146 
Fishery Bulletin 119(2-3) 
in response to regime shifts in the Californian (Rodriguez- 
Sanchez et al., 2002), Humboldt (Alheit and Niquen, 2004), 
Benguela (Cury and Shannon, 2004), and Canary (Sanchez- 
Garrido et al., 2019) current systems. However, changes in 
Chl-a concentration did not affect growth of common jack 
mackerel and redbait in our study, and the observed dif- 
ferences may be the result of other indirect effects that we 
did not measure. The reason for the lack of effect of SST on 
growth of redbait is also unclear. 
Because redbait reside in deeper waters than common 
jack mackerel, the influence of environmental variables, 
such as SST, on their growth may be reduced (Welsford 
and Lyle, 2003; Thresher et al., 2007). This reduction in 
influence of environmental conditions indicates a limita- 
tion of our study: the model is limited to a small number 
of available local variables. In addition, the AIC, weight 
does not provide overwhelming support for one candidate 
model for each species and region, indicating that some 
models are equally supported. Other factors, not included 
in this study, are likely driving the growth of common jack 
mackerel and redbait and can be an avenue for future 
research. Possible model extensions could include an 
upwelling index as a measure of the strength and produc- 
tivity in upwelling events within these regions. Further- 
more, inclusion of an index of EAC strength and extent 
would enable testing whether, and to what magnitude, the 
EAC may be affecting these species in NSW. 
Conclusions 
Here, we reveal inter-regional differences in the growth of 
common jack mackerel and redbait, differences we hypothe- 
size to be linked to the EAC and associated eddies off NSW 
and to upwelling events off KI. The environmental variables 
examined (SST and Chl-a concentration) had little effect on 
growth with the exception of common jack mackerel from KI. 
These populations and the fisheries they support, therefore, 
may be more resilient to some environmental changes than 
has previously been assumed. However, further investigation 
is required to better understand the environmental drivers 
of growth in these populations and to assess the potential 
effects of climate variations over long time periods. Increas- 
ing the sample size is needed to lengthen the time series and 
to increase sample depth. Additional environmental factors, 
such as an upwelling index or intensity and extent of the 
EAC, should be included in future models to improve the 
amount of deviance explained and provide a better under- 
standing of the factors driving growth in these small pelagic 
fishes. Growth chronologies, such as those that we present 
here, are useful for identifying the effects of environmental 
conditions on fish growth and can be incorporated into stock 
assessments to inform the management of fisheries. 
Acknowledgments 
Samples were collected by scientific observers employed by 
the Australian Fisheries Management Authority. A. Ivey 
and N. Navong, from the Aquatic Sciences Research Divi- 
sion of the South Australian Research and Development 
Institute (SARDI Aquatic Sciences), removed, weighed, 
and sectioned otoliths and assisted with aging. Salaries of 
T. Ward and G. Grammer were funded by SARDI Aquatic 
Sciences. 
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