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Migrations of juvenile southern elephant seals from Macquarie Island

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van den Hoff, J (2002) Migrations of juvenile southern elephant seals from Macquarie Island. Research Master thesis, University of Tasmania.

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Abstract

I analysed tag resight and at-sea location data collected for juvenile (> 1 - 3 year-old)
southern elephant seals (Mirounga leonina) from Macquarie Island to establish these
particular objectives:
1. Identifying regions where the seals disperse to and/or migrate between.
2. Establishing a spatial scale for plotting and correlating geolocations with ocean
features and zones.
3. Recording the important foraging areas essential to the survival of these seals.
4. Quantifying the degree to which the seals share their marine habitat with
differing age groups and sexes of elephant seals, and with commercial fisheries.
Permanently marking seals provides information relating to haulout locality and
timing, migration duration and age related dispersal. Southern elephant seals
marked at Macquarie Island disperse to distant locations where they are sometimes
seen during their moult and, for juveniles, a mid-year haulout period (July-August).
Most (87%) of the seals resighted were within 1 OOO km of Macquarie Island, and
most, commonly at Campbell Island (700 km to the north-east). The sex and age
classes most likely to disperse there were males less than two years old. Male
elephant seals of all ages were resighted significantly more often than females, the
ratio being 2:1 (P > 0.05). Migration duration tended to increase with the seal's age
but migration distance was underestimated from resight observations when
compared with known telemetry records. Emigration from the Macquarie Island
population appears limited. From the resight effort at Campbell Island during 1995
the maximum proportion of the juvenile population from Macquarie Island to
haulout at Campbell Island was in the order of0.0053.
I tested the location estimation performance of geolocation time-depth recorders
(GLTDR) against a stationary site and free-ranging elephant seal locations
established by satellite and global positioning system (GPS) telemetry. I found
significant variation in latitude, but not longitude estimation, between individual
GLTDRs within the same deployment period. This indicates a high level of
confidence in longitude estimation if corrections for latitude are being made using
remotely sensed data (e.g., sea-surface temperature) and/or seal behaviors such as
dive depth and haulout. There was variability in location accuracy depending on season and latitude as previous studies have found. At-sea GLTDR derived location
estimates improved at higher latitudes where day length changes are greatest, seal
travel rates decrease and locations are clumped in presumed foraging areas or
haulout sites. Geolocation estimates improved as a consequence of deployment
period, longer stationary periods produced better estimates with greater confidence.
There was also considerable variation in daily location estimates of location during
non-equinox periods at a stationary site. These were related to some measured
weather conditions.
At-sea geolocations should be analysed using a scale of no less than± 2.5° (5°
grid square) at sub-Antarctic latitudes, and at least ± 2° (4° grid square) at higher
latitudes during non-equinox periods if a high level of confidence (95%) in position
estimation is required. For lesser degrees of confidence (68%), the scale can be
decreased to± 1.5° (3° grid square) at sub"'.'Antarctic latitudes and probably at higher
latitudes also, given that the accuracy of geolocation increases with increased
latitude. I conclude that geolocation is a very useful method for tracking the pelagic
movements of most land breeding marine birds, reptiles and mammals that make
long (ea. 1 OOO km) migrations to foraging grounds. The locations can be correlated
to meso-scale ocean features and similarly scaled commercial fishing areas.
Twenty-two juvenile southern elephant seals aged 7 to 14 months were tracked as
they departed Macquarie Island during 1993 and 1995. Migratory behavior and
areas of concentrated activity, presumed to be pelagic foraging grounds, were
established from location data gathered by attached geolocation time-depth
recorders. The seals ranged widely from the island preferentially migrating to the
south-east of Macquarie Island. Survivorship of seals that had been handled and
fitted with GLTDRs was similar to free-ranging seals of the same age that had no
instruments attached. Thus, the methodology used for this study appears to have no
detrimental effect on survival and this gives confidence in the results of this study.
Although not statistically tested, the foraging activity of seals appeared to be
associated with meso-scale oceanographic frontal systems and near bathymetric
features, especially waters near the Antarctic Polar Front (APF), the Southern
boundary of the Antarctic Circumpolar Current (SACC), the Marginal Ice-edge
Zone (MIZ), and the Campbell Plateau. Seals commonly foraged in waters greater than 3 OOO m deep where the sea-surface temperatures were between 1.0 and 4.0° C
unless they foraged over the Campbell Plateau where the sea-surface temperatures
were about 8° C and the depth less than 2 OOOm.
The foraging areas for juvenile seals overlap those of adult female seals but the
overlap is minimal in time and space because of the differing haulout behavior and
diving ability of the age classes. Adult male seals forage too far to the south to
overlap with juvenile seals of either sex but there appears to be an ontogeny of
differential foraging migrations with male seals from Macquarie Island similar to
that for northern elephant seals.
Southern elephant seals from Macquarie Island forage within managed fishery
areas and in the high seas, an area of unregulated fishing. The Convention on the
Conservation of Antarctic Marine Living Resources (CCAMLR) areas 58.4.1 and
especially 88.1 were important foraging areas for juvenile elephant seals from
Macquarie Island. Currently the overlap between fisheries and elephant seals from
Macquarie Island appears minimal, but there is a lack of knowledge of the diet of
southern elephant seals while at sea and in particular as they forage at the Antarctic
continental margin.

Item Type: Thesis (Research Master)
Keywords: Southern elephant seal
Copyright Holders: The Author
Copyright Information:

Copyright 2002 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:

Chapter 2 appears to be the equivalent of a post-print article published as van den Hoff, John (2001) . Dispersal of southern elephant seals (Mirounga leonina L.) marked at Macquarie Island. Wildlife Research 28 , 413–418

Date Deposited: 04 Feb 2015 23:28
Last Modified: 05 Apr 2016 00:05
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