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Fishery Bulletin 92(4). 1994 



as 1967 (Fisheries Agency of Japan, 1967), prelimi- 

 nary studies suggested that the quantitative analy- 

 sis of the microconstituents and trace elements in 

 otoliths, vertebrae, and scales could provide infor- 

 mation on population structure and the movements 

 of individual fish. This suggestion was based on two 

 assumptions and a hypothesis. The assumptions 

 were that 1) the calcified structures are not suscep- 

 tible to dissolution or resorption and 2) the growth 

 of these tissues continues throughout life. If these 

 assumptions are correct, calcified structures are per- 

 manent records of the influence of endogenous and 

 exogenous factors on their calcium-protein matrices. 

 The hypothesis is that differences in the environ- 

 ments to which fish in each population are exposed 

 affect the incorporation of elements in calcified struc- 

 tures, which results in chemical compositions spe- 

 cific to each population. An extensive fisheries lit- 

 erature supports the assumptions for otoliths, if not 

 perhaps for scales and vertebrae (e.g. Sauer and 

 Watabe, 1989). The working hypothesis also appears 

 reasonable, given an extensive literature on inver- 

 tebrates that relates differences in the composition 

 of, for example, mollusc shells, and coral skeletons 

 to a range of environmental and physiological condi- 

 tions (Thompson and Livingston, 1970; Weber, 1973; 

 Houck et al., 1977; Buchardt and Fritz, 1978; Smith et 

 al., 1979; Rosenberg, 1980; Schneider and Smith, 1982). 



Since 1967, several studies have investigated 

 whether the composition of calcified structures indi- 

 cates stock or subpopulation identity in fishes (e.g. 

 Klokov and Frolenko, 1970; Calaprice, 1971, 1985; 

 Calaprice et al., 1971, 1975; Bagenal et al., 1973; 

 Gauldie and Nathan, 1977; Behrens Yamada et al., 

 1987; Lapi and Mulligan, 1981; Mulligan et al., 1983, 

 1987; Edmonds et al., 1989; Calaprice 1 ), using a va- 

 riety of analytical techniques (see reviews by 

 Coutant, 1990; Gunn et al., 1992). The results have 

 been mixed. In part, this is because most techniques 

 used required a relatively large amount of material 

 for analysis. Otoliths or bones from many individu- 

 als often had to be pooled to reach the minimum 

 sample mass required. Because individual and onto- 

 genetic variability could not be addressed, it has been 

 difficult to assess the potential of the approach. 



In 1987, we began experiments with a view to us- 

 ing fine-scale, ontogenetic variation in the composi- 

 tion offish otoliths as an indicator of movement and 

 migration patterns. The results of the first step — 

 an investigation of the operating characteristics of 

 probe microanalyzers as they affect data quality and 

 the development of reliable techniques for 'life his- 



1 Calaprice, J. R. 1983. X-ray fluorescence study of stock varia- 

 tion in bluefin tuna. Status report submitted to NMFS, Miami, 

 March 1983, 60 p. 



tory scans' across otoliths — are reported in Gunn et 

 al. (1992) and Sie and Thresher (1992). In this pa- 

 per, we evaluate the extent to which otolith composi- 

 tion in a test species varies ontogenetically, among 

 individuals within sites, and among sites, in order 

 to assess whether such variation is of sufficient mag- 

 nitude for, and contributes to, resolving population 

 structure in the species. 



The species chosen for study was the jackass 

 morwong, Nemadactylus macropterus (Cheilo- 

 dactylidae), a moderate-sized (maximum about 70 

 cm standard length), bottom-dwelling fish common 

 on the middle and outer continental shelf off south- 

 ern Australia, New Zealand, South Africa, and the 

 Pacific coast of South America (Robertson, 1978). The 

 species was chosen for two reasons. First, the popu- 

 lation structure of the species in Australian waters 

 is contentious. On the one hand, regional declines in 

 catch rates suggest localized stocks, which is consis- 

 tent with work in New Zealand, where the species 

 has three geographically discrete populations 

 (Gauldie and Nathan, 1977; Robertson, 1978) . On 

 the other hand, a small amount of tagging data for 

 adults (Smith, 1989), allozyme data for specimens 

 collected in southeast Australia (Richardson, 1982), 

 and recent allozyme and mitochondrial DNA analy- 

 ses for the entire Australian range (Elliott and Ward, 

 1994; Grewe et al., in press) suggest a single, broadly 

 distributed population (Smith, 1989; Tilzey et al., 

 1990). This interpretation also appears to be consis- 

 tent with the early life history of the species: N. 

 macropterus spawns along the middle continental 

 shelf, has a planktonic duration of 9-12 months, and 

 has a morphologically specialized late-stage larva 

 ('paper fish') that is neustonic and generally caught 

 offshore of the continental shelf (Vooren, 1972). This 

 combination is taken to imply high rates of local mix- 

 ing during the larval stage. 



Nemadactylus macropterus was also chosen be- 

 cause of uncertainty about the location of its nurs- 

 ery areas in Australia. To date, the only place in Aus- 

 tralia where large numbers of juveniles have been 

 found is the shallow bays and inlets of southeastern 

 Tasmania. As a result, it has been suggested that 

 this area is a critical habitat supporting the entire 

 Australian population (Tilzey et al., 1990). Given 

 continuing coastal development in this area, if the 

 hypothesis is correct, conservation measures need to 

 be developed and implemented to ensure the contin- 

 ued viability of the fishery. 



Analysis of otolith composition could help resolve 

 both questions. With regard to population structure, 

 we hypothesized that if there are discrete spawning 

 populations in Australian waters, then the composi- 

 tion of the central, first-forming portion of the otolith 



