Migrations of juvenile southern elephant seals from Macquarie Island

• Main Author: van den Hoff, J
• Format: Thesis
• Language: English
• Published: 2002
• Subjects: Southern elephant seal; Antarctic; Campbell Island; Campbell Plateau; The Antarctic; Antarc*; Elephant Seal; Elephant Seals; Macquarie Island; Mirounga leonina; Southern Elephant Seal; Southern Elephant Seals
• Online Access: https://eprints.utas.edu.au/22081/; https://eprints.utas.edu.au/22081/1/whole_VandenHoffJohn2002_thesis.pdf

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.