Year-class strength and growth rate in young Atlantic cod Gadus morhua

The paradigm relating 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 growth 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-the-year juveniles differed significantly among year-classes. Temperature was a significant, but not necessarily a primary, source of the within-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 times to high larval mortality rates were sufficient to account for much of the 4-fold difference in adult abundance among the year-classes.