474 



Abstract.— A model was proposed for 

 validation studies of the periodicity 

 and timing of growth checks on fish oto- 

 lith sections, based on measurements 

 of otolith radii around tetracycline 

 (OTC) marks. Continuous variables 

 were obtained by expressing measure- 

 ments of the marginal increment and 

 distance between the OTC mark and 

 the subsequent opaque zone as "frac- 

 tions" of the width of a completed incre- 

 ment cycle within an otolith. The sum of 

 these fractions and the counts of whole 

 cycles completed outside the OTC mark, 

 divided by the known time at liberty, 

 produced estimates of the periodicity of 

 opaque zone completion. Given this rate 

 of completion and known dates of OTC 

 marking and sacrifice, the marginal 

 increment was used to estimate a date 

 on which the outermost opaque zone 

 was completed. The model was applied 

 to 82 marked fish of 1 1 Lutjan us species 

 recovered after 6-22 months at liberty, 

 and an hypothesis of annual periodic- 

 ity, about a mean of 0.96 ±0.32 cycles/yr, 

 was retained for the pooled species 

 along the best, ventral reading axis. 

 Model estimates for L. erythropterus. 

 L. johnii, L. malabaricus, and L. sebae 

 were in the range of 0.78 ±0.22 cycles/yr 

 to 1.03 ±0.29 cycles/yr along this axis. 

 Median ages of these fish were 3+ for L. 

 erythropterus and L. sebac and 5+ for L. 

 johnii. A two-fold difference in somatic 

 and otolith growth detected between 

 field-tagged and captive fish did not 

 affect periodicity. Extension of the model 

 suggested false annuli were induced by 

 changes in salinity or adverse weather 

 On average, annuli were completed 

 within 1-3 months after the minima 

 in water temperature, in the austral 

 spring-early summer, around early 

 September for L. erythropterus and L. 

 johnii, late September for L. nta/ii- 

 baricus and late October for L. sebae. 

 Results from the model were only 

 preliminary for the small samples of 

 L. argentimaculatus, L. bohar, L. car- 

 ponotatus, L. monostigma. L. rivulatus, 

 and L. vitta. although the common 

 validation approach indicated annual 

 periodicity of opaque zone completion 

 for these species. 



A new approach to validation of periodicity 

 and timing of opaque zone formation in the 

 otoliths of eleven species of Lutjanus from 

 the central Great Barrier Reef* 



Mike Cappo 



Australian Institute ol Marine Science, PMB 3 

 Townsville MC, Queensland, Australia 4810 

 E-mail address, m cappo gaims govau 



Peter Eden 



Mote Pty Ltd 



423 Elizabeth Drive 



Vincentia, Jervis Bay, New South Wales, Australia 2540 



Stephen J. Newman 



Western Australian Marine Research Laboratories 



Fisheries Western Australia 



PC Box 20, North Beach, Western Australia 6020 



Simon Robertson 



Central Ageing Facility 



Marine and Freshwater Resources Institute 



Queenscliff. Victoria 3225, Australia 



Manuscript accepted 1 December 1999. 

 Fish. Bull. 98:474-488 (2000). 



There have been recent developments in 

 the use of thin sections of otoliths for 

 counting annual increments in otolith 

 macrostructure as accurate and precise 

 indicators of age for a variety of tropical 

 reef species (see Fowler, 1995 for review). 

 Lifespans of 15-30 years were estimated 

 for tropical snappers in Mexico ( Rocha- 

 Olivares, 1998) and the central Great 

 Barrier Reef (GBR) region (Sheaves, 

 1995: Newman et al, 1996). In contrast, 

 Milton et al. ( 1995 ) applied a radiometric 

 aging technique and estimated longe- 

 vities of <10 years for the "red snap- 

 pers" Lutjanus erythropterus, L. mala- 

 baricus and L. sebae in the Gulf of 

 Carpentaria (Jat. <14°S). These results 

 were one third to one half of the 

 maximum ages estimated by Newman 

 et al. (in press) from sectioned otoliths 

 for the same species in the central GBR 

 (lat. 18-20°S). 



These differences have produced un- 

 certainty about the nature of potential 



development of northern Australian 

 fisheries and raised important questions 

 regarding intraspecific, latitudinal var- 

 iation in otolith interpretation and 

 demographic parameters. There is a 

 clear need to validate age estimates from 

 both regions. 



Francis (1995) proposed that vali- 

 dation is the process of estimating the 

 accuracy of an aging method and that 

 a first stage in the validation involves 

 confirming the temporal meaning of the 

 zones. A three-step conceptual approach 

 to direct age validation studies with 

 tetracycline (OTC) marking and recap- 

 ture has also been used (Fowler, 1990, 

 1995; Fowler and Short, 1998), but 

 no corresponding protocols have been 

 published for the statistical analysis 



Contribution 930 of the Australian Insti- 

 tute of Marine Science, Townsville, Queens- 

 land, Australia. 



