Bergenlus et dl Use of otolith morphology to indicate stock structure of Plecliopomus leopardus 



507 



34.3% and 39.7% were correctly classified 

 for cohorts sampled in 1995 and 1999, re- 

 spectively (Table 9). 



Discussion 



Spatial and temporal variation in 

 otolith structure 



Table 5 



Results of ANOVAs comparing otohth principle component (PC) scores 

 of otolith structure from two cohorts of four-year-old Ptectropomus 

 leopardus collected from three reefs in each of four regions in 1995 and 

 1999 on the Great Barrier Reef Only final analyses resulting from 

 pooled terms with F<1 are shown. P-values in bold indicate significant 

 differences (P<0.05). Only PCs with significant differences are shown. 

 MS=mean square. 



This study detected differences in the otolith 

 shape of P. leopardi/s at different spatial 

 and temporal scales across the Great Barrier 

 Reef (GBR), Australia. Although the spa- 

 tial patterns in otolith shape of P. leopardus 

 were not always consistent among different 

 types of shape variables, two main inferences 

 can be made from our results. Firstly, our 

 results indicate that otolith morphology can 

 be useful for identifying groups of individuals 

 of this species that are likely to have spent 

 a significant part of their lives in different 

 environments and therefore may indicate 

 potential stock separation. Overall otolith 

 shape suggested the presence of at least one southern 

 and one northern stock along the GBR. The Storm Cay 

 and Mackay regions consistently belonged to the south- 

 ern stock and the Lizard Island region to the northern 

 stock, and it was inconclusive as to which stock indi- 

 viduals in the Townsville region belonged. It is possible 

 that the main morphological features of otoliths are 

 established in the larval stage and that large amounts 

 of larval dispersal and mixing between areas results 

 in overlap of signatures between stocks. Finer details 

 of otolith shape, however, are most likely influenced by 

 environmental processes during the post larval phase 

 and may therefore provide insights to the separation of 

 stocks during postlarval life. 



Although otolith shape also suggested variation at a 

 smaller, among reef, spatial scale (hundreds to thou- 



Variable Factor 



df 



MS 



PC II 



PC IV 



sands of m) the significant differences in the multi- 

 variate morphological measurement (PC IV) occurred 

 only between two reefs in the Lizard Island region, 

 and therefore it seems unlikely that such small-scale 

 separation is a common phenomenon on the GBR. 

 Nevertheless, the presence of some difference among 

 reefs emphasizes the importance of careful and suffi- 

 cient sampling in order to capture the range of values 

 manifest in small-scale, presumably random, variation 

 within regions and to avoid erroneously ascribing to 

 regional structure what are really a reflection of local- 

 scale variation. Given the hydrodynamic mixing over 

 scales of kilometers, we consider it unlikely that reef- 

 scale variations in morphological variables represent 

 persistent environmentally induced patterns in stock 

 structure. 



