Woodbury and Ralston; Growth rates and birthdate distributions of Sebsstes spp off central California 



529 



Yellowtall rockfish Juvenile yellowtail rockfish com- 

 prised the fewest specimens collected of the five species 

 studied. Sufficient specimens for growth analysis were 

 collected only in the years 1985-88. The scattergram 

 (Fig. 7) shows the smallest range in standard length 

 and age observed. This problem is exemplified in 1985 

 when the ages ranged only 107-133 days. 



The data were fitted by linear regression for each 

 year (Table 2) resulting in estimates of growth rate that 

 ranged from 0.194 mm/day in 1985 to 0.463 mm/day in 

 1 986. The descending sequence of estimated annual 

 growth rates of yellowtail rockfish was: 1 986 > 1987 

 >1988>1985. Results of ANCOVA (Table 3) testing 

 for annual differences in slope were borderline (P 

 0.104); all possible pairwise LSD comparisons (Fig. 3) 

 showed that growth rate in 1985 was slower than in 

 other years. An F-test of annual differences in adjusted 

 means was significant (Table 3, P 0.001). Like widow 

 rockfish, results from all possible pairwise comparisons 

 of yearly adjusted mean standard length indicated that 

 yellowtail rockfish juveniles were larger in 1987 than 

 in other years, with fish sampled in 1986 and 1988 

 somewhat larger (P 0.05-0.10) than those taken in 

 1985. The rank order of adjusted mean standard length 

 was identical to that observed in widow rockfish (i.e., 

 1987M986M988M985). 



Annual growth performance 



The data presented thus far make it difficult to com- 

 pare and contrast the growth of the five species on 

 an annual basis. For example, results from bocaccio 

 (lower panel in Figure 4) show that 1985 was char- 

 acterized by the highest growth rate (0.974 mm/day). 

 Even so, 90-day-old fish in 1985 were estimated to be 

 smaller than in any other year. In this situation it is 

 possible that poor growth performance during early- 

 life-history stages, prior to those sampled, had no 

 lasting effect on growth at the time of sampling. There 

 may even have been some form of compensatory 

 growth response. 



To overcome this problem we compared annual 

 growth performance within and among species by 

 estimating length at a selected standard age with the 

 regression statistics presented in Table 2. This is func- 

 tionally equivalent to integrating annual growth rates 

 up to the selected standard age, providing a common 

 basis for comparison among years. The standard age 

 for each species was determined from the range of ages 

 sampled in the various years. Standard ages were 

 selected to prevent extrapolation of the regressions. 

 Specific ages selected were: shortbelly rockfish 70 days, 

 bocaccio 100 days, chilipepper 90 days, widow rockfish 

 100 days, and yellowtail rockfish 107 days. 



100 



80 



60 





20 



20 40 60 80 100 120 14-0 160 180 

 Age (d) 



Figure 7 



Scattergrams of yellowtail rockfish Sebastesjlavidus standard 

 length on age for each year, 1985-88 (upper), with fitted linear 

 regressions to each year of data (lower). 



60 



50 



30 



20 



• bocaccio (100 t 

 a widow (100 d) 

 a yellowtail (107 t 



-o shortbelly (70 d) 

 -A chilipepper (90 d) 



82 



84 



85 86 



Year 



87 



89 



Figure 8 



Annual estimates (1983-88) of standard length at standardized 

 ages of shortbelly, bocaccio, chilipepper, widow, and yellowtail 

 rockfishes. 



Results show coherent differences in growth perfor- 

 mance from year to year (Fig. 8). Among the five 

 species over the last four years of the study, 1985 con- 

 sistently produced the smallest fish and, with the ex- 

 ception of shortbelly rockfish, 1987 yielded the largest 

 fish observed. Although only represented by two 



