ESTIMATING SOME EARLY LIFE HISTORY PARAMETERS IN 



A TROPICAL CLUPEID, HERKLOTSICHTHYS CASTELNAUI, FROM 



DAILY GROWTH INCREMENTS IN OTOLITHS' 



Simon R. Thorrold^ 



ABSTRACT 



Growth increments in otoliths were used to estimate the age of larval Herklotsichthys castehmui, a tropical 

 clupeid. collected from Townsville, northeastern Australia, in spring/summer of 1987. Daily periodicity 

 of increment formation was confirmed by treating larvae with tetracycline and examining otoliths after 

 a known time period. Initial increments were assumed to form at hatching; ages were thus minimum 

 estimates. 



Laird-Gompertz and von Bertalanffy growth models fitted the resultant length-at-age data equally 

 well; therefore, only the Laird-Gompertz model is presented. Specific growth rates declined from 7.4% 

 of standard length per day at 4-5 days old to 0.4% of standard length per day at metamorphosis, 45-50 

 days after hatching. Absolute growth rates also declined, from 0.6 mm per day at 4-5 days to 0.08 mm 

 per day at 44-45 days. Initial absolute growth rates are as high as any reported for clupeid larvae in 

 the field; after this initial burst, however, the growth trajectory appeared similar to those reported for 

 herring and pilchard larvae in temperate waters. 



Spawning periodicity ofH. castelnaui during the sampling period was determined by e,xamining tem- 

 poral distribution of birthdates from otolith-aged larvae. There was indication of semilunar peaks in spawn- 

 ing activity, apparently associated with quarter moon phases. 



A central problem in fisheries research is under- 

 standing mechanisms determining year-class 

 strength. Evidence suggests that regulation of year 

 classes occurs during the early life history of most 

 fish species (Parrish 1973; Smith 1985), and at- 

 tempts to account for recruitment variability have 

 focussed on this period of the life cycle (e.g., Hjort 

 1914; Gushing 1975; Koslow et al. 1987). Growth has 

 been established as a critical parameter in the sur- 

 vival and subsequent recruitment of larval marine 

 fishes (Houde 1987). Weight gains of orders of mag- 

 nitude during larval life suggest a potential for ex- 

 tremely variable growth trajectories which may be 

 reflected in a concomitant variability in survivorship. 

 Growth rates are intrinsically related to suscepti- 

 bility to both starvation (Lasker 1981) and predation 

 (Rothschild and Rooth 1982). Small changes in 

 growth rate can also have a dramatic effect on 

 recruitment by determining stage durations over 

 which high mortality indices may operate (Houde 

 1987). 

 Length-frequency methods have been used exten- 



'Contribution No. 447 from the Australian Institute of Marine 

 Science, Queensland, Australia. 



^Australian Institute of Marine Science, P M B No. 3 Towns- 

 ville M.S.O., Queensland 4810, Australia. 



Manuscript accepted October 1988. 

 Fishery Bulletin, U.S. 87:73-83- 



sively to estimate growth in larval fishes, but growth 

 curves generated by this technique may be biased 

 by age- and cohort-specific changes in growth rates 

 (Crecco et al. 1983). Protracted spawning seasons 

 may further complicate growth estimates because 

 of the difficulties associated with connecting length 

 modes in polymodal length-frequency distributions 

 (Lough et al. 1982). Modal progression can also only 

 provide mean growth estimates for larval popula- 

 tions. These estimates are often averaged over 

 months or years, whereas the relevant temporal 

 scale for critical life history events may be hours or 

 days (Fortier and Leggett 1985). 



The accuracy and precision of growth estimates 

 for larval fishes have been greatly enhanced by the 

 discovery of daily incremental rings in the otoliths 

 of some fishes (Pannella 1971; see Campana and 

 Neilson 1985; Jones 1986 for recent reviews). Age- 

 ing by counting otolith growth increments allows 

 a direct measure of length-at-age for calculation of 

 growth curves and may provide information on in- 

 dividual age and growth rates. Growth estimates 

 have been obtained from a variety of species in this 

 manner (e.g., Struthsaker and Uchiyama 1976; 

 Methot and Kramer 1979). Back-calculation of daily 

 rings may reveal temporal distribution of birthdates 

 (Townsend and Graham 1981; Methot 1983), and 



73 



