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can be constructed by examining otoliths, metabolically 
inert calcified structures that provide information about 
biological events and environmental conditions through- 
out a fish’s life (Campana, 1999). The width of an otolith 
increment can be linked to the somatic growth rate of a 
fish (Ashworth et al., 2017). Ambient factors (e.g., tem- 
perature and food availability) influence the physiology 
and somatic growth rates of fishes. The width of growth 
increments (pairs of opaque and translucent bands) fluc- 
tuates in response to variations in growth rates (Morales- 
Nin, 2000; Kerr and Campana, 2014). Age and growth 
models have been developed to produce growth increment 
chronologies that can be used to investigate abiotic and 
biotic factors influencing growth (Black et al., 2005; Mor- 
rongiello and Thresher, 2015). 
Growth chronologies have been applied to a range of fish 
species, including the black bream (Acanthopagrus butch- 
ert) (Doubleday et al., 2015), the sand whiting (Sillago 
ciliata) (Stocks et al., 2011), species of ocean perch (Heli- 
colenus spp.) (Grammer et al., 2017), the Atlantic horse 
mackerel (Tanner et al., 2019), the Atlantic herring (Clu- 
pea harengus) (Smoliriski, 2019), and the snapper (Chrys- 
ophrys auratus) (Martino et al., 2019), to investigate the 
effects of climatic events, climate change, and environmen- 
tal conditions on fish growth (Izzo et al., 2016; Mazloumi 
et al., 2017; Barrow et al., 2018). However, most studies 
in which this method was used have focused on benthic 
and estuarine species that tend to be more site-attached, 
with few growth chronology studies done on highly mobile, 
pelagic fishes (Smoliriski, 2019). 
In Australia, mid-water trawl and purse-seine nets are 
used in the Commonwealth small pelagic fishery 6—370 km 
(3-200 nmi) offshore between southwestern Western Aus- 
tralia and southern Queensland (Ward and Grammer’). The 
fishery targets spotted chub mackerel (Scomber austral- 
asicus); common jack mackerel (Trachurus declivis), also 
known as greenback horse mackerel; redbait (Emmelichthys 
nitidus); and Pacific sardine (Sardinops sagax) (Ward 
and Grammer’). The catch of the small pelagic fishery in 
2018-2019 has been estimated at around 10,000 metric 
tons, which is approximately 5% of the annual fishery pro- 
duction in Australia (Steven et al.”). The harvest strategy 
for the fishery includes the use of fishery-independent sur- 
veys that follow the daily egg production method for each 
species, along with catch and effort data, to determine total 
allowable catch limits (AFMA?®). 
! Ward, T. M., and G. L. Grammer. 2018. Commonwealth small 
pelagic fishery: fishery assessment report 2017. Report to the 
Australian Fisheries Management Authority. South Aust. Res. 
Dev. Inst., SARDI Publ. F2010/000270-9, SARDI Res. Rep. Ser. 
982, 114 p. SARDI Aquat. Sci., Adelaide, Australia. [Available 
from website.] 
? Steven, A. H., D. Mobsby, and R. Curtotti. 2020. Australian fish- 
eries and aquaculture statistics 2018, 135 p. Fish. Res. Dev. Corp. 
Project 2019-093. Aust. Bur. Agric. Resour. Econ. Sci., Canberra, 
Australia. [Available from website.] 
3 AFMA (Australian Fisheries Management Authority). 2019. 
Annual report 2018-19, 169 p. Aust. Fish. Manage. Auth., 
Canberra, Australia. [Available from website.] 
The common jack mackerel is a schooling pelagic species 
distributed across the temperate coastal waters of south- 
ern and southeastern Australia, ranging from Queensland 
to Western Australia (Gomon et al., 2008). The species is 
most commonly found over the continental shelf and outer 
shelf margin in depths of 20-300 m, but it can be found to 
depths of 500 m (Pullen and TDPIF, 1994). In Australia, 
the existence of 2 populations of common jack mackerel 
has been suggested (Ward and Grammer’); however, the 
movement patterns of common jack mackerel have been 
examined in no studies. The redbait is a schooling pelagic 
species occurring worldwide in tropical and temperate 
waters over continental shelfs and in association with 
seamounts, mid-ocean ridges, and islands (Welsford and 
Lyle, 2003). This species is commonly found in depths of 
100—400 m but can be found to depths of 800 m (Welsford 
and Lyle, 2003). In no studies have the movements or stock 
structure of redbait in Australia been assessed (Ward and 
Grammer’). Long-term trends of abundance of common 
jack mackerel have changed over time with a shift in the 
dominant small pelagic species from common jack mack- 
erel to redbait in the 1990s (McLeod et al., 2012). It has 
been suggested that this shift in abundance may be driven 
by environmental change in the region (McLeod et al., 
2012), raising questions over how these changes may 
affect other aspects of their population dynamics, such as 
their growth. 
Different oceanographic features are likely to influ- 
ence the growth of small pelagic fish across their range 
off Australia. Along the southeastern coast of Australia, 
the Pacific Ocean is influenced by the El Nino—Southern 
Oscillation and Interdecadal Pacific Oscillation, phenom- 
ena that result in changes in rainfall, SST, and trade wind 
strength (Fiedler, 2002; Overland et al., 2010). In addition, 
the East Australian Current (EAC) is a key oceanographic 
feature that moves warm, nutrient-poor water south along 
eastern Australia (Ridgway, 2007; Ridgway and Hill‘; 
Suthers et al., 2011). Originating in the Coral Sea with 
a southward flow, the EAC eventually forms the Tasman 
Front and a southward flowing eddy field (Ridgway and 
Hill*; Suthers et al., 2011). In contrast, southern Australia, 
bordered by the Indian Ocean, has strong coastal upwell- 
ing along the Bonney Coast, western Kangaroo Island 
(KI), and the southern coast of Eyre Peninsula, transport- 
ing cold, nutrient-rich waters to the surface (Kampf et al., 
2004; Middleton and Bye, 2007; Neuheimer et al., 2011). 
To examine if local environmental influences may 
be affecting the growth patterns of small pelagic fishes, 
growth chronologies were produced from otolith incre- 
ments of 2 commercially targeted small pelagic fish 
species—the common jack mackerel and redbait—from 
2 regions off southeastern Australia. Using a combination 
of length-at-age modeling and growth chronology mixed- 
effects modeling, we compared the growth rates of these 
4 Ridgway, K., and K. Hill. 2009. The East Australian Current. In 
A marine climate change impacts and adaptation report card for 
Australia 2009 (E. S. Poloczanska, A. J. Hobday, and A. J. Richard- 
son, eds.), Natl. Clim. Chang. Adapt. Res. Facil. Publ. 05/09, 16 p. 
