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Abstract

Winter sea ice plays a major role in the Antarctic ecosystem due to its influence on the
abundance and recruitment of keystone species and the secondary production associated
with the ice edge on which many Antarctic predators rely. For one of these predators,
the Weddell seal, long term data sets indicate that the population dynamics of this
species is closely tied up with the winter ice environment. However, very little
information exists on the winter movements of Weddell seals or their interactions with
the winter ice environment. Over 3 years, adult female Weddell seals were equipped
with satellite relay data loggers at Dumont d'Urville and the Vestfold Hills to determine
winter behaviour and the role of the local environment, including ice concentration and
weather, on this behaviour.
Satellite relay data loggers transmit information via the Argos satellite system
on seal location and behaviour. However, the ability to answer spatial questions of this
data and the role of the environment in animal movement is hampered by aspects of the
animal's behaviour and Argos location error. For Weddell seals, it was found that
haulout locations were over represented in the data set. As such, any spatial analyses
that include haulout locations of Weddell seals run the risk of overestimating the
importance of haulout sites. In addition, when extracting environmental information at
highly uncertain Argos locations, there is a high probability of extracting the wrong
information leading to inaccurate assessments of the role of the environment in animal
behaviour. A state-space modelling approach was applied to the Weddell seal tracks to
address this. The resulting locations were a vast improvement on Argos locations when
compared to GPS tracks of the same individuals and haulout locations were fixed to
avoid over estimation of their importance. The error distribution associated with each
location was incorporated into an approach whereby the extraction of a location specific environmental variable was weighted by the location's error distribution. This method
of extracting environmental variables was then applied to assess the role of the local
environment on the winter behaviour of Weddell seals.
The local environment influenced both winter haulout and foraging behaviour
with Weddell seals tending to haulout more under conditions of low wind speed and
higher temperatures and remain submerged when the opposite was true. Seals were also
more likely to terminate diving bouts under conditions of very heavy ice concentration
when compared to lighter ice concentrations in the fast ice environment. Whilst winter
foraging could be classed as either predominantly benthic or pelagic with a high level of
individual variability, all Weddell seals employed both foraging strategies at some stage
throughout the tracking period.
These results reveal that aspects of the local environment have the ability to
drive the winter behaviour of Weddell seals and must be considered in conjunction with
the influence of prey availability and larger scale climatic phenomena. Individual
foraging strategies imply that Weddell seals within the one population may display
varied responses to climate-mediated changes in prey availability. As such, Weddell
seals are vulnerable to changes in the ice environment that are long term and large scale
as well as short term and local.

Item Type:	Thesis - PhD
Authors/Creators:	Andrews-Goff, VL
Copyright Holders:	The Author
Copyright Information:	Copyright 2010 the author
Additional Information:	Thesis (PhD)--University of Tasmania, 2010. Includes bibliographical references
Related URLs:	Publisher
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