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Aspects of the ecology of Weddell seals Leptonychotes weddellii along the Mawson Coastline, East Antarctica

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Pike, Rhonda Jane 2006 , 'Aspects of the ecology of Weddell seals Leptonychotes weddellii along the Mawson Coastline, East Antarctica', Coursework Master thesis, University of Tasmania.

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Abstract

This study investigated the diet and patterns in occurrence of haul-out sites of Weddell
seals along the Mawson coast of East Antarctica.
Seats of Weddell seals (n = 303) were collected from 139 seal haul-out sites along 250
km of coast between Fold Island (Kemp Land coast - 66.83°S, 58.79°E) and Auster
Islands (MacRobertson Land coast - 67°25'S, 63°50'E) during 1998 to 2000.
Identification of species-specific hard parts from the seats found eighteen species of fish,
two species of octopod, two species of squid, and four species of crustaceans.
Randomisation analyses were used to determine associations between abundance of
primary prey species and year, season, geographic location and water depth at the sample
collection site. No significant interannual variation was found, but the diet varied
seasonally, as the squid Psychroteuthis glacialis featured more in the diet in the early
summer months compared to winter. Larger beaks of this squid were found in seats
collected from ice over deeper waters. The diet of Weddell seals along the Mawson coast
is therefore more diverse than reported for other parts of Antarctica and the diet also
varies seasonally and with changing bathymetry. The diversity in diet may be attributed
to the complex seafloor topography along the coast, allowing seals to forage within a
wide range of habitats at different depths.
For the investigation into patterns in occurrence of haul-out sites, three study areas were
established in 2000 at different locations along the Mawson coast. One study area
(Macey) had a high concentration of icebergs and islands, another area (Mawson) had
islands near the coast and fewer icebergs, and the third area (Colbeck) had very few
icebergs and no islands. Within each study area, there were two transects (1500m wide,
1500m apart) extending 20km north over the sea ice from the coast. Each study area was
surveyed three times - in winter (late July), late winter (mid September) and spring (midOctober).
Non-parametric tests were used to examine variation in density of haul-out
sites and density of seals with respect to distance to coast, between areas and between
survey periods. During the 3 surveys, 349 seals were observed amongst 165 sites across
all 3 areas. Friedman tests found no significant association of number of seal sites or
number of seals with distance to coast. Kruskall-Wallis tests found significant variation
between the three areas within each survey period; Macey consistently had more sites
than the other two areas. Friedman tests tested for temporal variation within each area,
however no significant changes in number of seal sites or number of individual seals
were detected. Although not formally tested due to small sample sizes, there appeared to
be no. spatial separation of sexes. Weddell seal holes were also used by emperor penguins
in the Macey and Colbeck areas and by crabeater seals in the Macey area.
This study implies that haul-out sites are not randomly distributed at the local scale (with
differences shown between different areas along the coast, ie, regional scale) and that
number of sites and number of seals hauled out on ice or seen in holes increases from
winter into the breeding season. The results suggest that density of seal sites in the fast
ice areas off the MacRobertson Land coast is affected by environmental factors such as
bathymetry and presence of icebergs.
This study suggests that local bathymetric features have an important influence on the
biology of Weddell seals in the Mawson area. Changing bathymetry is associated with
variation in diet. Water depth can also influence grounding of icebergs and ocean
currents that affect the physical structure and cracking of the sea ice, enabling Weddell
seals to access the ice surface to breathe and to haul-out for resting and pupping.

Item Type: Thesis - Coursework Master
Authors/Creators:Pike, Rhonda Jane
Keywords: Weddell seal, Weddell seal
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:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (MScSt)--University of Tasmania, 2006. Includes bibliographical references

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