Cuellar et al.: Reproductive seasonality, maturation, fecundity, and spawning frequency of the vermilion snapper 



651 



mined. Because of these limitations the spawning- 

 frequency estimate calculated in this study should 

 be considered preliminary. More detailed work needs 

 to be done to calculate a more representative spawn- 

 ing-frequency estimate for the population in this re- 

 gion. Additional work should include sampling over a 

 24-h period for a series of days during the spawning 

 season to define POF age from a larger number offish. 



In spite of limitations, a preliminary estimate of 

 spawning time and POF duration can be derived from 

 the literature and our observations. Postovulatory 

 follicles in Lutjanus vittus persist for only about 24 h 

 (Davis and West, 1993), and POF's in vermilion snap- 

 per may be similar in duration owing to the higher 

 temperature of shelf waters during the spawning 

 season, which may accelerate reabsorption of POF's 

 (Hunter and Macewicz, 1985). Most lutjanids ap- 

 peared to spawn at dusk ( Wicklund, 1969; Starck and 

 Schroeder, 1971; Thresher, 1984) but recently some 

 lutjanids were found to spawn in the mid-afternoon 

 (Davis and West, 1993; Carter and Perrine, 1994). 

 In addition, vermilion snapper are nocturnally ac- 

 tive (Grimes, 1979; Sedberry and Cuellar, 1993); thus 

 spawning activity may continue into the night. In 

 the present study, some vermilion snapper appeared 

 to spawn from mid-afternoon to early dusk, as do 

 other lutjanids; when the majority spawn was not 

 determined. 



A comparison of the sex ratio, based on present 

 data and Grimes ( 1976), indicated that the sex ratio 

 of vermilion snapper had not changed in 20 years 

 (62.6 and 62.5% females, respectively). Sex ratios for 

 western Atlantic snappers often deviate from 1:1, 

 with males outnumbering females in more cases than 

 the reverse (Grimes, 1987). MARMAP data collected 

 with standardized methods over a 15-yr period re- 

 vealed an increase in the percentage of females in 

 the vermilion snapper population in the region from 

 about 60% in 1978-79 to about 72% in 1991-93 (Zhao 

 and McGovern 1 ). This change in sex ratio has oc- 

 curred in spite of no significant difference in fishing 

 mortality (F) between males and females (Zhao and 

 McGovern 1 ). Temperature changes have been known 

 to induce change in sex ratio in fish (Lagomarsino 

 and Conover, 1993) but summer water temperatures 

 on the middle and outer continental shelf off the 

 southeastern United States have been remarkably 

 uniform for the 17 years preceding this study (Na- 

 tional Environmental Satellite, Data, and Informa- 

 tion Service 5 ). Decreases in mean size of vermilion 



5 National Environmental Satellite, Data, and Information Ser- 

 vice. 1992. Oceanographic monthly summary, July 1978-July 

 1992. U.S. Dep. Commer., National Ocean Service, National 

 Weather Service. Ocean Products Division, Camp Springs, MD. 



snapper in recent years are well documented (Collins 

 and Sedberry, 1991; Zhao and McGovern 1 ). This 

 change in size may be caused by intense fishing, 

 which is believed to have resulted in fewer individu- 

 als and smaller fish size (Collins and Pinckney, 1988; 

 Bas andCalderon-Aguilera, 1989; Sutherland, 1990) 

 and, hence, reduced fecundity (PDT, 1990). Unknown 

 compensatory mechanisms may be at work under the 

 intense selection pressure exerted by fishing on ver- 

 milion snapper; these mechanisms may result in al- 

 tered sex ratios to compensate for reduced individual 

 fecundity. 



All vermilion snapper in this study were mature, 

 with the smallest fish measuring 186 mm total length 

 (TL). The smallest aged fish was two years old at 

 186 mm TL. Grimes (1976) found most mature fish 

 at age three were 186-256 mm TL and at age four 

 were 256-324 mm TL; only a few individuals ma- 

 tured in their second year at approximately 150 mm 

 TL. After age four, vermilion snapper in our study 

 were much smaller than those in the study by Grimes 

 ( 1976). The size difference could, again, be explained 

 by increased fishing pressure or by the fact that 

 Grimes (1976) used scales and whole otoliths, not 

 sectioned otoliths, to determine age. Collins and 

 Pinckney (1988), like Grimes (1976), used scales 

 rather then sectioned otoliths and found that 60% of 

 females and 90% of males mature at 160 mm TL. 

 Recently, Zhao and McGovern 1 found mature vermil- 

 ion snapper at an even a smaller size, with 100% of 

 males and females mature at 140 mm TL. This 

 change in size at maturity may be a result of fishing 

 pressure. 



Vermilion snapper has a protracted spawning sea- 

 son throughout the summer months in the south- 

 eastern United States. The gonad index used by 

 Grimes (1976) indicated that vermilion snapper in 

 this area spawn from late April to September. In the 

 Carolinas and Georgia, Powles (1977) and Fahay 

 ( 1975 ) found high abundances of larvae during July- 

 September, although they did not sample beyond that 

 period of time. Nelson (1988) and Collins and 

 Johnson 4 found that the spawning season of vermil- 

 ion snapper occurred during spring and summer in 

 the Gulf of Mexico. Also in the Gulf of Mexico, Comyns 

 and Lyczkowski-Shultz 3 indicated that spawning 

 occurred from May through September on the basis 

 of abundance of larvae. However, in Puerto Rico, 

 Boardman and Weiler (1979) found that vermilion 

 snapper spawned year round, and Munro et al. (1973) 

 found a ripe female vermilion snapper in November 

 in Jamaica. Restricted spawning and year-round 

 spawning in the same species may reflect a differ- 

 ence between temperate and tropical locations, or as 

 Grimes (1987) suggested, a difference between con- 



