A rather odd-looking, robust whale, the southern bottlenose whale (Hyperoodon planifrons) is so-named for its short, tube-like beak, which sits below a large, bulb-shaped forehead. The crest of the head on the male becomes larger and heavier with age causing a change in the shape of the forehead, being flat and squared-off on older males, but rounded on the female and immature males (2). While the purpose of this enlarged forehead is unclear, it is thought that mature males may use it to head-butt each other during aggressive encounters (4). The small, sickle-shaped dorsal fin sits well behind the middle of the back, the flippers are small and blunt, and the tail flukes are un-notched (5)(6). The southern bottlenose whale varies in colour from chocolate-brown to yellow, being lighter on the flanks and underparts, due to the presence of photosyntheticalgae living on the whale’s skin (2)(6). Juvenile whales have distinctive, bold, white patches on the face separated by a dark stripe that also runs across the blowhole, and newborns are grey with dark eye patches and a white forehead (4). The southern bottlenose whale and its northerly namesake, the northern bottlenose whale (Hyperoodon ampullatus), are the only members of the genusHyperoodon(4).
As it is rarely observed at sea, very little is known about the biology of the southern bottlenose whale (5). Thought to be a deep diver, it is capable of remaining submerged for long periods of time, remaining at the surface for ten minutes or more in-between dives. It is typically observed in groups of less than ten individuals, although gatherings of up to 40 have been seen on some rare occasions (2). It is also thought to feed mainly on squid, although fish may also be eaten, as it migrates vast distances of over 1,000 kilometres in search of waters of waters with a seasonal abundance of prey (2)(4).
Mating may occur during summer, with a single calf born the following spring to early-summer. Like other beaked whales, it is likely that the southern bottlenose whale breeds once every few years, meaning reproduction is a slow process that potentially limits its ability to recover from a population decline. Maturity is probably reached at around 11 years of age and males live for more than 50 years, while females are known to live for over 37 years (6).
The southern bottlenose whale has a circumpolar distribution in the southern hemisphere, occurring throughout the southern Ocean (1)(7). In late summer it is thought to migrate northwards away from the Antarctic to more temperate waters, travelling as far north as South Africa, Brazil and western Australia (2)(8).
A whale of deep oceanic waters, the southern bottlenose whale is typically found in waters deeper than 1,000 metres and rarely occurs in water shallower than 200 metres (1)(6). During the summer it is often found within 100 kilometres of the edge of the Antarctic ice (1).
Unlike the northern bottlenose whale, which is one of the best-studied beaked whales, very little is known about the status of the southern bottlenose whale (9). Fortunately, however, it has never been exploited and, as a result of this, today it is thought to be the most common species of beaked whale in Antarctic waters, with the population estimated at approximately 600,000 individuals in 1995 (2). Potential threats to the species include bycatch in driftnet fisheries and discarded nets, pollution, which can lead to the accumulation of toxic substances in body tissues, and competition with squid fisheries at lower latitudes (1)(6). Like other beaked whales, the southern bottlenose whale is probably also highly sensitive to loud sounds caused by naval sonar and seismic exploration, which can lead to gas bubble disease (1)(10). It could also become threatened by rising sea levels and increased surface sea temperatures associated with climate change, although the way in which this may impact upon the species is currently unclear (11).
With such little known about the southern bottlenose whale, the major conservation need for this species is further studies on its abundance, distribution and behaviour (7). In Australian waters it is protected within the Australian Whale Sanctuary, and it receives further protection in the Southern Ocean Whale Sanctuary (6).
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Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
In the fishing industry, the part of the catch made up of non-target species.
The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
Capable of photosynthesis, a metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.
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