Kramer: Growth and mortality rates of juvenile Paralichthys californicus 



199 



Analysis of covariance also indicated no 

 significant difference between juveniles 

 from the bays and the open coast in the 

 relationship between length and age 

 (Table 2). The comparison was made be- 

 tween fish from the bays and the open 

 coast. The common slope was 0.471 (SE 

 0.0238). Therefore, I used the pooled data 

 for all estimates of growth (n 120). 



Length-at-age 



The relationship between standard length 

 (mm) and age (days) was best described 

 with the Gompertz growth function, 



Length = P ; x exp(P 2 (l - exp(-P 3 x age))) 



with Pj = 2.13, P 2 = 4.77, and P 3 = 0.011, and an esti- 

 mated mean square error of 0.99 (2SE Pl = 0.34, 

 2SE P , = 0.137, 2SEp 3 = 0.0013) (Fig. 5A). The param- 

 eter P^ closely estimates the length-at-hatching, which 

 is 2.0 for halibut (Ahlstrom et al. 1984). 



The relationship of age-at-length was determined 

 with the function, 



Age = 



-88.347 x In (In (standard length x 251.07)/ -4.769) 



derived from the Gompertz relationship for size-at-age 

 (Methot 1981) (Fig. 5B). The variance in the estimate 

 of age-at-length increases with increasing length; the 

 95% confidence interval (CI) for a halibut age 25 days is 

 ± 6 days, but for a 90-day-old halibut the 95% CI is 

 ± 19 days (Fig. 5). This relationship was used to con- 

 vert length-classes into age-classes using the mean of 

 each length-class (Lo 1985). 



I used the method outlined by Methot (1981, equa- 

 tions 1-5) to compute the age-specific daily growth 

 rates. Length-specific daily rate of growth and the 

 variability in growth rate increased with increasing 

 length: the slowest growth occurred just after transfor- 

 mation (SL 6-10 mm), with daily growth < 0.3 mm/day, 

 and maximum growth rates of about 1 mm/day oc- 

 curred in juveniles 70-120mm SL (between 110 and 

 160 days) (Fig. 6). These growth rates are similar to 

 those measured by Allen (1988) who estimated that 

 juveniles 21-29 mm SL grew at 0.36 mm/day, and juve- 

 niles 19-47 mm SL grew at 0.99 mm/day. 



Distribution and abundance 



Juvenile California halibut 16-70 mm SL were present 

 in the bays during January-July 1987 and March- 



< 



80 100 120 



AGE (days) 



40 60 80 100 



STANDARD LENGTH (mm) 



Figure 5 



Gompertz relationship with 95% confidence intervals fitted 

 to length-at-age of California halibut. (A) Standard length- 

 at-age; (B) estimated age-at-length (mm). 



September 1988, and on the open coast between May 

 and September 1988. The distribution of transforming 

 larvae and juveniles on the open coast differed for the 

 1987 and 1988 year-classes, with very few larvae and 

 no small juveniles taken on the open coast in 1987, 



