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Response to change in the environment : population dynamics of Weddell seals in east Antarctica


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Lake, Samantha Elizabeth (2007) Response to change in the environment : population dynamics of Weddell seals in east Antarctica. PhD thesis, University of Tasmania.

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In this thesis, two inter-related hypotheses were explored: The first hypothesis was that Weddell seals
forage over small spatial scales (10s to 100s ofkilometers) and therefore experience, rather than move
to avoid, resource limitation. The second hypothesis was a consequence of the seals experiencing
periods of resource limitation i.e. that changes over time in resource availability affect the seals' annual
rates of survival and reproduction so that these parameters can be used as indicators of foraging
Diet study supported the premise that Weddell seals forage over relatively small spatial scales. Prey
types were characteristic of the continental shelf. Many prey types were from inshore habitats. There
was regional, temporal and fine-scale variation in the diet indicating that seals were foraging nearby
where seats were collected. However, the wide variety in potential prey types may minimize coupling
between Weddell seal population dynamics and the abundance of any particular prey species.
Ground studies and satellite tracking from mid-winter showed that Weddell seals rest in areas of fast
ice. There was indirect evidence for seals foraging further offshore in that many haul-out sites were
adjacent to a lead of open water within which the seals could have traveled through the dense sea ice
zone. The three tracked seals did rest regularly on coastal fast ice, suggesting that they were foraging
within a limited area. Limited movement may be a behavioural strategy to navigate by spatial memory
in the dark of Antarctic winter. Furthermore, evidence suggests that local seals communally use and
maintain breathing holes in static ice, which may make access to and from the water reliable, despite
temperatures well below freezing.
Multi-strata models showed that the proportion of females in breeding state did change over time.
Breeding proportion averaged 0.70 per annum, and ranged from 0.53 to 0.88 per annum. This
contrasts with the relatively small magnitude of temporal variability in probability of parous females
surviving from year to year, and is qualitatively similar to temporal variation in probability of pups
surviving first year of life. The magnitude of inter-annual variability in both the probability of
producing a pup, and the probability of that pup surviving, demonstrates how tenuous each
reproductive event is for this long-lived mammal species.
Better understanding of the teleconnections between El Nino - southern oscillation (ENSO) and local
physical and biological processes might elucidate the loose connections sometimes observed between
ENSO and Weddell seal reproduction. At this stage, it is simply noted that the longest El Nino
(warm) event in the record of 113 years (1990-1995), closely followed by another very severe El Nino event (1997), did coincide with low reproductive rates of Weddell seals at the Vestfold Hills
throughout the last decade of monitoring. In general, evidence suggests that the purported trend for
increasing frequency and intensity of El Nifio events could be detrimental to Weddell seals and the
inter-dependent aspects of Antarctic ecosystems.

Item Type: Thesis (PhD)
Keywords: Weddell seal, Weddell seal
Copyright Holders: The Author
Copyright Information:

Copyright 2007 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:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2007. Includes bibliographical references. 1. Introduction -- 2. Regional, temporal and fine-scale spatial variation in Weddell seal diet at four coastal locations in east Antarctica -- 3. Spatial utilisation of fast ice by Weddell seals Leptonychotes weddelli during winter -- 4. Movements of adult female Weddell seals during the winter months -- 5. Interannual variation in reproductive rate of Weddell seals at the Vestfold Hills, Prydz Bay, east Antarctica, 1973-2000 -- 6. Synthesis and conclusions

Date Deposited: 19 Dec 2014 02:51
Last Modified: 27 Mar 2017 04:37
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