718 



Fishery Bulletin 102(4) 



in otolith cores with expected ingrowth curves through 

 time (Fig. 4). Of the 14 pooled otolith groups, three had 

 radiometric age ranges that fully encompassed the pre- 

 dicted age range, ten resulted in overlapping age ranges, 

 and one exceeded predicted age (Table 4). In addition, 

 radiometric ages were in close agreement with predicted 

 ages in a direct comparison (r 2 =0.88; Fig. 5). Further 

 Ntests indicated no significant difference in slope (£=1.92, 

 P=0.092) or elevation U=0.163, P=2.201) between the 

 regression and a hypothetical agreement line (slope of 

 1), confirming the close agreement of radiometric age 

 and predicted age. 



Discussion 



Estimation of age and growth 



The growth pattern present in otoliths of blackgill rock- 

 fish was often difficult to interpret. Complications inher- 

 ent to the growth pattern were the following: obscure 

 growth zones up to age 10-15 (the ages when the otolith 

 begins to thicken laterally), rapid transition to slower 

 growth, conflicting or ambiguous growth patterns, and 

 poor resolution of extremely compressed zones in old-age 

 fish. Irregular patterns may have led to enumeration of 

 false growth zones (checks), and the compression of the 

 outer layers may have concealed growth zones present in 

 older fish. This finding has been consistent among previ- 

 ous studies of rockfishes I Chilton and Beamish, 1982). 



1.2 

 1 1 

 1.0 

 0.9 

 0.8 

 0.7 

 06 

 0.5 

 04 

 0.3 

 0.2 

 0.1 

 0.0 



4^ 



^ 



=2 



i 



Expected Ingrowth Curve 



a Juvenile age groups 

 • Female age groups 

  Male age groups 



20 



40 60 



Sample age (yr) 



Figure 4 



Measured 210 Pb: 226 Ra ratio plotted against total sample age (mean 

 predicted age plus time since capture! of blackgill rockfish iSebastes 

 melanostomus), with respect to the expected 210 Pb: 226 Ra activity 

 ratio. Horizontal error bars represent the predicted age range (based 

 on age prediction model extended by 14.6% CV). Vertical error 

 bars represent high and low activity ratios based on the analytical 

 uncertainty associated with 2ln Pb and 226 Ra measurements. 



Because of the difficulty involved in interpreting growth 

 patterns, aging of blackgill rockfish otoliths involved a 

 high degree of individual subjectivity, as evidenced by 

 the relatively low precision (D=8.4%) and high varia- 

 tion (CV=15%) between readers. However, there were 

 some remarkably clear otoliths and for these we were 

 highly confident of age estimates (Fig. 1). Overall, 87% 

 of between-reader age estimates were within 10 years, 

 emphasizing that although the method of interpretation 

 of growth can be imprecise, it provides a reasonable 

 indication of the growth characteristics and longevity 

 of this species. 



The von Bertalanffy growth parameters for male 

 and female blackgill rockfish appear to indicate that 

 blackgill rockfish possess distinct patterns of growth 

 (Table 1). Female blackgill rockfish exhibited a slower 

 growth rate than males up to approximately 25-30 

 years of age (Fig. 2). At this point, the male growth 

 rate slows and approaches an asymptotic length of 448 

 mm, but females continue to grow in length, reaching 

 an asymptotic length of 548 mm. This trend of slower 

 growing, but ultimately larger females has been ob- 

 served in other slope-dwelling Sebastes species, such 

 as the darkblotched (S. crameri; Rogers et al., 20001, 

 and splitnose (S. diploproa; Wilson and Boehlert. 1990) 

 rockfishes. For both sexes, the growth coefficient is low 

 (k = 0. 040-0. 068) when compared to shallower-dwell- 

 ing (50-200 m) rockfishes, such as the greenstriped 

 (S. elongates, 0.10-0.12; Love et al., 1990) and widow 

 (S. entomelas, 0.20-0.25; Williams et al., 2000) rock- 

 fishes, but very similar to other deep-dwell- 

 ing, long-lived species, such as the short- 

 spine thornyhead (Sebastolobus alaseanus, 

 £ = 0.020; Cailliet et al., 2001), yelloweye (S. 

 ruberrimus, £ = 0.046; Andrews et al., 2002), 

 and bank (S. rufus, £ = 0.041; Cailliet et al., 

 2001) rockfishes. 



Previous maturity estimates for blackgill 

 rockfish (7-9 yr males, 6-10 yr females; 

 Echeverria 1987). based on whole otolith 

 counts, were much lower than estimates ob- 

 tained from section ages in the present study 

 (Table 2). Maturity estimates from our study 

 support those derived by Butler et al. (1999). 

 largely because the aging protocol was the 

 same between facilities. Although our growth 

 model included some age estimates (37%) 

 from Butler et al. (1999), our results further 

 confirm age at maturity (Table 2). Compared 

 to other species of the genus, blackgill rock- 

 fish have a late maturity that resides at the 

 upper end of the range for rockfishes (Cail- 

 liet et al., 2001; Love et al., 2002). 



Extraordinarily old ages in average-size 

 fish exhibited by the blackgill rockfish 

 should not be dismissed as an anomaly. In 

 this study the oldest blackgill rockfish was 

 a 90-year-old male (aged as high as 102 

 years) that was 450 mm TL. This fish was 

 160 mm less than the maximum reported 



100 



