ACCURACY OF AGE ESTIMATES FOR LARVAL SEBASTES JORDANI

We examine some issues concerning the accuracy of larval age estimates for Sebastes jordani. To localize a starting point for daily incremen t counts, gestating and planktonic larvae were examined to determine w hether an extrusion check forms at parturition. We also assessed 1) th e resolution limitations of optical microscopy in ageing larvae, 2) th e precision of age estimates, and 3) the effect of specimen age on the reliability of ages. Preextrusion increments are commonly observed in gestating and planktonic larvae, but a distinctive extrusion check fo rms in the otolith at parturition. This feature occurs predictably at a radius of 15-19 mu m and provides an unambiguous starting point for increment counts. Observations of larval otoliths with a scanning elec tron microscope revealed that the minimum size of postextrusion increm ents is similar to 0.6 mu m, which is large enough to be resolved with a high-quality optical system. Cross-checking of ages among three rea ders showed 84% agreement to within +/-1 d and no systematic differenc es among readers. The clarity of otolith microstructure resulted in hi gh confidence scores for age estimates; however, very young larvae (0- 3 d) were the most difficult to age. An exponential growth model fitte d to 2,203 aged larvae indicated that during the first month of life, growth in length proceeds at the rate of 2.75%. d(-1).