FISHERY BULLETIN: VOL. 73, NO. 2 



t- i2 5 



^ 2 







J-F M-A M-J 

 BIMONTHLY 



J-A S-0 

 INTERVAL 



N-D 



Figure 2.-Mean marginal increments for six bimonthly inter- 

 vals from 78 specimens of Pimelometopon pulchrum from Cat- 

 alina Island. Sample sizes are shown for each interval, and 95% 

 confidence limits for the mean are drawn on either side of each 

 point. 



Table 1 shows the back-calculated lengths for 

 100 California sheephead from Catalina over eight 

 age groups, derived from spine radius 

 measurements. The means from back calculation 

 are also given in Figure 3 for comparison with 

 empirical data. The mean standard lengths for 

 each age (Figure 3) demonstrate good agreement 

 with the back-calculated data. 



There appears to be a slight slowing of growth 

 after the fourth year in the Catalina California 

 sheephead population. This may reflect the onset 

 of a diversion of a significant amount of energy 

 into egg production, since most 4-yr-old fish 

 examined were mature females (see below). A 

 second period of more rapid growth is suggested 

 after the seventh year, at an age where many of 

 the Catalina California sheephead are beginning 

 to transform from female to male. There is no 

 evidence for a decrease in the rate of growth up to 

 age 13, where the average standard length is 470 

 mm. Pimelometopon pulchrum is quite capable of 

 growing larger than this, and some individuals 



Table 1. -Back-calculated lengths for age groups 1 through 8 of Pimelometopon pulchrum 



from Catalina Island. 



tionality method given by Rounsefell and 

 Everhart (1953) as follows: 



L'-C 

 L-C 



^ 

 S 



where L = length of the fish at the time the spine 

 was obtained, L' = length at the time a particular 

 annulus was formed, S = total length of the spine 

 radius, and S' = length along the spine radius to 

 the annulus in question. The term C is a factor 

 used to correct for the length obtained before the 

 spine was formed, and is estimated by the inter- 

 cept of the length axis on a fish length versus spine 

 radius plot (Figure 1). In the case of the Catalina 

 California sheephead population, C was equal to 

 47.2 mm. 



have very long lifespans. Fitch and Lavenberg 

 (1971) mention a 32-inch (815-mm) male aged at 53 

 yr, and an 8.3-kg female, no length given, that was 

 30 yr old. Although exact age determination 

 becomes difficult for large and old individuals, it is 

 occasionally possible. The largest California 

 sheephead encountered in this study were a 592 

 mm SL male, 20 yr of age, and a 538 mm SL male 

 which had lived 18 yr. Size-age distributions can 

 vary for different locations. In a sample taken by 

 the California Department of Fish and Game at a 

 spearfishing meet at San Pedro, Calif., on 28 

 March 1971, the mean standard length for males 

 was 661 mm (range 545-745 mm) and for females 

 was 450 mm (range 294-656 mm). 



The pattern at Guadalupe Island is different 

 from that at Catalina (Figure 4). While the sample 



266 



