498 



Abstract — We investigated the use 

 of otolith morphology to indicate the 

 stock structure of an exploited ser- 

 ranid coral reef fish, Plectropomua 

 leopardus, on the Great Barrier Reef 

 (GBR), Australia. Otoliths were mea- 

 sured by traditional one- and two- 

 dimensional measures (otolith length, 

 width, area, perimeter, circularity, 

 and rectangularity), as well as by 

 Fourier analysis to capture the finer 

 details of otolith shape. Variables 

 were compared among four regions 

 of the GBR separated by hundreds 

 of kilometers, as well as among three 

 reefs within each region, hundreds of 

 meters to tens of kilometers apart. 

 The temporal stability in otolith 

 structure was examined by compar- 

 ing two cohorts of fully recruited 

 four-year-old P. leopardus collected 

 two years before and two years after 

 a significant disturbance in the 

 southern parts of the GBR caused 

 by a large tropical cyclone in March 

 1997. Results indicated the presence 

 of at least two stocks of P. leopar- 

 dus, although the structure of each 

 stock varied depending on the cohort 

 considered. The results highlight the 

 importance of incorporating data from 

 several years in studies using otolith 

 morphology to discriminate temporary 

 and possibly misleading signals from 

 those that indicate persistent spatial 

 structure in stocks. We conclude that 

 otolith morphology can be used as an 

 initial step to direct further research 

 on groups of P. leopardus that have 

 lived at least a part of their life in 

 different environments. 



The use of otolith morphology to Indicate 

 the stock structure of common coral trout 

 (Plectropomus leopardus) 

 on the Great Barrier Reef, Australia 



Mikaela A. J. Bergenius (contact author)' 



Gavin A. Begg^ 



Bruce D. Mapstone^ 



' CRC (Cooperative Research Centre) Reef Research Centre and 

 School of Marine Biology and Aquaculture 

 James Cook University 

 Townsville, Queensland 4811, Australia 



2 CRC Reef Research Centre 

 James Cook University 



Townsville, Queensland 4811, Australia 



3 Antarctic Climate and Ecosystems CRC 

 Private Bag 80 



Hobart. Tasmania 7001, Australia 

 Email address for M, Bergenius mikaela bergeniusm'icu.edu au 



Manuscript submitted 14 February 2005 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



10 November 2005 by the Scientific Editor. 



Fish. Bull. 104:498-511 11041. 



Marine fish populations are generally 

 distributed over large geographical 

 ranges in a heterogeneous environ- 

 ment. Variable physical and biological 

 processes may restrict the exchange of 

 dispersive larvae and adults between 

 areas within a population's species 

 range, resulting in groups of indi- 

 viduals that are phenotypically or 

 genetically distinguishable. Genetic 

 and environmental processes may 

 also have variable effects on the pro- 

 ductive capacity (e.g.. growth and 

 reproduction) of individuals in dif- 

 ferent areas. Such variations may 

 be directly measurable with variable 

 life history characteristics, but also 

 indirectly measurable with phenotypic 

 characteristics, such as meristic and 

 morphological characteristics. 



Groups of individuals with different 

 genetic or phenotypic characteristics 

 can be defined as separate stocks. 

 Although the precise definition of a 

 stock has been widely debated (see re- 

 views by MacLean and Evans, 1981; 

 Begg, 1998; Booke. 1999), its ultimate 

 meaning should depend on the man- 

 agement objective related to its use. 

 If the management objective is to 

 protect the genetic diversity of a spe- 

 cies, for example, genetic information 

 should be sought. If the purpose is 



to prevent over-fishing and localized 

 depletion, information about life his- 

 tory characteristics is required. This 

 information is needed because groups 

 with different life history characteris- 

 tics may respond differently to fishing 

 pressure and therefore have different 

 vulnerabilities to over-fishing (Cole, 

 1954; Adams. 1980; Jennings et al., 

 1998). 



Variations in morphological charac- 

 teristics of otoliths have proved use- 

 ful for identifying stocks for a range 

 of temperate marine fishes (e.g.. Bird 

 et al., 1986; Castonguay et al., 1991; 

 Smith, 1992; Campana and Cassel- 

 man, 1993; Friedland and Reddin, 

 1994; Begg et al.. 2001; Smith et al., 

 2002), but have not been examined 

 for tropical reef fishes. Differences 

 in morphological characteristics be- 

 tween putative stocks indicate that 

 the stocks have spent some periods of 

 their lives in different environments 

 (Begg et al.. 1999; Cadrin, 2000) and 

 therefore have the potential to develop 

 different life history characteristics. 

 Otolith morphological characteristics 

 used as indicators of stock separa- 

 tion generally fall within one of three 

 categories. The first category includes 

 the traditional one-dimensional linear 

 measurements of size-related attri- 



