Doug Perrine Sharks (World Life Library)

ISBN 13: 9780896582705

Sharks (World Life Library)

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9780896582705: Sharks (World Life Library)

This top-selling series introduces readers to the wild creatures of the world and has been expanded to include the wonders of the natural world, too.

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About the Author:

Based in Italy but working around the globe, Andrea and Antonella Ferrari have been professional nature photographers for more than fifteen years. During the past decade they have devoted themselves almost exclusively to underwater photography in tropical seas. They are the authors of four books of photographs and their work has appeared in many newspapers and magazines.

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Lords of the Deep

A New Image

Even today the very word "shark" provokes in us obscure fears and ancestral terrors; and the same irrational sense of danger is evoked by other creatures that are entirely different, such as snakes and wolves, although usually people who react violently and fearfully at the mere mention of these creatures have never seen them in the wild, nor are they ever likely to do so. Actually, the image of these animals, which so inexplicably chills us to the depths of our being, is little more than fantasy, a figment of the imagination derived from decades of bad adventure films, cheap fiction and tall tales unconnected to everyday reality. From the 1930s and 1940s onward, truth and fantasy have overlapped inextricably; first with the discovery and subsequent documentation, usually sensationalized, of tropical shores that had thus far remained unviolated, and then with incidents arising from the Second World War. So, although it was obviously impossible for anyone to rip open a shark with a single thrust of a knife, as was done repeatedly in the cinema, it was nonetheless tragically true that many torpedoed sailors and bailed-out pilots -- who during the war had been left at the mercy of the sea, often for days on end -- had been killed by these predators while awaiting the arrival of help.

It is undeniable that certain species of tropical sharks -- and also other huge predators such as the Nile and marine crocodiles -- have long represented a genuine danger to people living along river banks. What, however, is important to grasp is that such sharks, stripped of the cloak of myth and superstition in which they have been wrapped by innumerable travelers and writers, are merely fish. Often of extraordinary elegance and beauty, sometimes astonishingly evolved, in some cases capable of inflicting grave wounds with their spectacular teeth, yet, at the same time simply fish, unable to show human-type feelings such as malice or desire for revenge, instinctively prepared to flee if threatened, tending to be timid and difficult to approach, and often surprisingly delicate. Today, as is evident, it is actually sharks that have reason to fear humans, not the other way round.

Similarities and Differences

In what way do sharks differ from other fish? Sharks and rays are cartilaginous fishes, the Chondrichthyes, of which they form the subclass Elasmobranchii, in contrast to the Osteichthyes or bony fishes. Like the latter, they extract the oxygen necessary for life from the surrounding water by a specialized structure of the gills, and they move by undulating the streamlined body using a combination of fins, either single (caudal, dorsal and anal) or paired (pectoral and pelvic). Many of them are carnivorous hunters, and they reproduce, depending on species, either by laying eggs or producing live young. The structural features that distinguish the Chondrichthyes are the gills (which in sharks open on the outside as simple slits, varying in number from five to seven, whereas in bony fishes they are always protected by a bony covering known as the operculum); the fins (stiff and laminate, similar to the wings of an airplane, without bony inner rays that characterize the Osteichthyes); the skin (which in sharks consists of a layer, of variable thickness, of derma in which are embedded innumerable enameled tooth-like placoid scales, whereas in bony fishes they generally take the form of large, flat scales); and finally and most particularly, the skeleton, which is made up mainly of strong cartilage rather than hard bone as is the case with Osteichthyes. Sharks, moreover, have no swim bladder and the majority regulate their balance in water through their highly evolved body structure and the large size of their liver, which is rich in oils. Another important distinction between the Chondrichthyes and the Osteichthyes is the general structure of the upper jaw or maxilla (as opposed to the lower jaw or mandible) which in practice is not fused to the skull. Sometimes this arrangement results in a spectacular projection of the teeth -- so conspicuous in books and films devoted to the great white shark, Carcharodon carcharias -- enabling such species to rip huge chunks of flesh from their prey.

An Incredible Variety

In other respects it is impossible to generalize. Some sharks are under 15 cm (6 in) long and others grow to more than 15 m (50 ft); yet about half of the existing 400 or so currently classified species measure less than a meter in length. Certain species are notable for their exceptional predatory capacities (tiger shark, mako, white shark, hammerhead); others feed exclusively on microscopic organisms in the form of plankton. About twenty-five species are known to have deliberately attacked humans on many occasions, but the number of attacks recorded each year throughout the world is generally less than a hundred. The most dangerous species for swimmers is probably the bull shark, Carcharhinus leucas, also known as the cub shark. For skin-divers, however, the most perilous species -- according to the celebrated underwater explorer and author, the late Jacques-Yves Cousteau -- is the oceanic whitetip shark, Carcharhinus longimanus. Many species, nevertheless, may turn extremely dangerous if triggered off by the phenomenon of "feeding frenzy" (typical also of tuna), during which individuals launch furious, repeated attacks on prey such as a shoal of fish). On such occasions they are likely to attack whatever comes within their reach, including other sharks, which are sometimes wounded and devoured.

A Perfect Animal

Popular culture has it that sharks are primitive and stupid, but nothing could be further from the truth. Under normal conditions, sharks behave with quite a measure of intelligence, and various experiments have shown that their learning capacity compares with that of rats and birds. Moreover, the fact that present-day sharks, which exhibit an astonishing range of diversity, have not changed substantially for the last 150 million years (with the oldest going back 350 million years) suggests they have attained a level of evolution that approaches perfection. They are consummate predators (equipped with as many as 3,000 teeth, arranged in five rows); incomparable swimmers (the blue shark, Prionace glauca, migrates annually more than 3,000 km (1,860 miles) following the Gulf Stream, while the mako shark (Isurus) may reach a speed of 35 kmh (21 mph); and highly prolific breeders: the female blue shark may give birth to as many as 135 young.

Sharks are exceptionally adaptable animals that have come to occupy many ecological niches, from tropical seas to the Arctic and Antarctic oceans, and are sometimes present in freshwater streams and rivers. Species may be pelagic or coastal, migratory or sedentary, midwater or benthic. However, like other highly developed animals, they have to adjust progressively to biological change (a long growth period and late sexual maturity) and hence need time to adapt to altered environmental conditions. Human modification of the earth's habitats at an astonishing rate is threatening the extinction of many species. During the last ten years alone humans have done more harm to present-day sharks than had been done in the 150 million years since they first appeared. Throughout their long history, sharks, which survived the age of the dinosaurs unscathed, have never faced such a grave threat to their future existence.

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