Long term movements and activity patterns of an Antarctic marine apex predator: The leopard seal

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.

Summer circumpolar acoustic occurrence and call rates of Ross, Ommatophoca rossii, and leopard, Hydrurga leptonyx, seals in the Southern Ocean

“…from Antarctic krill, fish, to larger vertebrates; Rogers and Bryden 1995;Hall-Aspland and Rogers 2004;Forcada et al 2012;Krause and Rogers 2019). The close association of high numbers of leopard seal calls and the sub-Antarctic Circumpolar Current could indicate that these polar front waters provide suitable foraging habitats for this species (Staniland et al 2018). Such offshore detection of leopard seal sounds in summer could also suggest the southward migration of some seals from the sub-Antarctic islands to the Antarctic pack ice (Nordøy and Blix 2009;Rogers 2009;Staniland et al 2018).…”

“…The close association of high numbers of leopard seal calls and the sub-Antarctic Circumpolar Current could indicate that these polar front waters provide suitable foraging habitats for this species (Staniland et al 2018). Such offshore detection of leopard seal sounds in summer could also suggest the southward migration of some seals from the sub-Antarctic islands to the Antarctic pack ice (Nordøy and Blix 2009;Rogers 2009;Staniland et al 2018). Female southern elephant seals were observed to use the eddy fields of the Antarctic Circumpolar Current to reduce transport energy costs during foraging and migration (Massie et al 2016), these seals might also follow suit.…”

“…Ross seals, for most of the year, are pelagic and inhabit the open ocean north of the pack ice, but move south into the dense pack ice to pup, breed and moult (Blix and Nordøy 2007;Thomas and Rogers 2009;Southwell et al 2012) whereas, leopard seals inhabit the Antarctic pack ice yearround (Rogers et al 2005;Southwell et al 2008b;Rogers 2009;Meade et al 2015;Staniland et al 2018). Compared to leopard seals, Ross seals are more vulnerable to sea ice loss due to climate change, since they are more dependent on the dense consolidated pack ice to rest, pup and avoid predators (Learmonth et al 2006;Siniff et al 2008;Bengtson et al 2011).…”

“…Compared to leopard seals, Ross seals are more vulnerable to sea ice loss due to climate change, since they are more dependent on the dense consolidated pack ice to rest, pup and avoid predators (Learmonth et al 2006;Siniff et al 2008;Bengtson et al 2011). Although most leopard seals inhabit the Antarctic pack ice year-round (Rogers et al 2005;Rogers 2009;Meade et al 2015) some animals move north, out of the pack ice, to sub-Antarctic islands (Rogers 2009;Staniland et al 2018). Leopard seals are more plastic in their substrate use; where they typically haul-out on the ice floes in the pack ice, they will also use sandy beaches of the sub-Antarctic islands and the southern continents (Rogers 2009).…”

Classifying grey seal behaviour in relation to environmental variability and commercial fishing activity - a multivariate hidden Markov model

“…bathymetry, sediment type and slope) and dynamic (e.g. sea surface temperature and salinity) environmental variables known to influence marine mammal movement behaviour 29,30 and fitted these directly into a multivariate HMM to assess variation in movement behaviour while at sea. To quantify movement behaviour of grey seals near commercial fishing operations, we included proximity to active fishing net locations in real time as a dynamic covariate in the analysis.…”