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Fishery Bulletin 92(4), 1994 



onstrates the effectiveness of this technique in as- 

 sessing onset and duration of spawning seasons. 



Determining the combination of environmental 

 factors which are the impetus for an August-October 

 red drum spawning season is beyond the scope of 

 this study. However, temperature data gathered at 

 a weather buoy located approximately 28 km south 

 of Biloxi, MS (lat. 30.1°N, long. 88.8°W) indicate that 

 seasonal mean sea surface temperatures ranged from 

 27.3° to 28.8°C and that daily mean sea surface tem- 

 peratures varied from 23° to 31°C during periods of 

 active spawning (National Climatic Data Center, 

 Asheville, North Carolina). Similar temperatures 

 have proven to be optimal in the spawning, hatch- 

 ing, and rearing of red drum in the laboratory (Arnold 

 et al., 1977; Roberts et al., 1978; Holt et al., 1981; 

 Arnold, 1988; Henderson-Arzapalo, 1992). 



Estimates of age and size at maturity for red drum 

 in the Gulf of Mexico, based largely on visual assess- 

 ment of gonadal development, show extensive varia- 

 tion. In his study of red drum in Texas waters, 

 Pearson ( 1929) perhaps originated the long held and 

 widely applied belief that few red drum of either sex 

 mature either before age 5 or before attaining 10 lb 

 (4.5 kg) and 700 mm. Among red drum populations 

 in Texas waters, maturity has been reported at 425 

 mm (Gunter, 1950), 625 mm (Miles 3 ), age 4 and 29.5 

 inches (750 mm) (Miles 4 ), and age 3 to 5 (Holt et al., 

 1981). For red drum off Mississippi, Overstreet 1 pro- 

 vided only a tabular compilation of the relation be- 

 tween standard length (SL) and gonad maturity 

 stages. These data were interpreted by Murphy and 

 Taylor ( 1990) to show 50% maturity in both sexes at 

 about 700 mm SL. Murphy and Taylor also presented 

 maturity schedules, which were based on histology 

 of ovaries and testes and gross appearance of each, 

 for red drum in Florida waters. They found fifty-per- 

 cent maturity of males at 529 mm FL and all males 

 mature at age 3; among females 50% and 100% matu- 

 rity occurred at 825 mm FL and 6 years, respectively. 



Given the maturity data cited above and that of 

 the present study, one might infer the existence of 

 geographical variation in maturity schedules among 

 red drum populations in the Gulf of Mexico. We de- 

 cline to discount this possibility. However, we sug- 

 gest that differences in methods of maturity assess- 

 ment and disparate definitions of maturity, especially 

 in females, confound comparisons. West (1990) re- 



3 Miles, D. W. 1950. The life histories of the spotted sea trout, 

 Cvnosewn nebulosus, and the redfish, Sciaenops ocellat us. Annu. 

 Rep. (1949-1950), Tex. Game and Fish Comm. Mar. Lab., p 

 66-103. Tex. Parks and Wildl. Dept., Austin. 



4 Miles, D. W. 1951. The life histories of the sea-trout, Cynoscion 

 nebulosus, and the redfish, Sciaenops ocellatus: sexual develop- 

 ment. Annu. Rep. 1 1950-1951 1, Tex. Game and Fish Comm. Mar. 

 Lab., 11 p., 2 figs., and 3 tables. Tex. Parks and Wildl. Dept., Austin. 



viewed methods of assessing ovarian development 

 in fishes and concluded that histology, though less 

 efficient in both cost and time, is less subjective than, 

 and preferable to, other methodologies. 



For the purposes of the present study, we defined 

 maturity in male red drum as the flow of milt from 

 the central lumen of the testis during the August- 

 October spawning season. The use of this subjective 

 definition may account for some of the discrepancy 

 in male maturity schedules between our study and 

 that of Murphy and Taylor (1990). 



However, for assessment of the maturity schedule 

 of female red drum in the northern Gulf we employed 

 a histologically objective benchmark definition: the 

 presence of vitellogenic oocytes in the ovaries of in- 

 dividuals captured during the spawning season. 

 Murphy and Taylor ( 1990) considered as mature only 

 those females of class 4 (late vitellogenesis) or greater 

 among their eight female reproductive classes in es- 

 timating an 825 mm FL at 50% maturity. This ne- 

 cessitated the categorization of out-of-season females 

 (their class 2) and of in-season females evidencing 

 early vitellogenesis (their class 3) as immature. The 

 former would not have been included in our analysis 

 of female maturity; the latter would have been clas- 

 sified as mature under our definition which precludes 

 judgments between early and late vitellogenesis. A 

 cautious re-interpretation of the tabular data in 

 Overstreet 1 would yield greater than 50% maturity of 

 females at 550-699 mm SL rather than the >700 mm 

 SL as stated by Murphy and Taylor (1990). Applying 

 our definition of maturity to Murphy and Taylor's data 

 would perhaps produce a length at 50% maturity more 

 in line with our estimate of 690-700 mm FL. 



Group-synchronous maturation of oocytes (Wallace 

 and Selman, 1981) and multiple, or batch, spawning 

 has been demonstrated in several species of sciaenid 

 fishes, including red drum (Fitzhugh et al., 1988). 

 Among these are queenfish, Seriphus politus 

 (DeMartini and Fountain, 1981); black croaker, Cheil- 

 otrema saturnam (Goldberg, 1981); white croaker, 

 Genyonemus lineatus (Love et al., 1984); spotted 

 seatrout (Brown-Peterson et al., 1988); and black 

 drum (Fitzhugh et al., 1993; Nieland and Wilson, 

 1993). For these and other such species, the stand- 

 ing crop of oocytes of some arbitrary size or of 

 vitellogenic oocytes gives little indication of the 

 individual's seasonal fecundity. Rather fecundity is 

 indeterminate and is the result of clutches of oocytes 

 matured and spawned periodically over the length 

 of the spawning season. Thus any estimate of sea- 

 sonal fecundity must consider the length of the 

 spawning season, the number of ova released in each 

 spawning event (batch fecundity), and the periodic- 

 ity of these spawning events (spawning frequency). 



