Unit_13_swimming with sharks_培训课件.pptVIP

Unit: 13 Swimming with Sharks Sharks Sharks are a type of fish with a full skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago. Since that time, sharks have been divided into 440 species, ranging in size from 17 cm in length, to the whale shark, the largest fish, which reaches about 12 meters. Sharks are found in all seas and are common down to depths of 2,000 meters. They generally do not live in freshwater, with a few exceptions such as the bull shark and the river shark which can live both in seawater and freshwater. They breathe through five to seven gill slits（鳃裂）. Sharks have a covering of dermal denticles（肤齿） that protects their skin from damage and parasites, and improves their fluid dynamics so the shark can move faster. They have several sets of replaceable teeth. Shark tourism Shark tourism is a form of eco-tourism rooted in having communities appreciate that local shark species are more valuable alive than dead. Instead of opting for a one time economic benefit of harvesting sharks for their body parts, communities are made to assist interested tourists who may want to see live sharks. Many divers and people are involved in interest groups that aim to celebrate and promote safe and responsible shark diving activities. Great White The Great White Shark, also known as White teeth, is an exceptionally large lamnidae (oceanic shark) found in coastal surface waters in all major oceans. Reaching lengths of about 6 meters and weighing almost 2,000 kg, the great white shark is the world’s largest known predatory fish. Seal Island it is a small land mass located about 5.7 km off the northern beaches of False Bay, near Cape Town, in South Africa. The island is occupied by Cape Fur Seals and a few sea birds. Catch-22 it means an impossible situation that you can not solve because you need to do one thing in order to do a second thing, but you can’t do th