ABSTKACT. The paradigm relat~ng early life history growth rate to survival rate and/or year-class strength has remained largely untested among marine fishes. Using Atlantic cod Gadus morhua on Georges Bank (NW Atlantic) as a test species, I reconstructed the larval and juvenile g]-owth sequences of 5 successive year-classes of cod and related them to 2 independent indices of year-class strength. Larval and juvenile growth sequences reconstructed from the otolith microstructure of young-of-theyear juveniles differed significantly among year-classes. Temperature was a significant, but not necessarily a primary, source of the w~thin-year and between-year variations in growth Neither the larval growth sequence nor the hatch date distribution was correlated with year-class strength. However, otolith size at age and body size at age at the pelagic juvenile stage were both highly correlated with year-class strength. Differences in growth rates and associated exposure t~m e s to high larval mortality rates were sufficient to account for much of the 4-fold difference in adult abundance among the yearclasses.

Radiocarbon (14C) activity in the world's oceans roughly doubled between 1950 and 1970 a s a result of the atmospheric testing of nuclear weapons. Through comparison with the I4C time series reconstructed from nearby corals, Kalish (1993) used the I4C activity of fish otolith cores a s a means of confirming the annulus-based age estimates for those fish. Here I report the first pre-and post-bomb I4C chronology based only on young fish otoliths, thus avoiding all assumptions concerning the age and dale of uptake into the otollth, and any requirement for reference coral chronologies. On the basis of acc,clcrator mass spectrometry (AMS) assays, the I4C activity of 103 young haddock bfelanogrammus aeglcfinus otoliths collected off the eastern coast of Canada increased sharply betwccn 1958 and 1965 and remained elevated theredfter, in phase with published '"C chronologies for bivalves and corals in the North Atlantic. Assays of the '"C content of the extracted otolith core of old haddock served as a dated marker of the year of hatch, thus providing an absolute dge determination for individual fish which was accurate to w~t h l n 1 to 2 yr. Internationally accepted criteria for annulus interpretation in haddock otoliths appear to be accurdte to an a g e of at least 10 yr, a n d to within 2 to 3 yr for haddock up to an a g e of 22 yr.

Trace elements incorporated into the growing surface of the fish otolith (ear stone) reflect the physical and chemical characteristics of the ambient water, although not necessarily in a simplistic manner. Since otoliths grow continuously without resorption throughout the life of the fish, fish population~ growing up in different water masses should produce otoliths of different elemental composition. The otolith elemental composition ('fingerprint') determined with isotope dilution -inductively coupled plasma mass spectroscopy (ID-ICPMS) proved to be an effective discriminator of adjacent population~ of Atlantic cod Gadus morhua off the coast of eastern Canada, with sufficient accuracy as a natural tag to determine population identity in a mixed population fishery. Classification of samples collected from the winter cod fishery on the eastern Scotian Shelf indicated that the annual winter migration out of the Gulf of St. Lawrence is more extensive than was previously believed.

Radiochemical assays of fish otoliths using the radioisotope pair Pb-210/Ra-226 have proven successful in determining the longevity of several long-lived fish species, but are unsuitable for determining ages less than about 3 yr. We tested the utility of the radioisotope pair Th-228/Ra-228 for determining the longevity of the four-winged flyingfish Hirundjchthys affinis of the eastern Caribbean. A new decay equation was developed for interpreting radioactivity in whole otoliths characterized by a nonlinear growth history. Assay results on both whole otoliths and otolith cores indicated that the mean age of adult flyingfish was about 1 yr, and significantly less than 2 yr. The Th-228/Ra-228 radiochemical dating technique appears to be well suited for age determinations of fish up to age 5.

Otolith shape has previously been used to identify ecotypes within the Icelandic cod (Gadus morhua) stock, using DST profiles to validate the results. Fish otolith shape variation has repeatedly been found to be largely determined by growth rate. To examine the effect of growth rate on the relationship between otolith shape and cod ecotypes (using the Pan I genotype as a proxy for ecotype), 826 archived sagittal otoliths collected over a 52 year sampling period were retrieved, the individual growth rate calculated, and otolith shape described using both Normalized Elliptic Fourier transform and Discrete Wavelet transform. Discriminant functions of otolith shape yielded high ecotype classification success, whether using Fourier or Wavelet descriptors, but only when excluding a heterozygous genotype from the analysis. The otolith shape variability of this genotype lowered the classification success, while otolith shape, in turn, was significantly affected by growth rate and cohort. Growth rate differences previously reported for the ecotypes were present, but were less marked than expected and indeed, growth rate variance attributable to ecotype identity was dwarfed by cohort- and location-related variance in growth. Such a strong effect of growth rate suggests that cod ecotype discrimination based on otolith shape is sensitive to both temporal and spatial variations in growth, which can mask the effect of ecotype-related growth rate differences on otolith shape.