Wildlife of the South Orkney Islands
By Rowena Mynott
Originally named the Powell’s Group after the two sealers who discovered them in 1821. The South Orkney Islands were given their present name a couple of years later in 1823 as their latitude is roughly the same as their namesake – the Orkney Islands, in Scotland.
Becoming the world’s first ‘high seas’ marine protected area in May 2010, the South Orkneys cover 94,000 square kilometres of chilly Southern Ocean. This protection prevents fishing and waste disposal in the area as well as providing increased opportunities and improved coordination for scientific research activities. Scientists have recently discovered that these barren looking islands may in fact have more biodiversity than the Galapagos Islands.
The southerly location means that about 90% of the islands are glaciated. Fauna inhabiting these environments is similar to those found in the Arctic such as marine mammals and oceanic birds.
The Southern Orkneys mark the southern limit of The WeddellScotia Confluence – an area where the outflowing Weddell Sea waters converge with the eastward flowing waters of the Scotia Sea. This area is a key habitat for the heavily harvested and heavily relied upon food source – Antarctic krill.
Antarctic Krill – Euphausia superba
These little creatures are so small that an area of just one cubic metre can contain up to 30,000 individuals. Although small, Antarctic krill are actually the largest of the species at around six centimetres long, making them quite visible to the naked eye. As crustaceans, their shells are often transparent allowing an insight into their last meal: microscopic plants known as phytoplankton.
Krill are, in terms of biomass, the most abundant species in the world. They are near the bottom of the food chain and are responsible for feeding the majority of life in the ocean, either directly or as food for larger predators.
As a keystone species their decline in the ocean environment would have dramatic knock-on effects. Unfortunately, over the years, scientists have been witnessing such a decline. It is believed that over the past 35 years krill numbers have decreased by 80%.
The calcareous tests of krill are susceptible to ocean acidification and although little is known at the moment about how this affects krill, other species with a calcareous exoskeleton are severely compromised. Scientists have recently identified devastating effects of increased ocean acidity on . Up to 54% of the larvae did not survive with increased acid levels. This is particularly worrying for Antarctic krill as ocean acidification is notably worse in the polar regions.
Krill are targeted catch by fisheries for use in animal food and fish bait products. The Antarctic krill fishery nets around 100,000 tonnes of krill per year with the main consumers being Asia and Scandinavia.
Weddell Seal – Leptonychotes weddellii
From one of the smallest creatures in the ocean to a much larger one, the Weddell seal grows to 3.5 metres and 600 kilograms feeding mainly on krill, fish and squid. They are well known for their incredible diving abilities, diving to 750 metres to forage for food in and around icebergs. A high level of myoglobin in their muscles allows these seals to stay submerged for up to eighty minutes at a time. Living in Antarctica in winter is difficult and despite such a great ability to hold its breath, the seals are well aware that they need to return to the surface to breathe. Being trapped under the ice is a real issue, so by using their long canines to rasp away at the icebergs, the seals create new breathe-holes.
With healthy population numbers – around 800,000 individuals – these animals are heavily researched. Although these seals have been on the decline recently, population numbers are considered stable. Their main predators are larger marine mammals such as the orca.
Weddell seals will give birth to one pup at a time, however they have a unique ability called delayed implantation. A seal can be carrying a fertilised egg that goes into a suspended state for up to 90 days before implanting. If the mother’s body is in a poor state or she is under severe stress the blastocyst will be reabsorbed into her body. If she is fit and well she will become pregnant. Pups are fully self sufficient by around six weeks of age.
Grey-headed Albatross – Thalassarche chrysostoma
Species of the albatross family are the largest of all sea birds. A two-metre wingspan enables them to glide for long distances without expending much energy, something that is vital to an individual’s survival as they are largely pelagic birds, choosing to forage in open ocean and only coming ashore to breed.
They are legendary birds particularly to sailors, notably from the poem Rime of the Ancient Mariner written by the English poet Samuel Taylor Coleridge in 1797 that describes the experiences of a sailor who has returned from a long voyage. As the sailor’s ship is pushed off course towards Antarctica by bad weather, an albatross appears and leads the ship to safety. Much to the despair of the crew, the mariner shoots the bird leading to an ongoing saga of curses. The crew forces the mariner to wear the albatross around his neck (which is where the modern saying originates from) and upon the death of his crew he is forced to wander the Earth, telling his story and teaching a lesson as penance for shooting the albatross.
Unfortunately, these days, the albatross is not regarded in such high esteem. Rapidly declining numbers have put this bird on the IUCN list as Vulnerable. Longline fisheries have a significant impact on these birds as they become snared upon the hooks and are dragged under the water. The slow reproduction rate of the albatross only serves to worsen the problem. It is believed there are around 250,000 individual grey-headed albatross currently but that the population has decreased by up to 49% over the last 90 years.
Leopard Seal – Hydrurga leptonyx
Named for its spotted coat and its ferocity, the leopard seal is the second largest seal in the Antarctic and the largest of the phocid (or ‘true’) seals – meaning they have no external ear flaps.
Living for around 25 years, these seals have few predators. , Humans were once the largest predator, however these days orcas are the main predator. Whilst there are not many reports of incidents with humans, these days it is advisable to give the leopard seal the respect that it deserves, particularly as it is the only seal to hunt on warm-blooded prey such as other seals.
Living a solitary life on the pack ice, leopard seals are also quite the nomads of the seal kingdom. Whereas most Antarctic seals do not leave the confines of the cooler waters around Antarctica, the leopard seal has been seen as far north as Tasmania and even in the warm waters of Heron Island in Australia.
Females are larger than the males and weigh up to 500 kilograms. After digging a hole in the ice for the pup to rest, they will give birth to a single offspring upwards of about 30 kilograms before returning to the ocean to forage.