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Fishery Bulletin 92(4). 1994 



4) to estimate batch fecundity and spawning fre- 

 quency of red drum from the neritic waters of the 

 northern Gulf of Mexico. 



Methods and materials 



Red drum were sampled in the neritic waters of the 

 northern Gulf of Mexico (Mobile Bay, Alabama west- 

 ward to Galveston Bay, Texas) from March 1986 

 through September 1992, a period spanning seven 

 spawning seasons. Various aspects of the reproduc- 

 tion of those specimens taken from March 1986 

 through November 1986 have been previously re- 

 ported by Fitzhugh et al. (1988). The availability of 

 red drum during this study was sporadic and gener- 

 ally limited by federal and state restrictions on both 

 the commercial and recreational fisheries in the Gulf 

 of Mexico. Although the vast majority of specimens 

 were taken by purse seine, the strategies used to lo- 

 cate red drum schools for capture varied among years. 

 Prior to the closure of the Exclusive Economic Zone 

 to all red drum harvest in 1986, specimens came from 

 the commercial purse-seine fishery. Red drum col- 

 lected from July 1986 through 1988 were taken con- 

 currently with a National Marine Fisheries Service 

 tag-recapture investigation. Their methodology simu- 

 lated a commercial purse-seine fishery and used spot- 

 ter airplanes to locate schools at the surface. Since 

 August 1989 most red drum were taken incidentally 

 in the directed purse-seine harvest of blue runner, 

 Caranx chrysos, detected visually at the surface. 



The above samples were supplemented with speci- 

 mens from sportfishing tournaments, from inciden- 

 tal catches of vessels targeting snappers ( Lutjanidae), 

 and from gillnet and haul-seine catches. These 

 sources were sampled as circumstances allowed to 

 permit tracking of ovarian development and 

 gonosomatic indices during those months when speci- 

 mens taken by purse seine were not available. 



Protocols for the collection of morphometric data 

 (fork length [FL] in mm, total weight [TW] in kg, 

 eviscerated body weight [BW] in kg), processing of 

 ovaries for histological examination, and enumera- 

 tion of oocyte maturation stages from histological 

 slides (Wallace and Selman, 1981; Fitzhugh et al., 

 1988 ) are given in Nieland and Wilson ( 1993). Histo- 

 logical slides were also scanned for the presence of 

 yolk coalescence, and for postovulatory follicles and 

 atretic follicles. Ages of individuals were estimated 

 from sagittal otoliths as described in Beckman et al. 

 (1988). Their methodology assumed a biologically 

 reasonable hatching date of 1 October; however, for 

 our purposes age estimates were calculated with 1 

 August as the arbitrary red drum hatching date. This 



modification allows all members of a cohort to be 

 assigned the same integer year age. 



Sexual maturity of females captured during the 

 spawning season was defined as the progression of 

 oocyte maturation to vitellogenesis (Brown-Peterson 

 et al., 1988; Nieland and Wilson, 1993). Milt flow from 

 the central lumen of the testes produced by gentle 

 squeezing indicated sexual maturity in males simi- 

 larly taken during the spawning season (Pearson, 

 1929; Brown-Peterson et al., 1988; Murphy and Tay- 

 lor, 1990; Nieland and Wilson, 1993). 



Only those red drum females captured by purse 

 seine were included in calculations of spawning fre- 

 quency and batch fecundity. Batch fecundity was 

 estimated gravimetrically from fresh ovarian weights 

 for 51 females exhibiting overt macroscopic and mi- 

 croscopic hydration of oocytes with the hydrated oo- 

 cyte method (Hunter and Goldberg, 1980; Hunter et 

 al., 1985). Seasonal spawning frequencies were esti- 

 mated with two different methods after examination 

 of 572 ovaries collected during the spawning seasons. 

 The postovulatory follicle method (Hunter and 

 Goldberg, 1980; Hunter and Macewicz, 1985; Hunter 

 et al., 1985; Brown-Peterson et al., 1988; Nieland and 

 Wilson, 1993) uses the number of mature females 

 with postovulatory follicles to determine a spawn- 

 ing fraction or that proportion of the female spawn- 

 ing population that spawned the previous day. The 

 inverse of the spawning fraction, the spawning fre- 

 quency, is the average number of days over which 

 each reproductively active female will spawn once. 

 The spawning frequency estimates of Fitzhugh et al. 

 (1993), referred to as the "time-calibrated" method, 

 are based on a time-course of final oocyte matura- 

 tion for black drum, Pogonias cromis, and another 

 sciaenid species, the spotted seatrout, Cynoscion 

 nebulosus, (Brown-Peterson et al., 1988). This meth- 

 odology calculates proportions of day-0 females (im- 

 minent spawners evidenced by oocyte yolk coales- 

 cence or hydration) and day-1 spawners (previous 

 spawners evidenced by postovulatory follicles) in the 

 female spawning population. The average of the pro- 

 portions of day-0 and day-1 females yields a spawn- 

 ing fraction which is inverted to produce spawning 

 frequency as defined above. Note that females spawn- 

 ing on consecutive days will be classified as both day- 

 and day-1 individuals. Also those females evidenc- 

 ing oocyte atresia states 2 (atresia of >509r of vitel- 

 logenic oocytes) and 3 (atresia of 100% of vitellogenic 

 oocytes) (Fitzhugh et al., 1993) were not included in 

 either estimate of spawning frequency. Both condi- 

 tions, usually encountered at the end of the spawn- 

 ing season, indicate a zero probability of future 

 spawning and an effective exit from the spawning 

 population (Hunter and Macewicz, 1985). 



