与鲨共舞-观鲨潜水-潜水爱好者学习鲨鱼知识的好资料.ppt

* 与鲨共舞 Sharks: We’re not just talking great whites Dive for Sharks There are around 500 known species of shark. Sharks: Large and small Dive for Sharks The whale shark is more than 10m in length – as long as a bus. The spined pygmy shark is less than 25cm long – the size of a shoe. Sharks: Large and small Dive for Sharks Half of all known shark species are less than 1 metre long. Around 80% are smaller than a man. How dangerous are sharks? The answer may surprise you... Dive for Sharks Each year, hundreds of millions of us dive and swim with sharks Although accidents do happen, they are few and far between. No sharks – not even the great white – see us as prey. More humans are killed by dogs, deer and even bees than by sharks. Sharks: Their role in the oceans’ ecosystems Dive for Sharks They have a vital role in mantaining the balance of marine ecosystems. They hunt older, weaker and sick prey – so keep the prey populations in good condition. Most sharks are like lions and wolves of the seas: they are the top predators. Sharks in the Med An amazing variety... Dive for Sharks Mediterranean waters hold over 40 species of sharks, of which 20 are considered top predators. Have you ever seen a shark in the Med? Unlikely Dive for Sharks 18% are at risk of becoming so 26% no data available 42% are threatened with extinction 14% are of least concern The Mediterranean has the highest percentage of threatened shark and rays in the world. Overfishing and accidental catches are the main cause of decline. Have you ever seen a shark in the Med? Unlikely Dive for Sharks The Mediterranean has lost much of its predator diversity. Five of Mediterranean’s top predators – blue, thresher, hammerhead, mako, porbeagle – have declined by 97% in the last 150-200 years. The depletion of large sharks results in changes in the food web. These are serious changes which will have consequences on all animal life – including Man. Shark fishing: The world and EU situation Dive