Abstract
Leopard seals are an important Antarctic apex predator that can affect marine ecosystems through local predation. Here we report on the successful use of micro geolocation logging sensor tags to track the movements, and activity, of four leopard seals for trips of between 142–446 days including one individual in two separate years. Whilst the sample size is small the results represent an advance in our limited knowledge of leopard seals. We show the longest periods of tracking of leopard seals’ migratory behaviour between the pack ice, close to the Antarctic continent, and the sub-Antarctic island of South Georgia. It appears that these tracked animals migrate in a directed manner towards Bird Island and, during their residency, use this as a central place for foraging trips as well as exploiting the local penguin and seal populations. Movements to the South Orkney Islands were also recorded, similar to those observed in other predators in the region including the krill fishery. Analysis of habitat associations, taking into account location errors, indicated the tracked seals had an affinity for shallow shelf water and regions of sea ice. Wet and dry sensors revealed that seals hauled out for between 22 and 31% of the time with maximum of 74 hours and a median of between 9 and 11 hours. The longest period a seal remained in the water was between 13 and 25 days. Fitting GAMMs showed that haul out rates changed throughout the year with the highest values occurring during the summer which has implications for visual surveys. Peak haul out occurred around midday for the months between October and April but was more evenly spread across the day between May and September. The seals’ movements between, and behaviour within, areas important to breeding populations of birds and other seals, coupled with the dynamics of the region’s fisheries, shows an understanding of leopard seal ecology is vital in the management of the Southern Ocean resources.
Highlights
MethodsAll animal procedures were approved by the British Antarctic Survey Animal Welfare Board
All seals appeared to undertake a number of shorter range trips, that varied in distance around a central place on Bird Island: including short trips (~100 km) in an around the shelf break region, or longer trips (~300–500 km) northwards to the Polar Frontal Zone or southwards (Fig 1)
A comprehensive understanding of the timings of leopard seal movements and the factors influencing their haul out behaviour is important both to enable robust population size estimates and to assess their role in the Southern Ocean ecosystem
Summary
All animal procedures were approved by the British Antarctic Survey Animal Welfare Board. Micro global location sensor data loggers (GLS, MK 7, 7 x 20 x 19 mm, mass < 4 g) were deployed on leopard seals at Bird Island, South Georgia (54.01 ̊S and 38.05 ̊W) during the austral winter. The GLS were fixed to a Dalton jumbo roto tag and attached to the inter-digital webbing of the hind flipper so that the GLS protruded beyond the edge of the webbing. Loggers were fixed to the Dalton tags using epoxy adhesive and cable ties prior to their attachment to the animals. The leopard seal was approached whilst hauled out and sleeping, and the tag deployed using specialist application pliers. Animals were sexed and the standard length (nose to tip of tail) estimated by measuring adjacent to the sleeping animal
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