RALSTON AND MIYAMOTO: OTOLITH INCREMENTS OF HAWAIIAN SNAPPER 



<P.c 



V = 4 9765 + 6286 X 

 N = 66 



I 1 1 1 1 1 1 1 1 1 1 1 I I I I I 



50 52 54 56 58 60 62 64 66 



Log, {Fork Length - mm) 



FIGURE 5.— Relationship between otolith length and fork length in 

 Pristipomoides filamentosus. 



There is pronounced curvilinearity in the data, as 

 well as heteroscedastic variance. The von Ber- 

 talanffy growth model (Ricker 1979) asserts that 

 somatic growth rate in length is a linear decreasing 

 function of length, with the X-intercept defining the 

 asymptotic upper bound on growth (L „). The obser- 

 vation that the growth-rate curve of opakapaka 

 otoliths is a concave (upwards), monotonic decreas- 

 ing function of otolith length (Fig. 6) is consistent 



30-| 





25- 



V 



OJ 

 LX 



20- 



15- 



o to. 

 O 



5- 



158 



2957 



3 / I 



I 256 88 32 4 



S § 



1 1 1 1 1 1 1 1 1 I 



2,000 4,000 6,000 8,000 10,000 



Otolith Length - u. 



FIGURE 6.— Relationship between otolith growth rate (increment 

 width) and otolith size in Pristipomoides filamentosus. Points repre- 

 sent means bracketed by standard deviations. Sample sizes are 

 given above each length class. 



with this notion, given the previously deduced 

 allometric relationship between fork length and 

 otolith length. 



Growth- rate data were logarithmically transformed 

 to linearize the trend line and stabilize the variance 

 (Fig. 7). It is evident that once the otolith reaches 

 about 6,000 fim in length, an alteration occurs in the 

 rate (slope) at which log-transformed growth rate 

 declines, maintaining a higher rate than would be ex- 

 pected otherwise. This noticeable change in slope is 

 apparently due to attainment of reproductive 

 maturity. 



Of those female opakapaka collected during the 

 summer spawning season (Kikkawa 1980; Ralston 

 1981), the incidence of gravid/soawning ovaries is 

 strongly dependent upon fish size (Fig. 8). These 

 data indicate that female opakapaka reach reproduc- 

 tive maturity at about 40 cm FL. Fish this length have 

 otoliths about 6,250 ju.m long (Fig. 5). Thus the dis- 

 tinct change in trend of otolith growth rate coincides 

 closely with maturation. Males shew a similar pattern 

 of gonad maturation (Ralston 1981). 



Based on these observations, it is likely that periods 

 of episodic growth commence in opakapaka otoliths 

 with the onset of maturity. That growth dynamics 

 should improve at this time, as suggested by a mod- 

 eration in the decline of log-transformed otolith 



3.0- 





o 



o 



c 



o 

 O 



oi 1.0 



o 



Mature 



"N 



1 1 1 1 1 1 1 1 1 1 



2,000 4,000 6,000 8,000 10,000 



Otolith Length - u. 



FIGURE 7.— Linearization of otolith growth rate data by logarithmic 

 transformation for Pristipomoides filamentosus. Points represent 

 means bracketed by standard deviations. 





529 



