Abstract. — Comparisons are 

 made between estimates of ages and 

 growth of the flathead Platycephalus 

 speculator Klunzinger, from a tem- 

 perate Western Austrahan estuary, 

 using data obtained from whole and 

 sectioned otoliths. The consistent an- 

 nual trends shown by the width of 

 the opaque zone on the periphery 

 (marginal increment) of sectioned 

 otoliths, irrespective of the number 

 of translucent zones, demonstrate 

 that the translucent zones in these 

 otoliths correspond to annuli. While 

 the marginal increments on whole 

 otoliths also showed a similar marked 

 and consistent annual trend when a 

 single translucent zone was present, 

 they were far less conspicuous when 

 two or more translucent zones were 

 observed. The large sample size and 

 strong trends shown by marginal in- 

 crements on otoliths exhibiting one 

 translucent zone accounts for the 

 fact that, when data for all whole 

 otoliths are pooled, the marginal in- 

 crement still shows a consistent an- 

 nual trend. Sectioning of otoliths 

 enhances the ability to differentiate 

 between the outer opaque and trans- 

 lucent zones, and also often reveals 

 one or more additional inner translu- 

 cent zones in older fish. The use of 

 whole otoliths frequently underesti- 

 mated age by one year in 2 -t- to 4 -i- 

 fish and two years in 5 -i- to 10 -i- fish, 

 and by as much as five or six years 

 in the oldest fish (1 1 -t- and 12 -i- ). The 

 respective 95% confidence limits for 

 the parameters La>, K, and tp in 

 the von Bertalanffy growth equa- 

 tions for males, calculated using data 

 from sectioned otoliths, overlapped 

 those calculated from data for whole 

 otoliths, and the same was true for 

 K with females. This similarity in 

 growth curves in particularly the 

 first four years of life can be attrib- 

 uted to the fact that approximately 

 74 and 65% of the growth of males 

 and females, respectively, occurred 

 in the first three years, when under- 

 estimates of age were limited. 



Influence of sectioning otoliths 

 on marginal Increment trends 

 and age and growth estimates for 

 the flathead Platycephalus speculator 



Glenn A. Hyndes 



School of Biological and Environmental Sciences, Murdoch University 

 Murdoch, Western Australia 6150, Australia 



Neil R. Loneragan 



School of Biological and Environmental Sciences, Murdoch University 

 Murdoch, Western Australia 6150, Australia 

 Present address: CSIRO Division of Fisheries 

 P.O. Box 120, Cleveland, Queensland 4163, Australia 



Ian C. Potter 



School of Biological and Environmental Sciences, Murdoch University 

 Murdoch, Western Australia 6150, Australia 



Manuscript accepted 18 February 1992. 

 Fishery Bulletin, U.S. 90:276-284 (1992). 



Since assessments of fish stocks often 

 rely on information on age composi- 

 tion, it is crucial that any age esti- 

 mates used for such assessments are 

 validated (Beamish and McFarlane 

 1983, Casselman 1987). Validation 

 that growth zones on hard structures, 

 such as otoliths, scales, and spines, 

 are formed annually is often implied 

 by establishing that the pattern of 

 growth on the periphery of these 

 structures follows a consistent an- 

 nual trend (e.g., Johnson 1983, Ma- 

 ceina et al. 1987, Potter et al. 1988, 

 Beckman et al. 1989). In otoliths of 

 fish in temperate waters, an opaque 

 zone generally starts to form in the 

 spring immediately outside the trans- 

 lucent zone laid down during the 

 preceding winter. The width of this 

 opaque zone usually increases be- 

 tween spring and autumn. Although 

 a subsequent retardation of growth 

 during winter results in formation of 

 the translucent zone at the edge of 

 the otolith, this translucent zone fre- 

 quently cannot be readily detected 

 until the following spring, when it 

 becomes delineated by the formation 

 of a new opaque zone. The distance 

 outside the outer translucent zone 



constitutes the marginal increment. 

 Therefore, if the outer opaque and 

 translucent zones are formed annu- 

 ally, the marginal increment should 

 decline only once during the year. 

 Verification that trends shown by the 

 marginal increments follow a pattern 

 consistent with annual growth is an 

 important method for establishing 

 that the alternating translucent and 

 opaque zones each correspond to an- 

 nuli and are thus appropriate for use 

 in ageing (Brothers 1983). 



Many workers have presented data 

 which showed that an annual trend 

 was followed either by the marginal 

 increment, when data for all otoliths 

 in each sample were pooled, or by 

 the overall incidence of otoliths pos- 

 sessing either translucent or opaque 

 zones on their outer edge. When 

 these have shown a consistent annual 

 trend, it has often been concluded 

 that all translucent zones correspond 

 to annuli (e.g., Nel et al. 1985, Reis 

 1986, Rincon and Lobon-Cervia 1989, 

 Crozier 1990, Hayse 1990). However, 

 trends shown in such pooled data will 

 be strongly influenced by those of the 

 dominant groups, vis a vis the num- 

 ber of translucent zones, and may 



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