Laidig et al.: Age and growth of Sebastes mystinus 



805 



curves were not statistically different (Table 1). Therefore, 

 these regimes did not appear to effect the growth of adult 

 fish. Out of the four other surveys mentioned above, three 

 came from one of these two regimes, and the fourth, Miller 

 and Geibel (1973), came from an earlier regime. If there 

 were any effects from the three different thermal regimes, 

 it would seem clear that these differences would show up 

 between samples from such varied regimes. However, the 

 only study with different measures of growth was that from 

 Oregon (McClure, 1982), with samples that were collected 

 during the same regime as two of the other studies (Mac- 

 Gregor, 1983; and the present study). Therefore, thermal 

 regime alone does not seem to have a major impact on the 

 growth of blue rockfish, although further analysis is needed 

 to confirm this point. 



These differences in growth parameters between fish 

 from California and Oregon may be attributed to differ- 

 ences in aging methods. Wilson and Boehlert (1990) found 

 that estimates of growth based on aging of otolith surfaces 

 were higher for Sebastes pinniger, but were similar to 

 growth rates estimated from otolith sections for S. diplo- 

 proa. The ages of S. alutus determined from otolith surfaces 

 had poor correlation with ages from otolith cross-sections 

 for fish older than 17 years, but there was close agreement 

 for younger fish (Stanley and Melteff 1987). Reading ages 

 from the surface of an otolith may underestimate the age 

 of a rockfish (Munk, 2001) and thus result in greater size- 

 at-age and growth rate estimates. However, aging methods 

 may not be the only factor influencing the growth discrep- 

 ancies. Miller and Geibel (1973) and MacGregor (1983) 

 both used scales to age blue rockfish (which also can under- 

 estimate the age offish [Beamish and MacFarlane, 1987]), 

 and, yet, their growth models more closely approximated 

 the model produced by our study. 



Faster growth estimated for blue rockfish off Oregon 

 may reflect a latitudinal difference in growth. Fraidenburg 

 (1980) examined length and age composition of Sebastes 

 flavidus and reported evidence of a north-to-south cline 

 of decreasing size-at-age. Pearson and Hightower (1991) 

 studied S. entomelas and noted smaller k values and larger 

 average maximum lengths with increasing latitude. Boe- 

 hlert and Kappenman ( 1980) reported faster growth in the 

 north for S. diploproa and no difference in growth with 

 latitude for S. pinniger. They postulated that because the 

 fish live demersally on the continental shelf latitudinal 

 variation in environmental factors may be insufficient to 

 explain the difference in growth rates and that differential 

 exploitation by the fishery may be a possible influence on 

 growth. Blue rockfish live at relatively shallow depths 

 where environmental and biological factors may have a 

 greater influence on their populations. 



Although blue rockfish display a possible latitudinal 

 trend in growth rate between California and Oregon, 

 within California no latitudinal trend in growth rates was 

 observed. Specimens from both the southern CPFV sample 

 and the northern speared sample areas had translucent 

 zone completion by 1 May, which was consistent with the 

 findings of Miller and Geibel (1973) using ages from scales. 

 Individual fish in our study also had similar maximum ag- 

 es and maximum fish lengths in the north and south areas. 



10 



20 



30 



40 



50 



1° '*^° Females 



400 

 350 

 300 

 250 

 200 

 150 

 100 

 50 



10 



20 30 



Age (yr) 



40 



50 



Figure 6 



Von Bertalanffy growth models for male and female 

 blue rockfi.sh ^Sebastes mystinus) from the CPFV 

 (thick Hne) and speared samples (narrow line). 

 Individual data points are plotted for blue rockfish 

 from CPFV (open circle) and speared samples (open 

 triangles). 



No latitudinal trend in growth rates was observed over 

 the 280 km between the centers of the two sampling ar- 

 eas. Although growth rates varied throughout their study 

 area from Half Moon Bay in the north to Morro Bay in 

 the south. Miller and Geibel (1973) likewise observed no 

 latitudinal trend in growth for blue rockfish. 



Blue rockfish have average maximum ages and growth 

 rates when compared to other rockfish species. Maximum 

 ages for rockfishes {Sebastes spp.) range from 12 years for 

 the relatively small calico rockfish to 205 years for rough- 

 eye rockfish, one of the largest species (Cailliet et al., 2002; 

 Love et al., 2002). According to Love and Johnson (1998), 

 of the 38 species most accurately aged, most lived to more 

 than 40 years. Love et al. (1990) found growth rates for 

 three species that share the blue rockfish habitat (black, 

 /fe=0.12-0.21/year;yellowtail,^=0.16-0.20/year; and widow 

 rockfish, /j=G.14-0.22/year) to be similar to that for blue 

 rockfish (k=0.n years). Mean k values for rockfish varied 



