366 



Fishery Bulletin 88(2). 1990 



Figure 4 



Seasonal maturation cycle of male Scomberomorus cavalla (>54.5 

 cm) by (a) mean monthly GSI and (b) monthly percentages of ripe 

 (ripe and ripe-running) gonads. N = number of fish sampled. 



Figure 5 



Seasonal maturation cycle of female Scmnheromortis cavalla (>58.5 

 cm) by (a) mean monthly GSI and (b) nicmthly percentages of ripe 

 gonads. N = number of fish sampled. 



data when the annulus is apparently formed as fish 

 were scarce from November to February. Maximum 

 (bimonthly) percentages of opaque otolith margins 

 compare well with those (monthly) of North American 

 studies (Beaumariage 1973, Johnson et al. 1983, 

 Manooch et al. 1987). However, in the present study 

 the minimum (bimonthly) percentage (20%) was much 

 higher than in North America where in all the studies 

 there were one or more months wath no edged otoliths. 

 In Trinidad the period September to March, when 

 maximum percentages of opaque otolith margins are 

 found, corresponds with the period of greatest spawn- 

 ing intensity. In Brazil, the opaque ring is laid down 

 from November to March corresponding to a period of 

 intense spawning (Ximenes et al. 1978). Otoliths of 

 North American fish generally had the largest percent- 

 ages of opaque margins from April through Jiuie (Beau- 

 mariage 1973, Johnson et al. 1983, Manooch et al. 1987) 

 at the start of a well-defined spawning season (Beau- 

 mariage 1973, Finucane et al. 1986). The process of 

 spawning may therefore be related to annulus forma- 



tion in S. cavalla. If first spawning takes place at age 

 II, as might occur on occasion for Trinidad S. cavalla, 

 an annulus in immature (age-I) fish may be explained 

 by some internal physiological rhythm, together with 

 the environmental changes that trigger spawning, 

 causing annulus formation. This explanation was put 

 forward for annulus formation in immature fish for 

 hake Merluccius meriuccius (Hickling 1935) and red 

 snapper Lutjanus campechanus (Nelson and Manooch 

 1982). As spawning is year-round in the tropical waters 

 around Trinidad, the finding of relatively large num- 

 bers of opaque margined otoliths in the months out- 

 side the period of their maximum occurrence during 

 peak spawning can be expected. These, however, ob- 

 scure the results of tracing the frequency of otolith 

 edges throughout the year compared with the more 

 clear-cut results from the more temperate North 

 American waters. 



The differences in length at age and theoretical 

 growth parameters between Trinidad, Brazilian, and 

 North American fish may result from different environ- 



