The White Shark
Glenn Moore's blog | Created 6 years ago
The White Shark (Carcharodon carcharias)
The White Shark, otherwise known as the Great White or White Pointer, is one of the largest sharks. There are only two species of sharks known to exceed the White Shark in size and both are plankton feeders; the Whale Shark (Rhincodon typus) and the Basking Shark (Cetorhinus maximus).
The White Shark belongs to the order Lamniformes which also includes the Basking Shark, the Megamouth Shark, Mako Sharks, Porbeagles, Thresher Sharks, the Crocodile Shark, the Goblin Shark, and Sand Tiger Sharks.
How big do they get?
Females mature between 4 and 5 metres in total length and can reach 6 metres weighing as much as 2 tonnes. Males mature between 3.5 to 4 metres long and do not grow as large as mature females.
How long do they live?
In most lamniform sharks, annual growth bands are deposited within their back bones and these can be used to determine the age of the shark. Females mature between the ages of 12-17 and males between the ages of 7-9. White sharks are believed to live for almost 30 years.
Females gestate around 10 embryos. The mother produces additional unfertilised eggs that the newly-hatched sharks feed on in the uterus. Newborn free-swimming pups are estimated to be 1.2-1.4 metres long. With an estimated 18 months gestation period and a 3-year reproductive cycle, white shark populations are highly vulnerable to over fishing/culling.
White Sharks have huge serrated teeth, much bigger than those of other sharks of comparable size. They continually replace teeth with slightly larger ones as their jaws grow. As White Sharks increase in size their teeth become broader, and at a body length around 3 metres they begin to predate on marine mammals like seals and dolphins, in addition to fishes. White Sharks are commonly observed feasting on whale carcasses and preferentially feed on the blubber.
When are they most active?
Like other sharks feeding on large, highly mobile prey, White Sharks become more active during overcast days, or when water visibility is otherwise poor. Sharks do not depend solely on their sight to hunt prey, but more on smell and hearing, plus electroreception at close range, so reduced visibility enables them to get closer before they are detected. White Sharks maintain a variable body temperature 3-14˚C higher than the surrounding water by a heat-exchanging circulatory system. This enables them to hunt in waters too cold for other large sharks, such as Tiger Sharks. White Sharks are powerful swimmers and are known to jump out of the water as they attack seals at the surface.
Where do they live?
The distribution of white sharks is mainly in temperate, coastal waters, but they may also frequent waters around oceanic islands, especially near seal colonies, and sometimes occur in tropical waters. Tagging programs have revealed that large individuals undertake major migrations across the ocean basins and may dive down to 1,000 metres or more.
Who eats them?
Orcas, (killer whales) are the only animals in the oceans known to kill White Sharks. In 1997, an adult female orca, accompanied by a second adult female, was observed attacking and killing a 3-4 metre White Shark at Southeast Farallon Island, California. Following the attack the other White Sharks in the area disappeared and did not return until the following season.
White Sharks as top predators
Wherever they occur, adult White Sharks are typically at the top of the food chain. By preying on juveniles and reproducing adults that take unnecessary risks (for example seals swimming at the surface rather than along the bottom whenever possible), White Sharks play an important role in maintaining or even improving the fitness of prey species.
Ironically, the enormous jaws and large teeth that enable the White Shark to be such a formidable predator might eventually lead to its extinction. As rare top predators, White Sharks are usually not specifically targeted for their meat by shark fisheries. Their jaws and teeth however fetch very high prices on the black market. Even though they are protected by law in some areas, like Australia, they may be killed elsewhere as a result of their migratory lifestyle.
Evolution of white sharks
The origin of the White Shark and its relationship to the extinct shark megalodon (meaning mega-tooth) are controversial subjects in palaeontology. Megalodon, at an estimated adult length of almost 20 metres and a mouth big enough to swallow a small car, is justifiably regarded as the mother of all predators.
One theory is that megalodon is closely related to the modern White Shark (and was therefore named Carcharodon megalodon).
Another theory regards the two as only distantly related, belonging to separate families within the order Lamniformes.
In recent years, the latter theory has gained ground and most palaeontologists working on fossil sharks recognise Carcharocles as the valid genus name for the extinct megalodon.
The beginnings of the White Shark
The origin of the White Shark can be traced back to the Paleocene or earliest Eocene geological periods, about 55 million years ago. Molecular and palaeontological evidence indicate that White Sharks are a sister group of Mako Sharks and that the two groups separated from a common ancestor approximately 50-60 million years ago.
More about teeth
Sediments laid down in the ocean 2-7 million years ago but now exposed in the Peruvian desert preserve the transition from unserrated to serrated teeth in the White Shark lineage. The transformation took several million years as sharks evolve slowly compared to most other vertebrate groups.
In 2012, palaeontologists at the Western Australian Museum plan to explore 15-20 million-year-old rocks in the Southern Carnarvon Basin in search of fossil remains of Carcharocles megalodon and its favourite prey, baleen whales. Video clips and photographs will be uploaded on the Museum’s web site so you can follow the search for the ultimate super predator. Western Australia is already well known for its rich record of fossil sharks from the Cretaceous period (140-65 million years ago).