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A dietary study of Moroteuthis ingens and other Southern Ocean squid species : combined stomach contents and fatty acid analyses

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Phillips, Katrina L.(Katrina Liddy) 2003 , 'A dietary study of Moroteuthis ingens and other Southern Ocean squid species : combined stomach contents and fatty acid analyses', PhD thesis, University of Tasmania.

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Abstract

The squid fauna are a key component of the Southern Ocean ecosystem, although unfortunately
little is known of their distribution, biology and ecology. While the biomass of squid in the
Southern Ocean must impose a large amount of predatory pressure on lower trophic levels, few
dietary data exist for any of the Southern Ocean species. Conventional dietary analyses of squid
are fraught with many sources of bias, and therefore this study has employed complementary
stomach contents and fatty acid analyses to investigate aspects of the diet of Southern Ocean
squid. The diet of the onychoteuthid Moroteuthis ingens was largely comprised of myctophid
fish, and the digestive gland of M. ingens was rich in lipid and found to be an ideal source of fatty
acid dietary tracers that are unmodified from the diet. Fatty acid dietary tracers were then applied
in combination with stomach contents analyses to investigate the temporal, spatial and sizerelated
dietary patterns of M. ingens. Using these complementary techniques, the diet of M.ingens
was found to vary significantly on an interannual and seasonal basis within the vicinity of
Macquarie Island, largely due to fluctuations in the proportions of myctophid fish species in the
diet. Moroteuthis ingens also exhibited spatial variations in diet among Macquarie Island, the
Falkland Islands, the Chatham Rise and Campbell Plateau (the latter two sites located within New
Zealand waters). The diet at the New Zealand sites was characterised by a proportion of
temperate myctophid species not identified at other sites, whereas squid collected from the
Falkland Islands consumed a much greater proportion of cephalopod prey. Lipid class and fatty
acid analyses also indicated that the diet varied considerably between the Chatham Rise and
Campbell Plateau, most likely due to the influences of different oceanographic regimes. Stomach
contents and fatty acid analyses of squid collected from the Falkland Islands indicated that M.
ingens switches from a crustacean- and cephalopod-based diet to a fish- and cephalopod-diet at
around 200 mm mantle length. Lipid class and fatty acid analyses of the other Southern Ocean
squid indicated that oegopsid species accumulate a large amount of lipid in the digestive gland.
This lipid has been determined to be of dietary origin, and will thus provide a rich source of fatty
acid dietary tracers applicable to future food-web studies of squid. Further consideration of the
mode of lipid and fatty acid storage in the digestive gland will be required before squid fatty acid
profiles can be reliably applied to dietary studies of higher trophic predators.

Item Type: Thesis - PhD
Authors/Creators:Phillips, Katrina L.(Katrina Liddy)
Keywords: Squids
Copyright Holders: The Author
Copyright Information:

Copyright 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 would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references

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