Leopard Seal (Hydrurga leptonyx)
A deadly hunter of the icy Antarctic seas, the leopard seal, so named for the cat like markings on their undersides, is one of the largest predators in the region, smaller than only the Killer Whale. Leopard seals are somewhat intimidating, with males reaching up to 300kg and a look that has been described as somewhat reptilian due to their eyes being positioned on the side of their heads rather than more forward facing like other seal species. In fact, when seen from certain angles, the leopard seal could almost be mistaken for a prehistoric sea monster with its sleek body and ferocious teeth!
Leopard seals are part of the Phocidae family, often called the true seals, and are the oldest of the modern-day pinnipeds, a diverse clade including a range of whiskered, fin footed semi aquatic mammals from walruses to sea lions. Their closest relatives are ursoids (bears) and musteloids (the family containing skunks, badgers, weasels and otters). Their ancestors were otter like In 2009, a beautifully preserved fossil discovery in Canada led researchers to uncover the earliest seal ancestors and the development of their aquatic lifestyles. Just over a metre in length with four strong legs, a short tail and flattened, likely to be webbed feet, the fossil was named Puijila and was a carnivorous, walking seal that swam and walked between 20 -24 million years ago. It is likely that this species wasn’t fully adapted for life in the seas, and so spent its time hunting in freshwater lakes and rivers, which is the evolutionary path by which seals became marine mammals. This evidence also points to the ancestral home of modern-day seals as the Arctic.
Antarctic Apex predators: the chilly lives of the leopard seal
Leopard seals inhabit the Antarctic continent and associated pack ice, although occasionally vagrants (a phenomenon in biology where individuals are found well outside their natural range) are occasionally sighted in far warmer climes, such as South Africa and Australia. Studies involving tagged seals have shown that they migrate between the sub-Antarctic islands and the Antarctic pack ice to make the most of the penguin and seal populations that make up their main prey source; although they are known to consume krill, cephalopods and fish. They have been known to predate fur and crabeater seals, making them the only pinnipeds whose diets consists of a substantial amount of warm-blooded prey. Their ecology and feeding behaviour is essential for understanding trophic cascades in the Antarctic; as an apex predator their impact on their habitat is huge.
Leopard seals are well designed for their role as an Antarctic apex predator. They have the longest jaws of any of the Phocidae with a mouthful of fierce canines and another set of specialised molars designed for sieving plankton from the water; this dual dentistry gives them the ability to make a meal out of everything from the microscopic plankton up to seals not much smaller than them. Their sharp teeth are also used to shred their unfortunate prey to pieces, as they don’t possess the ability to chew. They use their powerful flippers much like sea lions do, making them terrifyingly agile in the water. Although they have a fearsome reputation and there have been some unfortunate injuries caused to researchers and one very sad fatality of a scientist with the British Antarctic Survey, who was tragically killed whilst snorkelling, National Geographic photographer Paul Nicklen had a very different encounter. In 2012, whilst on an expedition in the Antarctic, Paul was photographing a leopard seal when it began to approach him with live, injured and then dead penguins. Some scientists believed this leopard seal was actually attempting to teach the photographer how to hunt or trying to feed him! Perhaps the seal thought this fellow was rather too skinny to be swimming in cold water and needed a bit of extra blubber!
Although they usually dive shallowly, they have been recorded diving deeper than 80 metres in search of a meal, a feat that requires them to have collapsible lungs and a reinforced trachea to prevent their airways being crushed under the pressure at such depths.
Fortunately, leopard seals are listed as least concern by the IUCN redlist. Although no direct impacts of climate change have been seen yet, it is very likely that leopard seals, like so many Antarctic and Arctic species, will suffer from loss of essential pack ice for pupping and hunting. In recent years, tourism in the Antarctic and Sub-Antarctic is increasing, and so far, we simply don’t know how this increased boat traffic will affect leopard seal behaviour and foraging. There is also the very real risk of injuries from boat collisions as boats often must squeeze through tight ice channels. Fortunately, leopard seals have been mostly protected from huge periods of commercial hunting due to their inaccessible habitat, and currently seal hunting is tightly regulated by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals.
Although leopard seals themselves aren’t under any specific threat right now, their icebound home is under severe threat from climate change and other newer threats like the increasing krill fishery industry, as well as new shipping routes and tourist trips as technology allows these distant, harsh places to become more accessible. Although these icy places seem very far away to us, their healthy function is essential to our global ecosystem resilience. Tiny microorganisms trapped in the ice absorb carbon dioxide from the air, acting as important carbon sinks, and whales and other marine species that migrate through these areas spread their faeces, contributing to vital nutrient cycles in the ocean. While human activity in the Antarctic regions increases, its important at this early stage that tight regulations are put into place to prevent further damage and keep these ecosystems as pristine as we can.
In an area that arguably receives less attention, the Antarctic and Southern Ocean Coalition has been working since 1978 to lead the way in Antarctic and Sub-Antarctic conservation. They are an environmental NGO that works to push for better policy, as well conducting research and monitoring the impacts of fisheries, tourism, bio-prospecting and climate change on these vast ecosystems.
Check out their website at https://www.asoc.org/ to learn about what this organisation is doing to protect the Antarctic and the species that call it home, and what you can do to help. They have practical tips on cutting down carbon emissions in your daily life, and how to eat a penguin friendly diet.
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Krause, D.J. Goebel, M.E. Marshall, G.J. and Abernathy, K (2016) ‘Summer diving and haul out behaviour of leopard seals (Hydrurga leptonyx) near mesopredator breeding colonies at Livingston Island, Arctic Peninsula.’ Marine Mammal Science, 32(3), pp 839-867
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