An Australian research team has documented something that many would have considered nearly impossible: A shark in the Southern Ocean just off Antarctica – on video, in its natural habitat. The footage comes from a baited deep-sea camera that was deployed near the South Shetland Islands (off the Antarctic Peninsula) at around 490 metres depth.
The footage shows a slowly swimming shark that experts assign to the sleeper shark family (Somniosidae). Which exact species it is cannot be determined from the images alone – sleeper sharks are very similar in external appearance. However, an independent expert considers it possible that it could be the southern sleeper shark (Somniosus antarcticus) – a species considered the ‘most southerly occurring shark’.
Why this clip is so special
Sharks are indeed extremely adaptable and widespread worldwide – the closer you get to the South Pole, the rarer direct records become. Although sharks occasionally appear as bycatch in sub-Antarctic fisheries, \”in situ\” observations (that is, in their natural habitat, not as bycatch) are truly exceptional in this region. According to ABC, only a few shark species have been recorded in the Southern Ocean around Antarctica so far – and video evidence from natural settings is practically non-existent.
What’s more: the animal was filmed in water at around 1.27 . For many marine creatures that is simply too cold – and even for cold-adapted sharks it is a limit we do not yet fully understand.
Sleeper sharks: predators of the cold and the deep
Sleeper sharks are regarded as deep-sea specialists: large, robust, with relatively small fins and often a marbled colouring. Much of what we know about the southern species comes from rare catches as bycatch. Fascinating (and rather astonishing): according to the report, the stomachs of southern sleeper sharks have repeatedly contained remains of giant squid – including those of the colossal squid, the heaviest known invertebrate.
Species puzzle: one shark or two?
Now the focus is on a question that has long occupied researchers: Are the southern sleeper shark and the Pacific sleeper shark truly separate species (–) or genetically (nearly) identical? The ABC piece describes that genetic evidence already calls this separation into question. To resolve this properly, genetic analyses (including eDNA from water samples and tissue samples) are to be expanded; a larger international project plans to collect new data for this purpose, among other places from the South Atlantic and the Indian Ocean.
How can sharks even ‘tolerate’ such cold water?
Around the Antarctic (and the Arctic), seawater can fall, because of its salt content, below 0 °C — down to about -2 °C. For most animals that would be lethal. In sleeper sharks the biochemistry probably looks like a ‘natural trick’: in the closely related Greenland shark, trimethylamine N-oxide (TMAO) and urea, among other compounds, have been suggested; they could act like a kind of ‘chemical antifreeze’. Exactly how this works in the southern sleeper sharks, however, is not yet fully understood.
