104 



Fishery Bulletin 102(1) 



Sep Oct Nov Dec Jan 

 Month (1997-98) 



Feb 



Mar 



Figure 10 



Mean gonadosomatic index (GSI ±SE) for mature female 

 Lutjanus carponotatus at the Palm Island group during the 

 September through March spawning season for small (<230 mm 

 fork length; ■> and large (<230 mm fork length; □) size classes. 

 The percentage of fish at stage IV (see Table 1) is indicated above 

 each data point. 



Palm Island group is not a prevalent feature 

 of L. carponotatus populations. Rather, the 

 strong statistical suggestion of a sex ratio 

 quite different from unity might be due to 

 the fact that sex ratios often show temporal 

 variability (e.g. Stergiou et al., 1996) coupled 

 with the propensity to achieve statistically 

 significant differences when using large 

 sample sizes (Johnson, 1999). 



Maturation schedules and sex-specific 

 growth differences were consistent between 

 the island groups, but overall growth pat- 

 terns differed, with Lizard Island group fish 

 reaching larger asymptotic body sizes. Given 

 the vast distance between the island groups, 

 these differences might be due to inherent 

 genetic differences between the populations. 

 Or, effects of temperature (the Palm Island 

 group sits at a higher latitude), turbidity, 

 freshwater run-off (the Palm Island group 

 sits closer to a river mouth and has more 

 developed mangrove systems), or other 

 environmental factors could be driving the 

 differences. Of course, these possibilities are 

 not mutually exclusive. 



The larger ovaries observed among Liz- 

 ard Island females might be due to further 

 spatial differences or might be an effect of 

 timing of sampling. The temporal resolution 

 of sampling aimed to identify the extent of 

 the spawning season but was too coarse to 

 account for intramonth differences in ovar- 

 ian development. Large changes in ovary 

 size might occur within stage IV, and the 

 final progression to immediate prespawning 

 stages can be rapid (e.g. Davis and West, 

 1993). The Lizard Island group sample was collected 

 from 17 to 23 October 1998, whereas the corresponding 

 Palm Island group sample was collected from 11 to 12 

 October 1998. The October 1998 new moon was on the 

 20 th , and P. leopardus, the only GBR species for which 

 lunar spawning patterns have been reported, spawns 

 primarily around the new moon (Samoilys, 1997). If 

 L. carponotatus spawning is also centered around the 

 new moon, the spatial differences in ovary weight at 

 body weight might be due to more advanced develop- 

 ment toward full hydration within the Lizard Island 

 group sample. In fact, the higher proportion of stage-FV 

 ovaries within the October Lizard Island group sample 

 (96%) compared with the October Palm Island group 

 sample (78'i ), coupled with the higher relative ovary 

 weights at the Lizard Island group in October, can be 

 taken as preliminary evidence that L. carponotatus 

 spawns at the new moon. 



Comparison with other reef fishes 



The growth differences between male and female L. 

 carponotatus contrast with a general trend of larger 

 body sizes among female lutjanids observed in Atlan- 



