the adult 

 habitat of both S. pinniger and S. diploproa, 

 however, the immense virgin biomass of mem- 

 bers of this genus has been reduced significantly. 

 Further, most rockfish species commercially ex- 

 ploited by the trawl fishery rely on the same food 

 resource, with euphausids as the principal prey 

 (Phillips 1964; Brodeur and Pearcy 1984). The 

 increased availability of prey resources asso- 

 ciated with stock decline could conceivably result 

 in increased growth in most species. Snytko and 

 Fedorov (1974) suggested that some rockfish 

 species have increased their geogi'aphic ranges 

 at the expense of the decreased stocks of S. 

 aiutus; density-dependent growth could be a 

 corollary of such a range extension. 



The nonstationary characteristic due to the 

 sudden increases in growth late in the time 

 series makes correlations of gi-owth indexes with 

 environmental factors difficult to evaluate. 

 Further, sea level, wind stress curl, and the first 

 principal component time series of S. diploproa 



and S. pinniger were all serially correlated in the 

 1946-77 data base, indicating temporal trends 

 that decrease the number of independent de- 

 gi'ees of freedom in the sample correlation esti- 

 mates and that introduce potentially spurious 

 correlations (Chelton 1983, 1984; Bakun 1985). 

 Correlations of the relationship of gi'owth data to 

 time series of physical factors (sea level, sea- 

 surface temperature, upwelling index, and wind 

 stress curl) were determined (Table 1); the 95% 

 significance levels were calculated using the 

 formula in Chelton (1983), which accounts for the 

 reduced number of degrees of freedom from 

 serial correlations. For S. pinniger, a signifi- 

 cant, positive correlation existed between the 

 second principal component and both the April- 

 September upwelling index and sea level (Table 

 1); a significant, positive correlation also existed 

 between both growth for age group 6 (G6 in 

 Table 1) and the second principal component 

 with the April-September upwelhng index for 

 the prior year. Growth in age group 6 con- 

 tributed significantly to the variance described 

 by the second principal component (Fig. 5A), so 

 the similarity was not surprising. Feeding by S. 

 pinniger increased during the spring-summer 

 upwelling period when Euphansia pacifica was 

 the dominant diet item and the frequency of 

 empty stomachs was lower (Brodeur and Pearcy 

 1984). This must also be the time that fat deposi- 

 tion occurs in this species since the peak fat con- 

 tent was in fall (Guillemot et al. 1985). The 

 effects of upwelling in a prior year on growth 

 may be related to delayed growth using the 

 energy from stored fat reserves built up during 



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