The great white shark, Carcharodon carcharias, is the largest predatory fish, reaching about six metres. It is warm-blooded in a limited and important sense, it detects electric fields, it lives far longer than was believed until recently, and its reputation is the product of one novel and one film rather than of anything the animal does.
Adult great whites commonly run four to five metres and roughly a tonne, with the largest reliably measured individuals around six metres; females are larger than males. The body is a classic mackerel-shark shape, thick through the middle and tapering hard, with a crescent tail that gives thrust with little drag.
The colouring is countershading: dark grey above, white below, so the animal disappears against the dark seabed from above and against the bright surface from below. It is the name of the shark and it is also its principal hunting advantage.
Teeth are serrated triangles, arranged in rows that rotate forward continuously as they are lost. A great white goes through many thousands in a lifetime, which is why shark teeth are among the most common vertebrate fossils.
Great whites are regional endotherms. A countercurrent heat exchanger called the rete mirabile, a dense interleaving of arteries and veins, retains the heat generated by swimming muscle instead of losing it at the gills. Muscle, stomach, brain and eyes are held well above the surrounding water, in some measurements by ten degrees or more.
This is expensive and it buys two things: faster muscle contraction, and the ability to hunt in cold water without the sluggishness that would otherwise impose. It is why great whites range from the tropics to water near the freezing point, and it is a solution reached independently by tuna and by a handful of other sharks.
The other distinctive sense is electroreception. The ampullae of Lorenzini, jelly-filled pores concentrated around the snout, detect voltage gradients as small as a few billionths of a volt per centimetre, which is enough to find the muscle activity of a fish buried in sand. At close range, when the shark rolls its eyes back for protection during a strike, this is the sense it is using.
Juveniles eat fish and rays. The switch to marine mammals comes with size, at roughly three metres, and coincides with changes in tooth shape and jaw strength.
The hunting of seals at places such as False Bay in South Africa and the Farallon Islands produced the familiar breach: an ambush from directly below at speed, carrying the shark out of the water. It is spectacular and it is also a small part of the animal's normal behaviour.
Bites on humans are rare, and the pattern is informative: most are a single bite followed by withdrawal, and most victims survive. The animal is not built to eat a person; a human has too little fat to be worth the energy of a hunt, and the usual reading is investigation followed by rejection. Fatalities occur mainly through blood loss from that single bite. Roughly five to ten people worldwide die from shark bites of all species in a typical year.
Age was estimated for decades by counting growth bands in the vertebrae, on the assumption of one band a year, giving lifespans of around twenty-five years. Radiocarbon dating of those bands, published in 2014 and using the bomb-testing carbon spike of the 1950s and 1960s as a marker, showed that assumption was wrong: the oldest male in the sample was about seventy-three.
That single correction changes the conservation arithmetic completely. Great whites mature late, around twenty-six years in females, carry their young for something like eighteen months, and produce small litters of a few pups. Reproduction is ovoviviparous with oophagy, meaning embryos hatch inside the mother and eat unfertilised eggs. A population like that cannot absorb adult mortality and cannot recover quickly from it.
The great white is commonly described as a small surviving megalodon. It is not, and this is one of the more persistent errors about it.
Otodus megalodon, which reached perhaps fifteen to eighteen metres and died out around 3.6 million years ago, belongs to the otodontids, an entirely separate family. The great white's ancestry runs through the broad-toothed mako lineage, Carcharodon hastalis, and the two groups overlapped in time rather than succeeding one another. The resemblance of the teeth is convergence on the same job.
Between roughly 2015 and 2018, great whites effectively disappeared from False Bay and Gansbaai in South Africa, sites that had been among the most reliable in the world for seeing them.
The explanation with the strongest direct evidence involves orcas. Two males known as Port and Starboard have been repeatedly recorded killing white sharks along that coast and removing the livers, and shark departures follow their arrivals closely, with carcasses washing ashore precisely mutilated. Predation risk driving a fear response across a whole population is well documented in other systems.
It is not the only account offered. Others point to heavy historical removal by shark nets and drumlines, to declining prey, and to a longer-term redistribution eastward along the coast that predates the orcas. The most defensible summary is that orca predation is well evidenced and is probably not the whole explanation.
The great white is Vulnerable and protected in many jurisdictions including South Africa, Australia, the United States, Namibia and Israel, and listed on CITES Appendix II. Global numbers are hard to establish and estimates are poor.
The pressures are bycatch in longline and gillnet fisheries, targeted killing for jaws and teeth, and shark control programmes: nets and drumlines set off beaches in Australia and South Africa kill white sharks along with a large volume of other marine life, and their effectiveness at preventing bites is contested.
Finning is the broader problem for sharks generally. Tens of millions are killed annually across all species, and a slow-breeding animal cannot sustain that. Several populations of oceanic sharks have declined by more than seventy per cent since 1970.
The reputation is worth stating plainly, because it has had consequences. Peter Benchley's novel in 1974 and Steven Spielberg's film in 1975 produced a durable and largely inaccurate public picture, and were followed by a measurable rise in trophy shark fishing along the US east coast. Benchley spent much of the rest of his life on shark conservation and said he could not have written the book knowing what was later established. The animal in the film does not exist; the animal that does is a slow-growing, late-maturing fish that is being removed faster than it can replace itself.
