字幕表 動画を再生する 英語字幕をプリント Here are some facts about great white sharks: white sharks are live-birthed, usually in litters of between four and seven individuals. Now they're called pups, but when they're born they're between 1.2 and 1.5 meters! So that's a pretty big baby. It takes a great white shark about ten to twelve years to reach maturity at which point the females are actually about a meter longer than the males - the largest recorded being over six meters - roughly the size of this red boat behind me. At this length they'd weigh about two to three thousand kilograms. Oh man! Now there are stories of some great whites being over seven meters but those are unsubstantiated. White sharks are warm bodied. They're not warm-blooded like us - they can't maintain a perfectly stable temperature, but their internal organs are kept at up to thirteen degrees above the average temperature of the ambient water around them. The heat generated by their muscles is actually transferred to the blood in their veins as it returns from the shark's extremities, so it warms it up and keeps the core temperature a little bit hotter. This allows the shark to venture into colder waters and also to have explosive power. Its muscles work a lot better when warm than when cold, just like ours. The tradeoff is the shark requires about ten times as much energy as if it didn't heat its body and that's why they need to feed on these blubber-rich seals and whale carcasses. White sharks like to hunt when it's light out because they use their eyesight to spot their prey. But when they open their jaws, their eyes actually roll back into their head to protect them and so they're actually blind when they're taking a bite. Now they do like conditions that are a little low visibility because they rely on stealth to track down their prey. If a seal spots them coming, it's basically game over because the seal is so much more maneuverable and it can definitely get away from the shark. But they only eat sea mammals after they're about 2.5 meters long, which is why most of the sharks we're seeing around here are quite large. Before that, they're diet consists mainly of fish. The gestation period is thought to be about eighteen months and that leads to a two to three year reproduction cycle and with such small litters that means it takes a long time for this shark population to recover. There are a couple misconceptions about great white sharks. One is that they can't get cancer and that's led to a lot of people hunting them down and trying to use their fins as an anti-cancer soup. But in reality sharks get cancer just like anything else and there is photographic evidence of sharks with big tumors so it makes no sense to hunt down sharks as a cancer remedy because they get cancer just like we do. Another misconception is sharks are coastal creatures that just cruise the beaches waiting to bite people. In reality the sharks spend much of their time way, way out at sea and very deep, over a kilometer deep. It's kind of shocking but we've only found this out in the last couple of years so there is so much about sharks that remains undiscovered. We don't know where they go or what they do for most of the time that they're alive. That's why research projects like this are so important to find out more about the shark and figure out how we can help it rehabilitate and become the predator of the sea that it once was.