The encyclopedia of sharks examines in a realistic way the life and biology of these marine predators that first lived in our oceans more than 400 million years ago. Written in a lively style, The encyclopedia of sharks documents every aspect of these beautiful animals: the myths and legends that surround them, the threat that we as humans pose to them, and how they have evolved. Their anatomy and physiology, reproduction, courtship and mating, what they eat, and how they use their extraordinary senses to hunt and survive is also detailed. Specially commissioned charts, maps, illustrations and diagrams accompany the authoritative text, and spectacular photography provides a feast of images. The encyclopedia of sharks will inform, educate, and amaze readers as they begin to understand these awesome animals.
Les informations fournies dans la section « Synopsis » peuvent faire référence à une autre édition de ce titre.
Steve Parker worked at the Natural History Museum in London, England, before becoming an author of more than 100 books. He regularly appears on radio and television.
Jane Parker worked at the Zoological Society of London and then became involved in medical research and genetic engineering. She has written books on subjects ranging from insects to ancient Egypt.Excerpt. © Reprinted by permission. All rights reserved. :
SAVE THE SHARKS
The best place to study sharks is among them, in their natural marine habitat. Advances in diving gear and techniques, hand-held and remote camera technology, recording, tagging systems, satellite tracking, ROVs (underwater remote-operated vehicles) and other fields make studying sharks increasingly rewarding and productive.
Gradually, we can watch sharks in ever more detail and get closer to understanding what makes them tick. One of the first people to attempt serious underwater studies of sharks was the late Jacques Yves Cousteau (1910-1997). With his teams of underwater photographers, film-makers, explorers and scientists, he carried out much original research in the 1950s and 1960s. Cousteau helped to design the first scuba (self-contained underwater breathing apparatus) equipment and pioneered the use of shark cages for observation and filming.
Shark's eye view
The "crittercam" instruments are worn by wild animals for a time then retrieved. Consisting of video cameras and other information-gathering equipment, they are used on various land and ocean creatures. The "crittercam" is attached to the temporarily captured or securely held shark. When the shark is released, the camera records what it sees and where it goes. After a set time the camera strap disintegrates or unlinks, and the camera then floats to the surface, emits a radio signal and is recovered. Research around Australia, North America and South Africa is revealing the behavior of species such as great whites, tiger sharks and bull sharks.
Shark tags vary from simple plastic clip-on versions, usually attached to a fin, to sophisticated tracking devices that emit radio signals and can be detected by boats or even satellites. Some of these radio emitters are safely "force-fed" into the shark, allowing researchers to follow it for several days, until nature takes its course and the device is expelled.
In the northwest Atlantic's Cooperative Shark Tagging Program, scientists, sports anglers and commercial fishing boats work together. They do not bring their catches back but measure the shark, fit it with a numbered tag, then let it go. If it is recaught in a different place, the distance and direction it has traveled and the amount it has grown are recorded. The tags have revealed that some sharks, such as the sandbar shark, mature very late and have few offspring. The conclusion is that when a population is fished out, it will take a long time to recover.
Threats to Sharks
Estimates of the numbers of sharks killed by human activity each year vary from around 50 million to more than 100 million -- that's three dead sharks every second. It compares to around 8-12 human fatalities annually in the other direction.
The threats to sharks vary hugely, as they do with many wild creatures in their natural environments. A great challenge is that we can be presented with eye-catching images of logged devastated rainforests, drained cracked wetlands and oil-polluted shorelines to raise awareness and gain momentum for conservation. But because of visual limits, we cannot encapsulate the threats to the undersea habitat into such telling images.
A great threat to most sharks is the fishing industry and overfishing in general. Some fishing deliberately targets sharks, from hammerheads to dogfish, by various means such as curtain nets, trawls and hooked lines. The sharks are caught for their flesh, liver, oil and other products. One of the most controversial practices is finning (see panel on facing page).
Another problem is bycatch, where sharks are caught incidentally while targeting other fish. Large predatory sharks naturally congregate around schools of prey fish -- and these are also being sought by fishing fleets. The vast nets indiscriminately catch them all. Trapped sharks may be released, but by then they are often fatally injured.
Today's industrialized fishing fleets are so efficient that fish stocks of dozens of species are falling around the world, and some regions are almost fished out. Sharks depend on these types of fish as their food. As the fish disappear, the sharks go hungry and are less likely to grow and breed. Also, as traditionally caught food species of fish become more scarce, commercial fishing turns increasingly to sharks.
Pollution and angling
Some sharks prefer inshore waters, often around bays and estuaries. These are the places where pollution builds up, with sewage, waste and agricultural and industrial chemicals washed into the sea from rivers or inshore effluent pipes. The chemicals enter the food chains, and as smaller fish are eaten by bigger fish these chemicals become more and more concentrated in their bodies, a process known as bioamplification. Sharks are often among the top predators of their habitat and accumulate the highest levels.
Sports angling has also been a threat to the large, desirable sharks such as makos, which put up a spectacular fight when hooked.
Strategies for Conservation
Conservation campaigns picturing attractive and "cuddly" creatures, such as dolphins, pandas, baby seals, and even lion cubs, are designed to arouse public sympathy and support.
A similar campaign using the image of a fearsome shark may be less likely to succeed, but the principles are equivalent. All animals should command our respect as fellow inhabitants of our planet.
Improving the shark's image
Conservation depends heavily on education. A few species of sharks are known to attack humans, true. The same can be said of the tiger -- yet there is widespread global support for tiger conservation.
Responsible education of young people at schools and colleges can obviously help, especially in nature, biology and wildlife topics. Television, books, magazines and websites can also inform about the shark's fascinating behavior and lifestyle.
Safely behind glass
Modern aquaria and sea-life centers contribute enormously to public awareness of aquatic life. Spectacular exhibits in giant tanks with walk-through tunnels allow people to stand inches away from one of the most deeply feared creatures. Most tanks feature a variety of sharks, but particularly sand tiger and sandbar sharks, which seem to take well to captivity yet look sufficiently big and frightening. Accompanying displays, commentaries and videotapes explain shark bodies and behavior.
The shark show
Shark shows truly bring education alive. At the reef, the sharks learn by simple association and habituation that the noise of the boat engine and the splash of people means food. Tourists marvel and take photographs as guards feed the sharks. Such demonstrations can certainly help to change the shark's image, but they depend on a thorough understanding of shark behavior, and there are potential problems. The general wildlife of the reef is disrupted and more sharks may be attracted to the area, which is often near a popular beach resort. It has been suggested that local sharks could even lose their own natural fear of us and come to associate humans with food.
National and international efforts
National governments, regional organizations and international authorities can be persuaded to look after the welfare of marine life and develop strategies for conservation. There is huge potential for fishing quotas and restrictions, which would not only help save sharks but also safeguard almost exhausted stocks of fished-out commercial species. However, many cultural differences remain, such as the popularity of shark's fin soup in certain regions.
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