Wilson and Nieland: Reproductive biology of Sciaenops ocellatus 



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The temporal persistence of postovulatory follicles 

 in red drum ovaries was investigated in two captive 

 red drum that were induced to spawn by means of 

 photoperiod manipulation and gonadotropin injection 

 (Nieland, Wilson, and Thomas, unpubl. data). Postovu- 

 latory follicles at 16-hour postspawning showed defi- 

 nite signs of degeneration, yet were recognizable as 

 such and resembled those seen in many wild caught 

 females. However, postovulatory follicles at 24-hour 

 postspawning were extremely degenerate and had 

 assumed an aspect much like that of an atretic fol- 

 licle. Such a condition was rare in feral specimens; 

 thus, all identifiable red drum postovulatory follicles 

 were assumed to be less than 24 hours old. Post- 

 ovulatory follicles seen in histological material were 

 classified as early, late, or very late based on their 

 degree of degeneration. 



Relative investment of energy to reproduction of red 

 drum was assessed with gonosomatic indices (GSI) cal- 

 culated as GSI = (gonad weight/BW) x 100 (Nieland 

 and Wilson, 1993). Calculations of mean monthly GSI 

 exclude immature individuals of both sexes (Wilk et 

 al., 1990; Nieland and Wilson, 1993). Because the in- 

 crease in ovary mass, which occurs concomitantly with 

 oocyte hydration, does not reflect energy to be expended 

 in reproduction, females with hydrating oocytes were 

 also excluded from calculations of mean monthly GSI. 

 The Statistical Analysis System (SAS Institute Inc., 

 1985) was used for analysis of variance (ANOVA), maxi- 

 mum-likelihood analysis (PROBIT), and linear regres- 

 sion (GLM). Significance level for statistical analyses 

 was 0.05 unless indicated otherwise. 



Results 



A total of 3,351 red drum ( 1,585 males, 1,765 females) 

 were sampled for reproductive analysis. Of these, 

 both the intact gonad weight and BW necessary for 

 calculation of GSI were available for 2,859 mature 

 and 341 immature specimens. Data on ovarian his- 

 tology were compiled for 1,379 mature females and 

 123 immature females. Age at time of capture for 

 3,316 red drum for which otoliths were available 

 ranged from 1 to 36 years for males and from 1 to 39 

 years for females. Proportions of the younger age 

 classes were particularly high during our 1992 sam- 

 pling when 327 of 504 individuals were age 6 or less. 

 Total weight and FL ranges among all specimens 

 were 0.7-19.2 kg and 399-1,115 mm, respectively. 



Sex ratio 



Sex ratios for red drum were highly variable among 

 source and gear categories and between mature and 

 immature individuals within these categories (Table 



1). Among all specimens and all mature specimens, 

 females were predominant; however, immature 

 males exceeded immature females in number by two 

 to one. Females also outnumbered males among all 

 mature individuals taken by sportfishing, among 

 mature individuals caught incidentally with 

 lutjanids, and among those captured with haul seine. 

 Conversely, males were more common among all 

 purse-seine specimens, all immature specimens, and 

 immature specimens taken by all methods except for 

 sportfishing. Sex ratios were not statistically differ- 

 ent from 1:1 for all mature red drum captured with 

 purse seines, for all taken incidentally with lutjanids, 

 and for those caught in gill nets. 



Seasonality 



Gonosomatic indices and ovarian histological data 

 indicated a potential 8—9 week red drum spawning 

 season beginning in mid August and extending into 

 October. Minimal GSI values for mature individuals 

 were found from January to July, averaging 0.26 for 

 males and 0.81 for females during these months (Fig. 

 1). Abrupt escalation of male and female GSI in Au- 

 gust signalled potential, if not certain, spawning ac- 

 tivity. Maximum GSI values were achieved in Sep- 

 tember followed by a return to near minimum levels 



