The question of whether sharks inhabit the waters of Antarctica has a straightforward answer: no. The vast majority of the world’s 500-plus shark species are absent from the shallow continental shelf waters surrounding the continent. While a few deep-dwelling relatives may occasionally venture into the outer boundaries of the Southern Ocean, the characteristic large, predatory sharks found elsewhere do not establish a permanent presence here. This absence is the result of millions of years of evolutionary history combined with two formidable natural barriers: a massive ocean current and a severe physiological hurdle posed by the freezing water. Sharks simply cannot survive or successfully colonize this environment.
The Polar Front and Geographic Isolation
The primary physical reason for the lack of sharks is the Antarctic Circumpolar Current (ACC), the world’s largest ocean current. This powerful, eastward-flowing current circles the entire continent, acting as a thermal fence that isolates the Southern Ocean from warmer oceans to the north. The ACC creates a distinct boundary known as the Antarctic Polar Front (APF), where surface water temperatures drop sharply, often by 2 to 5 degrees Celsius. This thermal discontinuity prevents the southward migration of most temperate and warm-water shark species. The current extends from the surface to the seabed, creating a deep-water moat of frigid water that blocks access to the Antarctic ecosystem.
The Physiological Challenge of Sub-Zero Water
Even if a shark were to breach the Polar Front, it would face a severe biological problem: the water temperature. Seawater on the Antarctic shelf remains consistently near its freezing point of approximately -1.87 degrees Celsius. To survive in water this cold, most Antarctic fish have evolved a unique defense mechanism: antifreeze glycoproteins (AFGPs). These specialized proteins circulate in the blood, binding to the surface of ice crystals to prevent them from growing and thus lowering the internal freezing point of the fish’s body fluids. Sharks, however, belong to a group of fish called elasmobranchs, which use a different osmoregulatory strategy. They retain high concentrations of urea in their tissues to match the salinity of seawater, preventing dehydration. The complex chemistry of AFGPs appears incompatible with this high-urea system, making sharks physiologically incapable of surviving the sustained sub-zero temperatures.
The Dominant Fish of the Southern Ocean
The ecological niche sharks occupy elsewhere remains largely empty in the Antarctic, but the Notothenioids have risen to dominance. This group, which includes the Antarctic cod and icefish, accounts for nearly 90% of the continental shelf fish biomass. These bony fish successfully evolved the AFGPs that sharks could not, allowing them to thrive in the frigid waters. Notothenioids also developed other adaptations, such as losing their kidneys’ glomeruli to retain costly AFGPs. The icefish went further, losing red blood cells and hemoglobin, which allows their blood to flow more easily in the cold.
Skates, Rays, and Deep-Sea Relatives
While true sharks are absent from the Antarctic continental shelf, a few cartilaginous relatives do exist. Skates, flattened relatives of sharks, are the only elasmobranchs known to successfully inhabit the frigid, near-shore waters of the Antarctic continent, with seven species endemic to the Antarctic Convergence. In the outer boundaries of the Southern Ocean, deep-sea sharks are occasionally encountered in deep trenches and slopes. Footage has been captured of the Southern Sleeper Shark (Somniosus antarcticus) at depths of around 500 meters in the South Shetland Trench, marking the most southerly confirmed sighting of a true shark. This species survives because the water at that depth is slightly warmer than the surface, creating a localized “warm corridor.”