566 



Fishery Bulletin 103(4) 



Inner shelf 

 Orpheus (n=41) 



10 



10- 



Jiki 



I Hi IIMl I 







Pandora (n=45) 



^L_ 



40 60 80 100 120 40 60 80 100 120 40 60 80 100 120 



Mid-shelf 



10 



o 



Bramble (n=105) 



15r 



: l : I 



Britomart (n=89) 



40 60 80 100 120 40 60 80 100 120 40 60 80 100 120 



Outer shelf 



10 



is 



Pith (n=100) 



hi imB 



10 - 



40 60 80 100 120 







Barnett Patches (n=117) 



, .nill 



40 60 80 100 120 

 Standard length (mm) 



Figure 3 



Size-frequency distributions for Acanthochromis polyacanthus collected 

 from three reefs at each distance stratum from shore. Data were pooled 

 for the three sites sampled at each reef. 



inner-shelf reefs (77 =155), only one fish >100 mm was 

 collected. In contrast, between 38% and 54% offish col- 

 lected from outer-shelf reefs were >100 mm. A mix of 

 inner- and outer-shelf size-frequency distributions was 

 evident for mid-shelf reefs. Bramble and Britomart reefs 

 had 1% and 7% offish >100 mm, respectively, whereas 

 The Slashers had the highest proportion of fish >100 

 mm collected of any reef (67%) including the largest 

 individual fish collected (120 mm); however, this result 

 was more characteristic of outer-shelf reefs. Another 

 conspicuous feature of the cross-shelf size frequencies 

 was the very narrow size range of adult fish collected 

 on inner-shelf reefs in comparison to the size range of 

 fish collected from mid- and outer-shelf locations (Fig. 

 3). Size selectivity due to the collection technique (hand 

 spear) restricted the numbers offish <60 mm that could 

 be collected. 



Maximum age of A. polyacanthus was similar at all 

 reefs sampled (Fig. 4; inner shelf: 9-10 yr, mid-shelf: 

 9-10 yr, outer shelf: 10-11 yr). The largest age class 

 of fish on the inner-and mid-shelf reefs comprised 3-4 

 year olds, whereas on the outer-shelf reefs, 2-year-old 

 fish made up the largest proportion of the populations. 

 The two oldest fish were both collected from outer-shelf 

 reefs (Myrmidon and Barnett Patches) and were both 



11 years old. Strong age-structured cohorts offish were 

 found at some reefs within the same distance stratum 

 and these cohorts were found only at these reefs and 

 distance stratum. For example, there were strong year 

 classes at Pith and Barnett Patches in years 5 and 6 

 that were not found at Myrmidon (Fig. 4). 



Growth 



Variation in patterns of growth was greater among dis- 

 tance strata across the shelf than among reefs within a 

 distance strata (Fig. 5). There was variation in growth 

 between individuals from reefs within each shelf posi- 

 tion and this resulted in variable size-at-age relation- 

 ships (Fig. 5). From inner-shelf reefs, fish from Pandora 

 showed small asymptotic sizes and thus had lower aver- 

 age L x , (L x =77.4 mm) compared to fish from Orpheus 

 and Havannah (L, =87.0, 84.2 mm, respectively; Table 3). 

 Distinct, non-overlapping ellipses formed in 95% confi- 

 dence interval plots of L x in relation to K confirmed that 

 growth curves for fish from Pandora differed from those 

 at Orpheus and Havannah (Fig. 5). Fish collected from 

 mid-shelf reefs (Bramble, Britomart, and The Slashers) 

 showed differences in growth among all reefs (non-over- 

 lapping 95% confidence ellipses; Fig. 5). Growth offish 



