FISHERY BULLETIN: VOL. 87, NO. 1 



that annuli have been validated (Fig. 6), verifies the 

 method of increment widths employed here. Like- 

 wise, the Monte Carlo simulation demonstrated that 

 from an analytical point of view the method is free 

 of significant bias. 



The results obtained here were also compared to 

 what we know of lutjanid growth by using the 

 growth performance index developed by Munro and 

 Pauly (1983) (see also Pauly and Munro 1983). For 

 a specifically delimited taxon, this index empirical- 

 ly quantifies the well-known inverse correlation be- 

 tween K and L„ (Beverton and Holt 1959; Gushing 

 1968) and provides a simple basis for predicting K 

 with an estimate of L„. Specifically, Manooch 

 (1987) tabulated the results of growth studies cover- 

 ing 46 snapper and 31 grouper (Epinephelinae) 

 stocks and calculated the combined growth perfor- 

 mance regression for these taxa (r^ = 0.57). With 

 his equation, we predicted K by using each of our 

 three estimates of L„ (see above). These calcula- 

 tions resulted \n K = 0.228, 0.200, and 0.220 yr"' 

 for maximum sizes derived from daily increment 

 microstructure, annuli, and length-frequency anal- 

 ysis, respectively. The estimates compare favorably 

 with the value obtained solely from the study of 

 otolith microstructure (K = 0.234 yr^'). indicating 

 that our results are in close agreement with exist- 

 ing information concerning lutjanid growth. 



Calculating the age at first annulus formation pro- 

 vides additional evidence that the approach pre- 

 sented here is valid. The data presented in Table 3 

 indicate that the first annulus occurs at an otolith 

 length of 3,1 17 yxn. An estimate of age at this oto- 

 lith length can be obtained from Table 2 by linear 

 interpolation of the data falling in otolith length in- 

 tervals 6 and 7; i.e., the otolith is 3,000 \ixa at age 

 0.6 and is 3,500 \im at age 0.8. This calculation in- 

 dicates that the first annulus forms at an age of 0.65 

 year. Given that the opaque zone forms in January- 

 February (Fig. 6), the predicted birth date by back- 

 calculation is early June, in close agreement with 

 observed spawning activity (Fig. 9). Moreover, the 

 mean monthly sea surface temperature at Tanguis- 

 son Point, Guam, reaches its annual minimum dur- 

 ing January-March (data for the period 1963-72 

 from Eldredge (1983)), suggesting that temperature 

 fluctuation may be responsible for the formation of 

 the annuli, although this species is found below the 

 thermocline throughout the year (Eldredge 1983) 

 and other closely related sympatric species lack 

 zonations. 



Some consideration of the underlying assump- 

 tions, advantages, and disadvantages of the method 

 presented here is required. Without doubt, the most 



important assumption of the approach is that incre- 

 ments are deposited daily throughout the size range 

 where increment width data are gathered. There is 

 a substantial body of literature to show that inter- 

 ruptions to the daily increment record can occur 

 (e.g., Geffen 1982, 1986; McGurk 1984; Jones 1986), 

 especially in larger and older individuals (e.g., Pan- 

 nella 1971; Ralston and Miyamoto 1983). Likewise, 

 we know that with light microscopy the resolution 

 of increments much less than 1.0 \m\ in width is 

 physically impossible (Campana and Neilson 1985). 

 This problem therefore becomes increasingly acute 

 among the largest fish (see Table 2 and Figure 3). 

 Together these findings have led to the view that 

 daily growth increments are of little use in ageing 

 large, old fish (Beamish and McFarlane 1987). 



In this study, the deposition of daily increments 

 became irregular at otolith lengths in excess of 7,500 

 /jm. Beyond this length, the increments were also 

 difficult to resolve microscopically due to small size. 

 Consequently, no increment width data were col- 

 lected at otohth lengths >7,500 \im. This corre- 

 sponds to a FL of 329 mm (Fig. 1), which, although 

 of a size that is reproductively competent (S. 

 Ralston, unpubl. data), is smaller than most of the 

 gindai caught during the field surveys (Fig. 7). Thus, 

 the estimated von Bertalanffy curve presented here 

 is largely based on back-calculated data obtained 

 from the younger stages of growth. Nonetheless, 

 we believe that daily increments can be useful in 

 developing growth curves for use in stock assess- 

 ments, even if data representing the older stages 

 are not included in the analysis. This is especially 

 true if the L„ parameter is estimated from length- 

 frequency data (Fig. 8, Wetherall et al. 1987), 

 avoiding the extrapolation problem described by 

 Hirschhorn (1974). Still, validation of the increment 

 periodicity assumption remains an essential compo- 

 nent for future applications of the method. 



Another assumption implicitly made is that no 

 systematic bias was introduced into the estimation 

 procedure by the manner in which sampling loca- 

 tions were chosen for measuring increment widths. 

 For example, readings were made at specific points 

 along the postrostral growth axis, i.e., where it was 

 possible to distinguish the characteristic bipartite 

 structure of daily increments. However, we also 

 observed broad transition areas lacking in visually 

 conspicuous microstructural features. If these ill- 

 defined regions were elicited by periods of either 

 fast or slow growth, then our estimates of mean 

 otolith growth rate would be biased. To counter this 

 we tried to representatively sample all daily incre- 

 ments (large and small) and we avoided measure- 



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