Using otolith chronologies to identify extrinsic drivers of growth of 2 commercially targeted small pelagic fish species

Climate variability is a major cause of changes in marine ecosystems, including changes in both the environment and in many fish species. Understanding the factors influencing key biological characteristics, such as growth, is important for commercially targeted species because these characteristics are used in stock assessments that inform fisheries management. In this study, otoliths were used to examine the growth rates and growth chronologies of 2 commercially targeted small pelagic fish species, the common jack mackerel (Trachurus declivis) and redbait (Emmelichthys nitidus), from 2 regions of southeastern Australia. Both species grew larger off Kangaroo Island (common jack mackerel: asymptotic length [L-infinity]=299.40; redbait: L-infinity=259.79) than off southern New South Wales (common jack mackerel: L-infinity=249.52; redbait: L-infinity=238.89). Temporal growth synchrony in both species and regions (0.17-3.50%) was low compared with that of more site attached benthic species. Interannual variations in growth rates of common jack mackerel off Kangaroo Island were positively correlated with sea-surface temperature (SST), with growth rates 18% higher at 18.0 degrees C than at 16.4 degrees C. However, growth was not correlated with SST or chlorophyll-a concentration for the other species and locations. Developing a more complete understanding of the environmental drivers of growth in these small pelagic fish species may require chronologies to be extended and extrinsic variables in the models to be increased.