Bergenius et al Use of otolith morphology to indicate stock structure of Pleclropomus leopardus 



499 



butes, such as otolith length and width (e.g., Begg and 

 Brown, 2000; Bolles and Begg, 2000) and distances 

 between specific features on the otolith (e.g., Turan, 

 2000). Internal otolith measurements, such as nucleus 

 length (e.g., Messeih, 1972; Neilson et al., 1985) and 

 width of hyaline bands or increments (e.g., Begg et al., 

 2001) also fall within this category. The second cat- 

 egory comprises two-dimensional size measurements, 

 such as area, perimeter (e.g., Campana and Casselman, 

 1993; Begg and Brown, 2000; Bolles and Begg, 2000) 

 and different shape indices, including circularity and 

 rectangularity (e.g.. Friedland and Reddin, 1994; Begg 

 and Brown, 2000; Bolles and Begg 2000. Tuset et al., 

 2003). A third, more recent morphological technique 

 examines the two-dimensional outline of otolith shape 

 using Fourier analysis (e.g.. Bird et al., 1986; Smith, 

 1992; Campana and Casselman, 1993; Begg and Brown, 

 2000; Smith et al., 2002). Fourier analysis produces a 

 series of cosine and sine curves from the coordinates of 

 a traced outline which, when added together, describe 

 the outline of the traced form. The cosine and sine 

 curves can be defined mathematically in a series of 

 Fourier descriptors and used as variables to compare 

 otolith shapes among individuals or potential stocks 

 (Christopher and Waters, 1974; Younker and Ehrlich, 

 1977). 



Plectropomus leopardus (common coral trout) (also 

 known as leopard coralgrouper, FishBaseM is the most 

 important commercially and recreationally harvested 

 reef fish on the Great Barrier Reef (GBR), Australia 

 (Mapstone et al.'-; Williams''). Plectropomus leopardus 

 comprises between 35% and 50% of the commercial reef 

 line catch annually (Mapstone et al.-) and in 2004 a 

 total allowable commercial catch (TACC) of 1300 t was 

 implemented. Regional (hundreds of km) or inter-reef 

 (hundreds to thousands of m) variations have been 

 demonstrated in some life history characteristics of P. 

 leopardus on the GBR (Begg et al., 2005), such as differ- 

 ences in density (Ayling et al.^), reproductive strategies 

 (Adams, 2002), size and age (Russ et al., 1995; Lou et 

 al., 2005), and mortality (Russ et al., 1995, 1998; Map- 



' FishBase. http://www.fishbase.org/search.php [accessed June 

 2006]. 



2 Mapstone, B. D, J. P. MacKinley, and C. R. Davies. 1996. A 

 description of the commercial reef line fishery log book data 

 held by the Queensland Fisheries Management Authority, 

 480 p. Department of Primary Industries, Queensland, 

 Brisbane. (Available from the Department of Primary Indus- 

 tries and Fisheries, GPO Box 46, Brisbane, Queensland 

 4001, Australia.] 



^ Williams, L. E. 2002. Queensland's fisheries resources. 

 Current condition and trends 1988-2000, 180 p. Department 

 of Primary Industries, Queensland, Brisbane. (Available 

 from the Department of Primary Industries and Fisheries, 

 GPO Box 46, Brisbane, Queensland 4001, Australia.] 



"Ayling, A., M. A. Samoilys, and R. Dan. 2000. Trends 

 in common coral trout populations on the Great Barrier 

 Reef, 36 p. Information Series QI00063. Department of 

 Primary Industries, Queensland, Brisbane. (Available from 

 the Department of Primary Industries and Fisheries, GPO 

 Box 46, Brisbane, Queensland 4001, Australia.] 



stone et al., 2004). Current management arrangements 

 (such as TACC, fish size limits, gear restrictions, recre- 

 ational bag limits, and spatial and temporal closures), 

 however, do not incorporate the localized or regional 

 spatial structure in the life history characteristics of P. 

 leopardus or any other exploited species on the GBR. 



The overall aim of this study therefore was to ex- 

 amine the use of otolith morphology for determining 

 the stock structure of P. leopardus on the GBR. We 

 investigated the broad spatial scale of P. leopardus by 

 comparing aspects of otolith morphology among fish 

 collected from four regions of the GBR, separated by 

 hundreds of kilometers (north to south). Otolith struc- 

 ture was also assessed at finer spatial scales, among 

 P. leopardus collected from neighboring reefs separated 

 by hundreds of meters to tens of kilometers, within 

 each of the four regions. In addition, because temporal 

 variation in otolith shape could confound the spatial 

 information if samples were taken from only one time, 

 we also compared otolith morphological characteristics 

 from two cohorts of P. leopardus with non-overlapping 

 life histories either side of a significant environmen- 

 tal disturbance that affected the southern half of the 

 GBR (the large and persistent Cyclone Justin in IVIarch 

 1997). Spatially variable effects of the Cyclone, such as 

 a significant drop in temperature and salinity in large 

 parts of the GBR (AIMS'), provided us with a unique 

 opportunity to test the temporal stability of spatial pat- 

 terns in otolith morphology. 



Methods and data analysis 



Background 



Common coral trout ^Plectropomus leopardus) were col- 

 lected as part of the Cooperative Research Centre for 

 the Great Barrier Reef World Heritage Area (CRC Reef) 

 Effects of Line Fishing (ELF) experiment (Campbell et 

 al., 2001; Mapstone et al., 2004). The ELF experiment, 

 which began in 1995 and concluded in 2006, monitored 

 line-caught fish populations from a group of six neigh- 

 boring reefs in each of four regions extending over 7° of 

 latitude along the GBR (Fig. 1; Mapstone et al.'\ 1996, 

 1997, 2004; Davies et al.M. At the start of the experi- 



' AIMS (Australian Institute of Marine Science). 2005. Un- 

 publ. data. (Available from http://www.aims.gov.au/pages/ 

 facilities/weather-stations/aws-ytd.html) (Accessed on 1 

 February 2005]. 



« Mapstone, B. D.. C. R. Davies, D. C. Lou, A. E. Punt, G. R. Russ, 

 D.A.J. Ryan, A. D. M. Smith, and M. Williams. 1998. Ef- 

 fects of line fishing experiment 1995-1997: progress report, 

 86 p. (Available from the CRC Reef Research Centre, PO 

 Box 772, Townsville, Queensland 4810, Australia.] 



" Davies, C. R., B. D. Mapstone, A. Ayling, D. C. Lou, A. 

 E. Punt, G. R. Russ, M. A. Samoilys, A. D. M. Smith, D. 

 J. Welch, and M. Williams. 1998. Effects of line fishing 

 experiment 1995-1997: project structure and operations, 

 28 p. [Available from the CRC Reef Research Centre, PO 

 Box 772, Townsville, Queensland 4810, Australia.] 



