844 



Fishery Bulletin 92|4), 1994 



MM 

 I 



JSNJMMJSNJMMJSNJMMJSNJMMJSNJMMJSN 

 986 | 1987 | 1988 | 1989 | 1990 | 1991 



JMMJS 

 | 1992 | 



Month/Year 



Figure 1 



Mean monthly gonosomatic indices for mature male 

 (n=l,306) and female (rc = l,553) red drum from the north- 

 ern Gulf of Mexico. Sample sizes for months during which 

 red drum were available varied from 1 to 110 for males 

 and from 1 to 183 for females. Absence of vertical bar for 

 either sex indicates that no specimens were sampled dur- 

 ing the month and year indicated below. Narrow vertical 

 bars at tops of GSI bars indicate +1 standard deviation 

 (SD) from mean value (plotted only for those months when 

 SD>0.5). 



in October. Our data, collected over more than six 

 years, demonstrated a single annual GSI maximum 

 (ranging from 4 to 8) in each sex. 



Red drum ovarian tissues undergo an annual cycle 

 of oocyte maturation and recrudescence coincident 

 with the female GSI cycle. Over the entire study 

 duration, oogonia and primary growth oocytes were 

 present in varying numbers in all ovary samples but 

 were virtually ubiquitous from January through June 

 (Fig. 2). Recrudescence and maturation of primary 

 growth oocytes to the cortical alveoli and vitellogenic 

 stages, indicative of preparation for spawning, was 

 seen in July. Maximum numbers of maturing 

 vitellogenic and mature hydrated oocytes were found 

 during August and September. Declines in numbers 

 of cortical alveolar and vitellogenic oocytes and con- 

 comitant increases in numbers of primary growth 

 oocytes occurred in October suggesting the cessation 

 of spawning activity at this time. Although we have 

 few data from November and December, primary 

 growth oocytes are assumed to constitute nearly 

 100% of the oocyte population during these months. 



Among all spawning seasons, the onset of spawn- 

 ing activity, evidenced by the first observation of yolk 

 coalescence (late vitellogenesis) or postovulatory fol- 



licles in ovarian histological samples, ranged from 

 14 August to 18 August. Atretic states 2 and 3, 

 indicative of cessation of spawning, became in- 

 creasingly common from late September through 

 early October. When we were able to extend our 

 sampling in 1987 and 1988, 100% atresia of 

 vitellogenic oocytes was realized by the end of 

 October indicating completion of spawning at this 

 time. 



Age, length, and weight at maturity 



The onset of sexual maturity in both male and fe- 

 male red drum in the northern Gulf of Mexico is 

 variable with respect to age. Estimates of percent 

 maturity at age are comparable and increase at 

 much the same rate for both sexes, the only major 

 discrepancies occurring at age 2 and age 5 (Table 

 2). Greater than 50% maturity is achieved in both 

 sexes at age 4. All males and all females are ma- 

 ture at age 5 and age 6, respectively. 



Sexual maturity in red drum is similarly unre- 

 lated to size of the individual (Table 2). Fork length 

 and TW minima among mature female red drum 

 were 598 mm (age 4, 4.18 kg) and 3.43 kg (age 3, 

 675 mm). Maximum-likelihood analysis (PROBIT 

 analysis, Murphy and Taylor, 1989) of 10 mm in- 

 crements and of 0.10 kg increments indicated 50% 

 maturity is achieved at 690-700 mm and 4.00- 

 4.10 kg. All females greater than 810 mm and 6.10 

 kg were mature. 

 Male red drum from the northern Gulf of Mexico 

 mature at somewhat lesser length and weight than 

 do females; however, sex-specific percent maturities 

 at size become roughly equivalent at 750-700 mm 

 and 5.00-5.49 kg (Table 2). Fork length and TW 

 minima for mature males were 593 mm (age 5, 2.56 

 kg) and 2.35 kg (age 2, 615 mm). Fifty percent matu- 

 rity (maximum-likelihood analysis as above) occurred 

 at 660-670 mm and 3.40-3.50 kg and all males 

 greater than 810 mm and 5.40 kg had matured. 



We observed no instances of decreased or arrested 

 gonadal development among older individuals. Red 

 drum of both sexes appear to be fully capable of re- 

 productive activity from the onset of maturity until 

 death. 



Batch fecundity 



Fitzhugh et al. (1988) reported significant ovarian 

 location effects in their estimates of red drum batch 

 fecundity. To test the precision of our estimates within 

 individuals, replicate samples (30-60 mg) of ovarian 

 tissue from each of six ovarian regions (anterior, 

 medial, and posterior of both right and left lobes) 

 were removed from six hydrated females captured 



