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Determining the unknown in Southern Ocean squid : distribution and diet of Histeoteuthis eltaninae and Martialia hyadesi


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Hughes, Amanda Rose 2010 , 'Determining the unknown in Southern Ocean squid : distribution and diet of Histeoteuthis eltaninae and Martialia hyadesi', Honours thesis, University of Tasmania.

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In the Southern Ocean, cephalopods are infrequently captured by conventional samplingmethods,
but this is not a reflection of their abundance. This inadequacy has resulted in their being limited
knowledge into cephalopods despite their importance as voracious predators and a key prey
resource to apex predators. These predators have allowed for a newtechnique to be developed
through using theirstomach contents to obtain cephalopods resistant mouthparts (known as beaks).
In the Southern Ocean, juvenile elephant sealshavethe greatest divingand foraging capacity,
resulting in the greatest representation of the cephalopod community in their stomach contents.
These beaks are morphologically uniqueto a species, withthe dimensions related to the size the
whole animal, allowing for species specific knowledge that can be relatedto size. Diet, potential
prey and distribution can be determined through stable isotope analysis.
Stable isotope analysis was conducted ontwo predominate species found in the stomach contents
ofjuvenile elephant seals at Macquarie Island. Histioteuthis eltaninae was the most predominate
cephalopod species and is believed to have a life span of approximately oneyear. Over this year
period, 5'^C signatures indicated thatthere was no active migration occurring, resulting in all life
stages inhabiting thesame broader region. H. eltaninae distribution is relatively confined to waters
around Macquarie Island andappears to berestricted bytemperature. The5''N value indicated a
positively linear relationship between trophic level andsize of the individual. However, as
expected in anannual species, this relationship was effected byseason. Despite these relationships,
the most predominant prey item appears to correspond withmyctophid fish.
Martialia hyadesi was also investigated andappears to have a minimum life span of 16months
indicated bythetwo concurrent size classes occurring between September andDecember. The
stable isotope analysis demonstrated a broad distribution that involved extensive migration from
southern, almostAntarcticwaters to waters north of Macquarie Island. Thereforethis speeies must
withstand a great diversity of temperatures, particularly when compared to H. eltaninae. When
eonsidering trophic level andpotential prey resources, there appears to be a shift from one tropic
level, such as crustaceans and myctophid fish when individuals were smaller, to largerfish and
othercephalopods, approximately the nexttrophic level up in larger individuals. M hyadesi appear
to utilize lower trophic levels to a greater extent thanH. eltaninae, potentially the resultof M.
hyadesi opportunistic nature.

Item Type: Thesis - Honours
Authors/Creators:Hughes, Amanda Rose
Keywords: Squids, Squids
Copyright Holders: The Author
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Copyright 2010 the Author - The University is continuing to endeavour to trace the copyright
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Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (BMarSc)--University of Tasmania, 2010. Includes bibliographical references

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