Bullock et al : Age, growth, and reproduction of Epinephelus itajara 



247 



Discussion 



Age and growth 



The spring-summer period of annulus formation in 

 jewfish seems somewliat protracted. However, there 

 appears to be a considerable range for the duration of 

 annulus deposition in grouper populations: 2 or 3 

 months for Epinephelus morio, E. nigritis, E. drum- 

 mondhayi, and E. niveatus (Moe 1969, Matheson and 

 Huntsman 1984, Moore and Labisky 1984, Manooch 

 and Mason 1987) to 5-7 months for Mycteroperca 

 phenax and M. microlepis (Matheson et al. 1986, Hood 

 and Schlieder 1992). Moe (1969) discussed factors af- 

 fecting annulus formation and concluded that spawn- 

 ing and its associated physiological processes probably 

 caused annulus formation in red grouper. However, an- 

 nulus formation does not always occur in phase with 

 spawning in epinephelines. For example, Matheson et 

 al. (1986) found M. phenax to spawn during April- 

 August in the South Atlantic Bight, but annulus for- 

 mation occurred during December- April. 



The annual deposition of opaque bands, seen in 3- and 

 4-year old OTC-marked jevirfish, needs to be validated 

 for fish older than 10 years. Due to the difficulty in 

 sampling large numbers of these older fish year-round, 

 it is probably not feasible to utilize indirect validation 

 techniques (i.e., marginal increment analysis). Valida- 

 tion will probably require direct observations of in- 

 dividuals that have been injected with OTC and recap- 

 tured after annulus deposition. 



The growth rate of jewfish (i.e., K 0.13/year) falls 

 within or near the range observed for some of its con- 

 geners in the South Atlantic Bight and Gulf of Mex- 

 ico: speckled hind, 0.13/year (Matheson and Himtsman 

 1984) and red grouper, 0.11-0. 18/year (Moe 1969, 

 Muhlia-Melo 1975). However, jewfish growth is some- 

 what faster than that of the deepwater snowy grouper 

 E. niveatus {K 0.07-0.09/year; Matheson and Hunts- 

 man 1984, Moore and Labisky 1984) and considerably 

 greater than that of the second-largest grouper in the 

 western North Atlantic Ocean, the warsaw grouper 

 E. nigritis {K 0.05/year; Manooch and Mason 1987), 

 which may reach weights > 200 kg. 



Reproduction 



We foimd jewfish to be in peak spawning condition dur- 

 ing July- September in the eastern Gulf of Mexico. This 

 agrees with Schroeder's (1924) finding that jewfish 

 spawned during July- August, when heavily exploited 

 aggregations of jewfish appeared off the Florida 

 Keys. Furthermore, Colin (1990) observed what he 

 interpreted as courtship behavior in jewfish off south- 



west Florida during the full moons of August and 

 September. 



When compared with that of females, the slightly 

 smaller size and younger age of males at first matur- 

 ity is unexpected, given that jewfish are assumed to 

 be protogynous hermaphrodites (Smith 1971). Further- 

 more, whereas the youngest fish in our sample was 

 female, as would be expected for a protogynous fish, 

 so was the oldest. However, Sadovy and Shapiro (1987) 

 point out several factors that may obscure differences 

 in length, age, and maturity between males and females 

 of a protogynous fish: (1) Some females may never 

 change sex for lack of genetic or environmental cues 

 and therefore may attain sizes (ages) equal to or greater 

 than males, (2) a fraction of the population may initiate 

 female development but change to males prior to sex- 

 ual maturation, and (3) size at sex-reversal may differ 

 among subpopulations of the same species and thus 

 may obscure differences in length or age distribution 

 between the sexes. Conclusive evidence for proto- 

 gynous hermaphroditism in jewfish (i.e., the presence 

 of transitional individuals) was not found in this study. 

 Transitional individuals in confirmed protogynous 

 hermaphrodites, such as E. morio (Moe 1969) and 

 M. microlepis (Collins et al. 1987, Hood and Schlieder 

 1992), never represent a large percentage of the 

 population; therefore, more extensive collections than 

 ours may be needed to detect the presence of these 

 individuals. 



Fisheries implications 



The life-history characteristics that we describe imply 

 that jewrfish are highly vulnerable to overfishing. Their 

 slow growth, longevity, and presumed low natural mor- 

 tality specify a population composed of cohorts that 

 reach their maximum biomass at relatively old ages 

 (Alverson and Carney 1975). Thus the greatest yield 

 from a cohort of jewfish would be attained at either 

 low rates of fishing or when only large fish are har- 

 vested. If jewfish are indeed protogynous hermaphro- 

 dites, fishing may also disrupt their spawning and 

 recruitment by limiting the number of older males 

 available for spawning (Smith 1982, Bannerot et al. 

 1987, Huntsman and Waters 1987). In addition, be- 

 havioral traits exhibited by large jewfish, such as their 

 general unwariness of spearfishermen and apparent 

 site-specific spawning aggregations (Shroeder 1924, 

 Colin 1990), make them readily available for capture. 

 Fisheries managers of Florida territorial and U.S. Ex- 

 clusive Economic Zone waters have recognized the 

 jewfish's susceptibOity to overfishing and have recently 

 banned all harvest of jewrfish from waters under their 

 jurisdictions. 



