Fitzhugh et al.: Reproductive biology of Pogonias cromis in Louisiana 



249 



We estimated spawning frequency by examining 

 ovarian tissues of 193 mature females (vitellogenic oo- 

 cytes present) sampled over the spawning season. We 

 define spawning season as the period during which 

 spawning condition was histologically evident, from 

 first evidence of coalescence of vitellogenic oocytes on 

 11 November 1986, until atresia of vitellogenic oocytes 

 was occurring in all females encountered on 12 May 

 1987 (Table 2). The numbers of day-0 and day-1 spawn- 

 ing females was 80 and 40 (frequencies = 0.415 and 

 0.207) for this period, respectively. This resulted in an 

 overall seasonal frequency of 0.311, or each female 

 spawning on average once every 3d (Table 2). From 

 November 1986 through May 1987, 50 of 193 females 

 (26%) contained POFs. This method of estimating 

 spawning frequency would correspond to a spawning 

 frequency of once every 4d, or a total of 46 times, 

 during the spawning season. 



Batch fecundity 



We determined batch fecundity for 25 visibly-hydrated 

 females which possessed no recent POF in histological 

 sections that would indicate egg shedding. The range 

 in batch fecundity was 7.4xl0 5 hydrated oocytes for a 

 4.3kg female, to 3.8X10 6 hydrated oocytes for a 4.8kg 

 female, indicating wide variation in fecundity based 

 on body size (Fig. 4). The number of hydrated oocytes/ 

 g of ovary weight ranged from 1046 to 4902. Based 

 on eviscerated body weight, the number of eggs/g 

 ranged from 131 to 793. The mean value for batch 



4000 6000 8000 



Gutted Body Weight (g) 



10000 



Figure 4 



Batch fecundity and eviscerated body weight with 95 r /r confidence i 

 terval for hydrated female black drum Pogonias cromis, sampled 

 February and March 1987. 



fecundity was 1.6xl0 6 for a mean eviscerated weight 

 of 6. lkg. 



Location of tissue samples 



Black drum possess relatively large gonads for teleosts, 

 and we sampled ovaries weighing 0.4-1.6 kg laden with 

 hydrated oocytes. No significant differences were de- 

 tected between positions within a lobe or between 

 right and left ovarian lobes for number of hydrated 

 oocytes/g of ovarian tissue (Table 3). However, counts 

 of hydrated oocytes/g were lower for the anterior posi- 

 tion (jc 1780) than for either mid- or posterior ovarian 

 regions (x 2013 and 1928, respectively) (Table 3). 



Discussion 



We noted differences in sex ratios between samples 

 collected by various fishing gears during the period of 

 reproductive development and spawning, November- 

 May. Landings by offshore trawlers (where spawning 

 females were found in February and March) were 

 clearly dominated by males. Females dominated in in- 

 shore samples from all gears (primarily gillnet and 

 haul-seine landings), but this female dominance was 

 not as prevalent outside the breeding season during 

 October, June, and July. These divergent ratios sug- 

 gest sexes are spatially segregated for periods during 

 the reproductive season. This difference in sex ratios 

 has been noted in other fisheries where a higher pro- 

 portion of males attend those females in ac- 

 tive spawning condition on the spawning 

 grounds (DeMartini & Fountain 1981, Hunter 

 & Goldberg 1980). 



In a synthesis of previous studies, Simmons 

 & Breuer (1962) reported age-at-maturity for 

 black drum to be 2 yr at 320 mm based on scale 

 increments, length frequencies, and gross as- 

 sessment of ripe females (granular roe ob- 

 served) in Texas waters. Pearson (1929) found 

 drum as small as 270 mm with developing ova- 

 ries. Murphy & Taylor (1989) provide evidence 

 for larger sizes-at-maturity, with males ma- 

 turing at 590 mm (4-5yr old) and females ma- 

 turing at 650 mm (5-6 yr old). Our findings of 

 age-at-maturity agree with Murphy & Taylor's 

 (1989) estimates. Mature females and males 

 occurred at a size-range of 600-640 mmFL, cor- 

 responding to ages 3-8 yr (Beckman et al. 

 1990). A mature female with hydrated eggs 

 was observed as small as 625 mmFL; this 

 indicates that size- or age-at-maturity for 

 northern Gulf of Mexico stocks is greater than 

 previously estimated by Simmons & Breuer 



