Roumillat and Brouwer: Reproductive dynamics of Cynosc/on nebulosus 



485 



over the entire range of maturation and to select only 

 those clearly showing nuclear migration (based on his- 

 tological observations) ensuring that only oocytes in the 

 same phase of FOM (Brown-Peterson et al., 1988) were 

 included in RF calculations. If sampling is conducted 

 during a time period that is not close to active spawning 

 (i.e., when oocytes are in different phases of FOM), then 

 the number of oocytes per gram may be miscalculated. 



As with BF, our RF estimates were higher than those 

 reported for seatrout in the Gulf of Mexico (Brown- 

 Peterson et al., 1988; Brown-Peterson and Warren, 

 2001), although spotted seatrout reproductive para- 

 meters appeared to vary considerably even within the 

 Gulf of Mexico (Brown-Peterson et al., 2002). This was 

 attributed to differential environmental conditions or 

 food availability (or to both) (Brown-Peterson and War- 

 ren, 2001; Brown-Peterson et al., 2002). The significant 

 seasonal increase in RF that we observed for spotted 

 seatrout in South Carolina, however, has not been re- 

 ported elsewhere. Brown-Peterson et al. (1988) found no 

 differences in mean monthly RF among spotted seatrout 

 in Texas. Brown-Peterson and Warren (2001) found sig- 

 nificantly higher RF values in June than in August. In 

 both instances, however, a small sample size may have 

 biased their results. 



Comparisons of mean oocyte diameters among months 

 related the increase in RF to a general decrease in 

 oocyte size over the course of the season. This phenom- 

 enon is widespread among marine pelagic spawners, 

 and scientists have put forth several explanations to 

 account for it (see Chambers, 1997). Bagenal (1971) sug- 

 gested that egg size decreased over the spawning sea- 

 son owing to concurrent increased food availability for 

 larvae. Others have suggested an inverse relationship 

 between temperature and egg size (Ware, 1975; Woot- 

 ton, 1994; Miller et al., 1995) or a seasonal decrease in 

 egg size that is correlated to the condition of spawning 

 females (DeMartini and Fountain, 1981; Chambers and 

 Waiwood, 1996). The latter seems to apply to spotted 

 seatrout in this study because a diminishing trend 

 through the spawning season was observed in the con- 

 dition factor of females. 



Annual fecundity 



Brown-Peterson (2003) presented AF estimates for spot- 

 ted seatrout throughout their range. Our estimates were 

 substantially below those for spotted seatrout in Indian 

 River Lagoon (Crabtree and Adams 7 ) but approximated 

 those of Lowerre-Barbieri et al. 8 for trout in Georgia. A 

 possible reason for the higher values in Florida was the 

 more protacted spawning season in that area (50 days 

 longer). No comparisons of AF estimates presented in 

 this study and those of spotted seatrout in the Gulf of 

 Mexico (Brown-Peterson, 2003) were made because they 

 were not specific to age classes. 



The main impetus behind the present study was to 

 establish annual fecundity (AF) estimates by age class. 

 We found that age-1 through age-3 spotted seatrout 

 occurred abundantly in SC estuaries and that each of 



these age cohorts showed unique fecundity dynamics. 

 The AF for an average age-1 fish was one-third that of 

 age-2 (-3.28 million vs. 9.5 million). One year-old fish, 

 however, constituted the majority offish in our samples; 

 their abundance was twice that of 2-year-olds and seven 

 times that of 3-year-old fish. Even though the average 

 age-3 trout produced almost twice as many oocytes dur- 

 ing the season (17.5 million) as the average age-2 fish, 

 their reduced abundance in our estuaries made their 

 overall contribution only half that of 2 year-olds. Ages 

 4 and 5 were estimated to produce approximately 24.4 

 million and 31.6 million oocytes per female, respective- 

 ly; however, the oocyte production by the predominant 

 age groups overshadowed theirs. When analyzed in re- 

 lation to the occurrence of the other age classes in our 

 estuaries, age-2 fish contributed the greatest number of 

 fertilizable oocytes to the environment (39%). 



Reliable fecundities based on age and on length are 

 optimal for stock assessment models (Williams 9 ). This 

 study provided AF estimates for three age classes that 

 can be used in age-based models for the spotted seat- 

 rout population in South Carolina. Annual fecundity 

 estimates based on length, however, have not been at- 

 tempted even though length appears to be the best pre- 

 dictor of fecundity in spotted seatrout (see references in 

 Brown-Peterson, 2003). Further analyses to investigate 

 the relationship between egg production and fish length 

 for each month of the spawning season would allow for 

 more precise management efforts based on individual 

 length-based estimates of AF. 



Acknowledgments 



We thank members of the Inshore Fisheries Section of 

 the South Carolina Department of Natural Resources for 

 assisting in field data collection throughout this study 

 (C. Wenner, J. Archambault, H. von Kolnitz, W. Hegler, 

 E. Levesque, L. Goss, C. McDonough, C. Johnson, A. 

 Palmer). C. Wenner, H. von Kolnitz, and E. Levesque 

 conducted age assessments. Histological processing was 

 provided by C. McDonough, R. Evitt, A. Palmer, and 

 W. Hegler. Assistance with oocyte counts was provided 

 by C. McDonough, T. Piper, K. Maynard, and R. Evitt. 

 Data management was coordinated by J. Archambault, 

 C. Wenner, E. Levesque, and three anonymous reviewers 

 provided helpful suggestions on the manuscript. Funding 

 for this study was provided by the National Marine Fish- 

 eries Service under MARFIN grant no. NA77FF0550. 



Literature cited 



Bagenal. T. B. 



1971. The interrelation of the size offish eggs, the date 

 of spawning, and the production cycle. J. Fish. Biol. 

 3:207-219. 



;l Williams, E. 2003. Personal commun. National Marine 

 Fisheries Service, 101 Pivers Island, Rd., Beaufort, NC 

 28516. 



