FISHERY BULLETIN: VOL. 87. NO. 1 



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A S O N D 



Month 



Figure 9.— The seasonal pattern of variation in mean gonadosomatic indexes of male and female 

 gindai in the Mariana Archipelago. Note that mean index values are bracketed by sample standard 

 deviations with the sample sizes given above. 



reached a peak in May and diminished as the sum- 

 mer progressed. 



The same pattern was mirrored in the percent- 

 age of ovaries classified to stages IV- VI (i.e., ad- 

 vanced developing to ripe). During the January- 

 March quarter, only 1.4% of the ovaries sampled 

 were so classified. This statistic rose to 48.3% dur- 

 ing the April-June period, but then dropped to 

 19.2% in the July- September quarter and to 16.7% 

 over the last quarter of the year (October-Decem- 

 ber). The similarity of these two patterns reinforces 

 the interpretation of reproductive seasonality based 

 on gonadosomatic indexes alone (but see deVlam- 

 ing et al. 1982), and when taken together, these data 

 indicate that peak spawning of gindai in the Mari- 

 ana Archipelago occurs in late May and early June. 



DISCUSSION 



Other researchers also have measured the width 

 of daily increments to study fish growth. Methot 

 (1981) used the widths of the outermost three incre- 



ments in the otoliths of Engraulis mordax and 

 Stenobrachius leucopsarus as a measure of recent 

 somatic growth rate. Brothers and McFarland 

 (1981) measured the thickness of daily increments 

 in newly recruited Haemulon flavolineatum to dis- 

 criminate life history transitions, as did Gutierrez 

 and Morales-Nin (1986) in their study of Dicentrar- 

 chus labrax. Moreover, integration of increment 

 width data to estimate age has been reported, both 

 analytically for Pristipomoides filaTnentosus (Ral- 

 ston and Miyamoto 1981, 1983) and numerically for 

 Merluccius angustimanus, Merluccius sp., Engrau- 

 lis mordax, and Pristipomoides auricilla (Brothers 

 et al. 1976; Methot 1983; Ralston 1985). 



Experimental work has revealed some of the fac- 

 tors that affect the width of daily growth incre- 

 ments. For example, decreased somatic growth in 

 Oncorhynchus tshawytscha due to reduced temper- 

 ature also results in reduced increment thickness 

 (Neilson and Geen 1985). There is conflicting evi- 

 dence, however, regarding the effect of food ration 

 on daily increment width. Volk et al. (1984) experi- 



10 



