I am very surprised that I have not blogged about great white sharks yet. After all, I doubt there is a more well-known species of shark than the great white. I think hammerheads come a close second, but I’m betting great white sharks are the species that comes to most peoples’ minds right away. That being said, I don’t think many people know a whole lot about great white sharks, only that they exist. So today we’ll talk about these impressive killers.
Though they have a broad distribution, there are certain places where great white sharks are commonly found. These are in the US, South Africa, Japan, Oceania, Chile, and the Mediterranean Sea. They prefer waters between 12 and 24 degrees Celsius, and though they are generally found on the coast, great whites have been observed in the open ocean and to depths of 1,200 m. So basically, if you’re in the ocean and the temperature is reasonably balmy, there’s a possibility a shark is watching you.
Great white sharks are very large fish, with females averaging lengths of 4.57-4.88 m, while males are slightly smaller, at 3.35-3.96 m. The largest great white recorded reached a staggering 6.1 m in length. The only other cartilaginous fish that are larger than great whites are whale sharks, basking sharks, and giant manta rays, which are all nice, docile filter-feeding fish. Thus, the great white has the dubious honour of being the largest living macropredatory fish.
Great whites are marvellously adapted to their predatory lifestyle. They have grey-blue colouring on their backs, and a white underbelly, which makes it difficult for prey to detect them in the water. Their ampullae of Lorenzini allow them to sense electromagnetic fields caused by the movement of animals in the water. This sense is so acute that they can detect the heartbeat of a stationary animal at close range. Apparently even staying still won’t protect you from a great white.
One of the difficulties about being a predator in the ocean is keeping warm, so you can move quickly when needed. Great whites solve this problem by having a system of closely packed arteries and veins on the sides of their bodies. When they move, the muscles heat up the veinous blood, which in turn raises the temperature of the incoming arterial blood.
Though most great whites are solitary, there are some that live in small groups of two to six animals. In these groups, the sharks form dominance hierarchies, with females dominating males and bigger sharks dominating smaller ones. Most conflicts between great whites are resolved peacefully, but bite marks have been seen on some sharks, suggesting that sharks may sometimes establish dominance through biting.
Great white sharks eat a large variety of food, and what prey they prefer depends on their size. Young sharks eat mostly fish and other sharks. Once they get to be three meters long, great whites have strong enough jaws to go after heftier prey like marine mammals, including seals, seal lions, and cetaceans. Great whites often ambush their prey, from below, travelling at speeds of 40 km/hr, which means these sharks often leave the water in spectacular bursts of ferocity. Breaches can be more than 3 m in the air, and are most often employed against fur seals in South Africa.
While great whites have a reputation as fearsome man-eating sharks, they actually don’t really like human flesh that much, as we are too bony and not fat enough. Great whites have attacked the most humans of any shark species, though most of these attacks are just test bites, where the sharks take a nice chomp to see if people are worth eating. So reassuring to know that a four meter long shark is biting you just to do a taste test.
The only natural predator of great whites is the killer whale, which have killed great whites in a few notable incidents. Human hunting of great whites also occurs, and though global populations are not known, the species is listed as vulnerable thanks their low reproductive rate. As scary as seeing a great white in the water would be, I can’t deny that these magnificent predators are beautiful, majestic creatures. I’ll just stay in the boat, and everything will be fine. Right?
Cover image credit: Terry Goss via Wikipedia