364 



Fishery Bulletin 97(2), 1999 



The von Bertalanffy model L, = LJ 1 - e"*" " '»') was 

 also used to describe the relation between length and 

 age. Relative ages were assigned to fish by using a 

 birth date of 1 April based on trends in gonadoso- 

 matic indices and the regression of sagittal weight on 

 month of capture for young-of-the-year fish.^ Von 

 Bertalanffy growth parameter estimates for males and 

 females were compared by using a likelihood ratio test 

 at a = 0.05 (r statistic) (Cen-ato, 1990; Kimura, 1980). 



Results 



Length and weight 



Greater amberjack ranged from 167 to 1441 mm (FL); 

 females ranged from 374 to 1441 mm ( .r =879 mm), 

 and males ranged from 387 to 1203 mm ( .v =854 mm). 

 Females represented 72% of the fish over 1 m in fork 

 length. There was no significant difference in mean 

 fork length between males and females. Females 

 ranged from 0.82 to 42.5 kg (.r=11.33) and males 

 ranged from 0.85 to 28.8 kg ( .r =9.90). Mean gutted 

 weight (GW) of females was significantly gi'eater than 

 that of males (ANOVAP>F= 0.03) and females repre- 

 sented 789c of the fish over 20 kg gutted weight. Re- 

 gi'essions for TL versus FL and TW versus GW were 



Females: 



Males: 



Sex unknown: 



W= 3.25 X 10-5 ^2 87 (,.2=0.98, n=324) 



W =1.75x10-^1^^^ 

 W=7.62xlO-5L-8' 



(n=0.98,n = 184i 

 (r2=0.98, «=354) 



Otolith structure 



TL = 1.14 i^L + 13.05 

 TW = 1.09 GW+ 119.40. 



(r'-=0.99) 

 (r-=0.99) 



Monthly mean fork length and sex ratio from 

 charterboat catches were compared because this was 

 the only year-round source of greater amberjack 

 (Table 1). Charterboats fishing Gulf of Mexico wa- 

 ters off the Louisiana coast caught larger greater 

 amberjack during the summer months (from May to 

 September) and smaller greater amberjack during 

 winter months (from November to February). Sex 

 ratios ranged from 0.4:1 to 4.5:1 (x=2.49) (Table 1), 

 and there was a relatively greater abundance of fe- 

 males each month except September. 



The relation between fork length (cm) and gutted 

 weight (kg) was best described by a power function. 

 The slopes of the regression lines for males and fe- 

 males were significantly different. The equations 

 explaining these relations were 



All samples: W= 4.2 x 10-^ L-'^'' (7-2=0. 99. «=862) 



' Thompson, B. A.. C. A. Wil.son, .) H KcndiT, M Beasley, and C. 

 Cauthron. 1992. Age, growth, and reproductive biology of 

 greater amberjack and cobia from Louisiana waters. Final re- 

 port to U.S. Department of Commerce, Marine Fisheries hiitia- 

 tive (MARFIN) Program, NMFS, St. Petersburg, FL, NA90AA-H- 

 MF722, 77 p. 



Greater amberjack sagittae are small, thin, fragile, 

 and elongate in the anterior direction and bluntly 

 crenelate at the posterior end. The medial surface is 

 convex and has a deep, prominent sulcus. The ante- 

 rior portion of the sagitta is cui-ved laterally and the 

 posterior end is relatively flat. The rostrum is longer 

 than the antirostrum, but the difference increases 

 with fish size. Prominent grooves and ridges are 

 present on the lateral side of the sagittae and are 

 nearly absent on the medial side (Fig. 1). The 

 asteriscus and lapillus were much smaller and more 

 fragile than the sagittae and have no annuluslike 

 external or internal growth features. The small size 

 and fragility of these smaller otoliths, as well as the 

 time and care required to remove them, precluded 

 additional sampling. 



Greater amberjack sagittae weights ranged from 

 1.4 to 68.6 mg. The mean weight of male sagittae 

 (23.2 mg) was not significantly different from that of 

 females (25.0 mg). The relationship between FL and 

 sagittal weight (SW) was best described with a nega- 

 tive exponential (following the von Bertalanffy equa- 

 tion). Because there was no difference in this rela- 

 tion between males and females {P>x^>0.Q5 ) the data 

 were combined to produce the equation (Fig. 2) 



FL 



s\v 



151 (1-e 



-0 04iS\V +1.61 1 V 



(r2=0.96) 



