Journal zyxwvuts of zyxwvuts Fish Biology zyxwvut (1992) zyxwvu 41,749-763 Patterns of increment width and strontium zyx : calcium ratios in otoliths of juvenile rock blackfish, Givella elevata (M.) N. K. GALLAHAR AND M. J. KINGSFORD School of Biological Sciences, Zoology A08, University of Sydney, N.S. W. 2006, Australia (Received I November 1991, Accepted21 March 1992) Otoliths of juvenile Girellu elevufu (M.) were examined to obtain information about the environmental conditions experienced during early life. Patterns of increment deposition and elemental ratios in otoliths were compared in wild fish. A tetracycline experiment indicated that increments were deposited daily in juveniles. Although different patterns in the spacing of increments were found among juveniles collected at different locations and times, the widest increments were always found in the first zyxwv 40 increments. Strontium : calcium (Sr : Ca) ratios increased with age in the otoliths of most wild G. elevata. The patterns of increment width and Sr : Ca ratios were not related and, therefore, were probably not under the same relative control by environmental or physiological factors. Although the number of increments can be used to age juvenile G. elevatu, the utility ofincrement widths and Sr : Ca ratios as environmental predictors in this species is questionable without experimental validation. Key words: otolith; increment width; Sr/Ca ratio I. INTRODUCTION A knowledge of the environmental conditions experienced by reef fish during early life would improve our understanding of processes affecting survivorship and dispersal of young. Most species of reef fish release eggs or larvae into the pelagic environment (Johannes, 1978; Kingsford, 1988) where young may experience variation in temperature and food supply due to different water masses before settling back to the reef as juveniles. Larvae may be exposed to different environmental regimes for extended periods ( > 10 days) when they encounter water masses like the East Australia Current (Mulhearn, 1987). Some studies suggest that a record of changes in environmental conditions may be stored in the otoliths of young fish, in the form of changes in daily increment width (Neilson & Geen, 1982) and changes in elemental ratios, such as strontium : calcium (Sr : Ca) (Radtke, 1984) and iron : calcium (Fe : Ca) (Gauldie et al., 1980). The use of otoliths to age larvae and juveniles, with validation of the periodicity of increment deposition, is a widely accepted and useful technique (Campana & Neilson. 1985). Variation in the widths of these daily increments has further been related to growth, food availability and water temperature (Neilson & Geen, 1982; Victor, 1982; Wilson & Larkin, 1982). Secor & Dean (1989) caution, however, that one cannot assume that increment width and somatic growth are linearly related, and that the actual relationship may be more complicated (see Mosegaard et al., 1988;Wright et al., 1990). It has also been shown that increment growth of otoliths can occur after cessation of fish growth (Campana, 1984). Otolith microchemistry has the potential to provide a record of the environmental conditions experienced by a fish during early life. Strontium is 749 0022-1 I12,92/011749+ zyxwvuts 15 %08.00/0 0 1992 The Fisheries Society of the British Isles