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Mesoscale characterisation of the Pelagic Shelf ecosystem of south-eastern Australia : integrated approach using larval fish assemblages and oceanography


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Keane, John Patrick 2009 , 'Mesoscale characterisation of the Pelagic Shelf ecosystem of south-eastern Australia : integrated approach using larval fish assemblages and oceanography', PhD thesis, University of Tasmania.

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This represents the first mesoscale study linking larval fish assemblages and water masses off
south-eastern Australia, aimed at characterising the pelagic shelf ecosystem within the region.
Data were collected during five intensive ichthyoplankton surveys carried out between 24.6°S
and 41.7°S (-1050 nm), that included the coastlines of southern Queensland (Qld), New
South Wales (NSW), eastern Victoria (Vic) and north-eastern Tasmania (Tas). Surveys were
conducted in spring 2002 and 2003 (Qld-NSW), summer 2003 (NSW-Tas), summer 2004
(NSW-Vic) and winter 2004 (Qld-NSW). A total of 371 vertical plankton samples were
obtained via a bongo sampler simultaneously with physical oceanographic variables to a
maximum depth of 200 m.
A novel multivariate approach was developed and employed to define water masses using
temperature frequencies from OTD-derived profiles. While this approach departs from
traditional methods, it proved to be an effective and objective method of delineating water
masses, even when indistinct current structures existed. Up to three discrete water masses
were identified during individual surveys, namely East Australian Current (EAO) to the
north, Tasman Sea (TAS) to the south, and a mixed water mass (MIX) containing EAOTAS
water in between.
Surveys yielded a total of 24,135 larval fishes representing 150 taxa from 101 families.
Epipelagic taxa dominated the larval fish community contributing 41-633 to the total
numbers caught across each survey, with Trachurus spp. (27.73), Sardinops sagax (17.93)
and Lophonectes gallus (3.83) being most abundant. Distinct larval fish assemblages
identified via multivariate analyses corresponded directly to identified water masses in terms
of their spatial distribution. Assemblage composition differed significantly between water
masses, with EAO and TAS being most dissimilar. Such contrast was due to tropical, subtropical
and temperate taxa in EAO, primarily temperate taxa in TAS, and a combination of
EAO and T AS taxa within MIX, the latter being consistent with the convergence of both
water masses. Discriminator taxa between the recurrent EAO and TAS assemblages included
labrids and Bregmaceros spp. in EAO, as well as L. gallus and Macroramphosus spp. in TAS.
Further, both water mass and assemblage boundaries were found to be dynamic, shifting
spatially and temporally depending on the strength of the EAO.
Analyses on individual taxa revealed larval habitats pointing to distinct water mass
preferences, while water mass interfaces often acted as a barrier to larval dispersal. Moreover,
habitats of the abundant small pelagic taxa, namely Etrumeus teres, S. sagax, Engraulis
australis, Trachurus spp. and Scomber australasicus, were similar, and appeared closely
linked to the extent, strength and timing of the seasonal EAO cycle.
Overall results highlight the strength of integrating ichthyoplankton dynamics and
oceanography, and set a foundation for future adaptive biophysical surveys, particularly in
relation to understanding larval transport mechanisms and spawning stock habitats for key
pelagic species. Ultimately, links between biological and physical factors will assist in
understanding the potential effects of climate change on the distribution and abundance of
fish stocks within the region.

Item Type: Thesis - PhD
Authors/Creators:Keane, John Patrick
Copyright Holders: The Author
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Copyright 2009 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Additional Information:

Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2009. Includes bibliographical references

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