FISHERY BULLETIN: VOL. 78. NO. 1 



Several authors report fractional spawning in 

 marine fishes (Starck and Schroeder 1971; 

 Beaumarriage 1973; de Silva 1973; Macer 1974). 

 Our inference that variation in gonad index dur- 

 ing a spawTiing month for similar size fish 

 suggests fractional spawning is supported by 

 Starck and Schroeder's (1971) findings on a re- 

 lated species, Lutjanus griseus, the gray snapper. 

 They concluded, from variation of ovary lengths 

 and weights from fish of similar size, that spawn- 

 ing probably occurs more than once in the same 

 season in south Florida waters. 



In the results, we described three types of 

 maturing ova and concluded that they indicate 

 fractional spawning, yet the most mature ova type 

 was found only in a few ripe-appearing females. 

 Evidently final ova maturation occurs nearly 

 simultaneously with spawTiing so that the proba- 

 bility of catching a completely ripe fish is low. 



Maturation 



There are no published reports on maturation in 

 vermilion snapper, but Starck and Schroeder's 

 (1971) results on gray snapper agree closely. They 

 wrote that females are mature at age 3 and 190- 

 200 mm SL. Results for vermilion snapper also 

 agree with Starck and Schroeder's findings thatL. 

 griseus females >375-400 mm SL probably spawn 

 more times each year than smaller ones, and Mos- 

 ley (1966) observed (from a sample offish 223-456 

 mm SL) that early in the spawning season, small- 

 er red snapper, L. campechanus, showed less 

 gonad development than larger ones, perhaps in- 

 dicating earlier spawning by larger fish. Also 

 similar to our results, Quast ( 1968) showed earlier 

 and longer seasonal gonad maturation with 

 growth in kelp bass. 



Earlier spawning by older fish can probably be 

 explained via the interplay between somatic and 

 gonad growth and maintenance. Sexual maturity 

 marks diminished growth in many fishes (Hubbs 

 1926; Magnuson and Smith 1963; lies 1974). 

 Female vermilion snapper older than 5 yr (390 

 mm TL) are beyond the years of most rapid somat- 

 ic grov^fth (Grimes 1978) and undoubtedly can af- 

 ford to put more energy into gonad development, 

 even though the energy costs of maintenance are 

 greater for ^arger fish as well. 



Cohen (1&76), using a theoretical mathematical 

 model, predicts that if reproductive success de- 

 pends upon maximizing reproductive biomass, the 

 change in the fraction of reproductive growth (di- 



144 



minished somatic growth and beginning repro- 

 ductive growth) will occur at a time and mass just 

 prior to maximum growth rate. We used annual 

 length increments and a length-weight relation 

 (Grimes 1978) to derive annual increments in 

 mass, so that we could evaluate how well vermil- 

 ion snapper fit the optimal timing of reproduction 

 model. The greatest annual growth increment 

 (weight) occurs between age 6 and 7. Age 5, then, 

 is the year of life the model predicts the growth 

 change, and Figure 5 shows that fish age 5 and 

 older reflect the growth change by maturing ear- 

 lier and being mature for a longer time each re- 

 productive season. 



Sex Ratio 



The literature on other lutjanids provides little 

 help in interpreting our findings that sex ratios of 

 vermilion snapper vary significantly from 1:1 

 overall, and throughout life (as measured by 

 length). Camber's (1955) data on red snapper 

 showed a greater proportion of males when small 

 (200-400 mm TL) but a higher percentage of 

 females among larger fish (400 mm TL). Mosley 

 (1966) reported 56% males and 44% females 

 among red snapper (200-400 mm TL). Bradley and 

 Bryan (1974), however, reported a 1:1 ratio for 

 1,129 adult red snapper (no size range reported), 

 and Starck and Schroeder (1971) gave a 1:1 ratio 

 for 772 gray snapper (including small juveniles to 

 adults). 



Wenner (1972) suggested several possibilities to 

 account for unequal sex ratios (i.e., differential 

 mortality, growth, and longevity; sex reversal; sex 

 difference in activity; and in or out migiration 

 from sampling area by one sex). There is no evi- 

 dence to support any of these explanations in ver- 

 milion snapper, except differential mortality and 

 longevity. Our results show conclusively that rel- 

 ative numbers of females begin to increase (to 

 about 60%) at about 250-300 mm TL, further in- 

 crease to about 70% at 500-550 mm TL, and even- 

 tually reach 90% above 550 mm TL (Table 2). 

 These results indicate that males experience great- 

 er mortalities above 250-300 mm TL, and Grimes 

 (1978) demonstrated greater longevity for females 

 (no male was older than 8 yr, but females reach at 

 least age 10). It is interesting to note that differen- 

 tial mortality commences approximately coinci- 

 den tally with the onset of sexual maturity. 



Our fecundity estimates agree reasonably well 

 with published results for other lutjanids. Starck 



