FISHERY BULLETIN: VOL. 78. NO. 1 



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MONTHS 



Figure 2. — Monthly mean gonad index of female vermilion 

 snapper collected from May 1972 to April 1974, mean bottom 

 temperatures at collecting sites, and photoperiod (U.S. Depart- 

 ment of Commerce 1971, 1972, 1973). 



monthly mean gonad index is well correlated with 

 lengthening photoperiod and increasing bottom 

 temperature. 



The seasonal occurrence of juveniles and the 

 large size variation within the youngest age-group 

 provides additional evidence of an extended sum- 

 mer spawning season. During October and 

 November 1973, several hundred juveniles rang- 

 ing from 53 to 227 mm TL were trawled in Long 

 Bay, N.C. and S.C., and also off Charleston. Aging 

 of these fish from scales showed the sample to 

 contain mostly age-groups and 1. Using the 

 growth rate for the first year of life (Grimes 1978) 

 for extrapolating backwards, we determined that 

 the age fish collected in October and November 

 1973 were spawned throughout the summer 

 months. 



Although actual spawning was never observed, 

 it probably occurs around rough bottom from 31 to 

 91 m but may be more concentrated in deeper 

 areas (55-91 m). Ripe fish were taken over rough 

 bottom at depths of 31-91 m when bottom temper- 

 atures were 20.6°-24.8° C. In Raleigh Bay and 

 northern Onslow Bay, ripe fish were more abun- 

 dant from 55 to 91 m; however, in the southern 

 portion of the study area (southern Onslow Bay 



and Long Bay) ripe individuals were more equally 

 distributed with depth. 



Reproductive synchrony within schools may be 

 indicated by hook-and-line sampling. Fish were 

 usually caught in sudden bursts of fishing activity; 

 seldom were single individuals encountered. 

 Gonad indices for fish of similar size caught over a 

 short time interval (probably from the same 

 school) were nearly identical, indicating that re- 

 production within schools may be highly syn- 

 chronized. 



Multiple spawnings each season are indicated 

 by the relative abundance of ova types (described 

 earlier) at different times during the spawning 

 season (Table 2). Maturing ova were present April 

 through October and spawning apparently takes 

 place during this period. Early in the spawning 

 season (May) all three developing ova types were 

 present in considerable abundance. When ripe ova 

 were present later in the season (June or July), 

 fewer smaller developing ova occurred. In August 

 and September (late in the spawning season) when 

 ripe ova were present, smaller developing ova 

 were absent. The total of the developing ova types 

 may represent all that will be spawned that sea- 

 son, and at each spawning a female develops only 

 as many ova as her abdominal capacity will allow. 

 This process could be repeated a number of times 

 during the season until all eggs are spawned. 



Variation in gonad index during the spawning 

 period for similar size fish may also indicate frac- 

 tional spawning. This was evident during the 

 spawning months of 1972 and 1973 when the 

 gonad index of both males and females of similar 

 size varied by as much as a factor of 12 (Figure 3). 

 The small size of ripe gonads combined with high 

 fecundity (see subsequent discussion) is additional 

 evidence for fractional spawning. The mean per- 

 cent of body weight (observed) for ovaries of ma- 

 ture females collected during spawning months 

 was 2.4% (0.6-5.8%, n = 40). Mature males had 

 testes averaging 1.1% of body weight (0.4-2.4%, n 

 = 15) during the same months. Also, we fre- 

 quently observed semiflacid ovaries with no loose 

 ova (perhaps partially spawned) in large adult 

 females from June through September. 



Maturation 



Age and growth data of Grimes (1978) and our 

 reproductive data indicate that most fish attain 

 sexual maturity during their third or fourth years 

 of life (186-256 and 256-324 mm TL), but a few 



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