Kritzer: Sex-specific growth and mortality, spawning season, and female maturation of Lut/anus carponotatus 



103 



pan of L. carponotatus can explain the 

 apparently constant mortality rate 

 over many age classes (evidenced by 

 high catch curve r 2 values) given that 

 mortality is often largely a function of 

 body size (Roff, 1992). 



The development and regression of 

 visceral fat stores preceding increases 

 in ovary weight is a pattern that has 

 been observed in other reef fishes, in- 

 cluding tropical surgeonfishes (Acan- 

 thuridae: Fishelson et al., 1985) and 

 groupers (Serranidae: Ferreira, 1995) 

 and temperate rockfishes (Scorpaeni- 

 dae: Guillemot et al., 1985). These pat- 

 terns suggest that the stored lipid is 

 fuelling the energetic costs of spawning. 

 The lack of a similar pattern for males 

 supports the idea that energetic costs 

 associated with production of sperm are 

 low in relation to eggs (Wootton, 1985) 

 thus enabling male L. carponotatus to 

 attain larger sizes, as also reported by 

 Newman et al. (2000). Alternatively, 

 males might spawn more frequently 

 throughout the year than females and 

 the lack of seasonal patterns in lipid 

 storage among males might reflect a 

 more regular energetic demand that 

 precludes energy storage. In any case, 

 these sex-specific growth patterns, 

 coupled with similar mortality rates 

 between the sexes and sex ratios that 

 are at unity or that are at most only 

 slightly female-biased (see below), sug- 

 gest that females are limiting reproduction of 

 this species. Therefore stock dynamics should be 

 modeled in terms of female biology (Hilborn and 

 Walters, 1992). 



The apparently female-biased sex ratio at 

 the Palm Island group starkly contrasts with 

 the heavily male-biased sex ratio reported for 

 mid-shelf reefs of the central GBR by Newman 

 et al. (2000). However, neither a male- nor fe- 

 male-biased sex ratio would be expected from a 

 nonhermaphrodite that is not known to possess a 

 complex mating system such as defense of females 

 or territories. It is possible that the spawning sex 

 ratio (i.e. excluding juveniles) is closer to unity if 

 males mature earlier than females, but this ratio 

 is not possible to assess because male maturation 

 has not yet been examined for this species. The 

 difference between the sex ratio reported in this 

 study and that by Newman et al. (2000) might be 

 due to variation in mating systems across a cross- 

 shelf density gradient (Newman and Williams, 

 1996). Alternatively, the sampling by traps and 

 line fishing conducted by Newman et al. (2000) could be 

 more heavily biased toward males than the sampling by 

 spear fishing used in the present study because of larger 



% 25 



to 



8 2.0 

 1.5 



1.0 

 0.5 

 0.0 



Figure 7 



Monthly mean gonadosomatic index IGSI ±SE; ■) and lipidsomatic index (LSI 

 ±SE; □) values for mature female (A) and all male (Bl Lutjanus carponotatus at 

 the Palm Island group. 



100% 

 80% 

 I" 60% - 



CD 



f 40°= 



20% 



0% 



li 



i 



i 



I 



D Stage II 

  Stage III 

 D Stage IV 



April June Aug Oct Dec Feb 

 Month (1997-98) 



Figure 8 



Monthly frequencies of ovarian stages of mature Lutjanus carpono- 

 tatus at the Palm Island group. Stage descriptions are provided in 

 Table 1. 



size, wider gape, or more aggressive behavior toward bait 

 among males (Cappo and Brown, 1996). Furthermore, it 

 is likely that a female-biased sex ratio as observed at the 



