Shark Read online

  Dampier epitomised the spirit of the age. Modestly educated, he was determined to seek out new information, which he did in abundance, recording important details about the oceans, weather, winds, animals, plants and peoples he encountered. He discovered and explored parts of Australia and he named Shark Bay in Western Australia, his ship Roebuck anchoring there for a week in 1699 while the crew searched the shore for provisions. His journal entries record a variety of fish, birds and mammals, including the sharks that gave the bay its name. Here is his description of a tiger shark (to him, an unknown new world shark):

  ’Twas the 7th of Aug. when we came into Shark’s Bay; in which we anchor’d at 3 several Places . . . Of the Sharks we caught a great many, which our Men eat very savourily. Among them we caught one which was 11 Foot long. The Space between its 2 Eyes was 20 inches, and 18 Inches from one Corner of his mouth to the other. Its Maw was like a Leather Sack, very thick, and so tough that a sharp Knife should scarce cut it: In which we found the Head and Bones of a Hippopotomus [dugong]; the hairy Lips of which were still sound and not putrified, and the Jaw was also firm, out of which we pluckt a great many Teeth, 2 of them 8 Inches long, and as big as a Man’s Thumb, small at one End, and a little crooked; the rest not above half so long. The Maw was full of Jelly, which stank extremely: However I saved for a while the Teeth and the Shark’s Jaw: The Flesh of it was divided among my Men; and they took Care that no Waste should be made of it . . . And thus having ranged about, a considerable time, upon this Coast, without finding any good fresh Water, or any convenient Place to clean the Ship, as I had hop’d for: And it being moreover the heighth of the dry Season, and my Men growing Scorbutick for want of Refreshments, so that I had little incouragement to search further; I resolved to leave this Coast, and accordingly in the beginning of September set sail towards Timor.22

  As quickly as European explorers travelled around the globe, the newly discovered species were exploited for commercial gain: the shark, for example, morphed from sea monster to Enlightenment fashion accoutrement. Commercial competition between the Dutch and British East India Companies, both vying for the spices and woods of the fabled Orient, led to an increased European interest in the East. In 1661, a Dutch newspaper, the Hollantsche Mercurius, reported that 900 ray-skins had been imported by the Company for the Amsterdam Chamber of Commerce. Cured shark and ray skin was called shagreen (from the Persian saghar, the cured hide of a horse or donkey) and had been known in Europe for almost a century. The Musée de l’Armée in Paris holds a Polish Hussar’s sabre with a shagreen-covered hilt which has been dated to 1559. England and France became centres for the manufacture of shark- and rayskin-covered products, which remained popular until the nineteenth century. A craze developed for covering scientific instruments—binoculars, microscopes and the like—with shagreen, as if to link the ‘new’ shark with the explosion of new factual discoveries. Some domestic items were also covered in shagreen, which itself was often dyed green.

  The trade became so profitable that the English manufacturers kept both their sources and species of shark and ray skins closely guarded commercial secrets. In about 1760, a London shagreen casemaker, John Folgham, was advertising his business as:

  Makes & Sells all sorts of Shagreen Nurses, Fish Skin and Mahogany Knife Cases, Shaving & Writing desks, in Mahogany or Fish Skin of different Sorts, Smelling and Dram Bottles & Cases, Canister Cases &c, in Blue or Green Dog skin; Mounted in silver or plain . . .23

  European occupation of the Australian continent also gave rise to many forms of enterprise. In December 1830, George Augustus Robinson recorded in his diary a most unusual fate befalling a group of European sealers, hardy men who worked their trade on the islands of Bass Strait, the unpredictable body of water separating Van Diemen’s Land from mainland Australia. This drama occurred at Clarkes Island reef:

  They had anchored off the reef, but it came on to blow a gale of wind. The sea was running very heavy, but as the seal was going up very fast upon the rocks they kept off, expecting the wind would abate and that they should get a good knock-down. Instead of the wind abating it kept increasing, and the boat parted her cable and went on the rocks and was presently dashed to pieces. They all five got upon the reef, but they had nothing to subsist upon but to kill seal and drink the blood. Two named John Williams and John Brown, finding that the boat did not come to their assistance from Penguin Island, constructed a canoe of seal skins by sewing them together. These rocks are about five miles from Clarkes Island and about the same distance from Penguin Island, and there is an exceeding bad tide rip, equal to the potboil off the Capisheens. They finished their canoe and next morning put to sea, John Williams, who it appears was a great reprobate, saying with a dreadful oath that was the last drop of seal’s blood he would drink on that rock. The men on the reef saw them drifting away with the tide and at last entered a rip, and they never saw them more. They was probably swamped in the rip; or their canoe may have been eaten by sharks, for Parish said that some men on the Hunter [island] covered the frame of a whaleboat with the skins of seals, and was crossing to the other island when the boat was attacked by sharks, and they would soon have eaten through the seams and the whole of them must have perished, but it happened they had some carcases of wallaby kangaroo on board and they kept feeding them until they got over. It is an awful circumstance that Williams and Brown should die in their sins like this. These men had warnings sufficient to make them abandon their wicked course of living, but all the warning in the world is of no use if the grace of God does not reach their heart.24

  For many, the 300-year Scientific Revolution culminated in the 1859 publication of Charles Darwin’s The Origin of Species, so this commentary on sharks is included, although it constitutes a peculiarly bizarre and surprisingly unscientific observation. He wrote in his journal, while on HMS Beagle:

  One day I was amused by watching the habits of the Diodon antennatus [porcupine pufferfish], which was caught swimming near the shore. This fish, with its flabby skin, is well known to possess the singular power of distending itself into a nearly spherical form . . . This Diodon possessed several means of defence. It could give a severe bite, and could eject water from its mouth to some distance, at the same time making a curious noise by the movement of its jaws. By the inflation of its body, the papillae, with which the skin is covered, become erect and pointed. But the most curious circumstance is, that it secretes from the skin of its belly, when handled, a most beautiful carmine-red fibrous matter, which stains ivory and paper in so permanent a manner that the tint is retained with all its brightness to the present day: I am quite ignorant of the nature and use of this secretion. I have heard from Dr. Allan of Forres, that he has frequently found a Diodon, floating alive and distended, in the stomach of the shark, and that on several occasions he has known it eat its way, not only through the coats of the stomach, but through the sides of the monster, which has thus been killed. Who would ever have imagined that a little soft fish could have destroyed the great and savage shark?25

  4

  FATHOMING THE SHARK

  Evolution, Classification

  It shows that Steve came over the top of the ray and the tail came up, and spiked him here [in the chest], and he pulled it out and the next minute he’s gone. That was it. The cameraman had to shut down.1

  This was how a close friend of naturalist and adventurer Steve Irwin, known to the world as Australia’s ‘Crocodile Hunter’, described the camera footage of Irwin’s death on 4 September 2006. Irwin had been making a television documentary about dangerous sea creatures and was snorkelling off the far north Queensland coast when he was killed by a large stingray. His international profile and dramatic death ensured massive media coverage, garnering spontaneous tributes from popstars, politicians and members of the public alike. Irwin’s death is the sort likely to pass into folklore, or myth, like that of Odysseus, ‘who had passed through countless woes of the sea in his laborious adventures, the grievous Sting-ray slew
with one blow’.2

  Had Irwin died in a car crash, or of a more conventional heart attack, public reaction would surely have been less frenzied. The dramatic and unusual nature of the death made it a huge media story. It certainly was unusual but it was not unnatural. In clear shallow water, Irwin and his cameraman had first followed and then swum alongside a large ray, weighing as much as 100 kilograms. It was probably a cowtail ray (Pastinachus atrus). Irwin swam close enough for the animal to feel threatened and it defended itself instinctively, whipping around to confront the large intruder and, like a scorpion, arcing up its long tail. It then rammed the tail’s poison-coated, 20-centimetre-long barbed spine into his heart. An electrosensitive defence mechanism perfected millions of years ago had locked onto the strong electromagnetic pulses generated by Irwin’s beating heart.

  The ray no doubt then swam on to rejoin its companions and is probably still alive and well. At such a size it has few predators, and rays have been known to live for up to 50 years. It would also soon have grown a new tail spine. Little known is that a stingray spine is a highly modified tooth. Equally little known is that technically Steve Irwin was attacked and killed by a shark, because rays are described as ‘flattened shark derivatives’3 or, more colloquially, as sharks’ ‘pancake cousins’.4 Both descriptions reflect the rays’ evolutionary divergence away from the classic torpedo (fusiform) shape as they and the skates adapted to life as bottom dwellers, or ‘benthic specialists’.5 Although recent molecular studies have cast doubt on the closeness of the evolutionary relationship, indicating that the batoids may be a separate monophyletic elasmobranch group, they share many characteristics differentiating them from the teleosts.

  Strange as it may seem, shark-shaped sharks are in fact a minority of their biological class, the cartilaginous fishes, being outnumbered in species count by the batoids—the rays and skates. Even stranger is this question: is a shark a fish? The website of an influential European shark conservation organisation asks:

  Shark or Fish? Sharks are commonly termed fish, even though they are only distantly related to the classical (bony) fish. The evolutionary lines of the cartilaginous and bony fish separated about 400 million years ago.6

  A pioneering twentieth-century American shark authority, Harold McCormick, wrote that, ‘there are even leading ichthyologists who do not regard [sharks] as fishes at all but rather as representing a separate and distinct Class of life’.7 Many sharks bear a superficial resemblance to dolphins, which are mammals; and the largest of all is the whale shark, not a very fish-like name. If a shark is not a fish, however, then what is it?

  The origins of sharks, and their fantastically long journey into the twenty-first century—which so threatens them through destructive human activity—is a story that is in equal measure breathtaking and, now, tragic. And because it is a complex story it should begin simply, with some terminology.

  Non-plant marine life is classified as either vertebrate or invertebrate, that is, without or with a backbone. As shown in the table on the next page, there are six classes of marine vertebrates.

  Osteichthyes (ostee-ick-thez) The bony fishes. Most of the 22 000 known species belong to one infraclass, the teleosts.

  Chondrichthyes (kon-drick-thez) The cartilaginous fishes. More than 1200 known species, grouped in two infraclasses: • elasmobranchs (sharks, skates, rays)

  • holocephali (chimaeras)

  Agnathas Two species of jawless fishes, the lamprey and the hagfish

  Mammals Approximately 120 species grouped in several infraclasses: • pinnipeds

  • cetaceans

  • sirenians

  • sea otters

  • polar bears, generally grouped with marine mammals

  Reptiles Approximately 45 known species grouped in several infraclasses: • sea turtles

  • iguanas

  • snakes

  • crocodilians

  Birds Many thousands of species, including cormorants, gulls, albatrosses, terns, shearwaters, guillemots, puffins and penguins

  There are significant differences between elasmobranchs and teleosts. What they do have in common, apart from their shared liquid environment, is this broad definition of a fish: ‘a poikilothermic [varying body temperature], aquatic chordate [backbone] with appendages (when present) developed as fins, whose chief respiratory organs are gills and whose body is usually covered with scales . . . or more simply, a fish is an aquatic vertebrate with gills and with limbs in the shape of fins’.8

  What they don’t have in common is the result of hundreds of millions of years of unrelated evolution:

  Sharks mate, resulting in the production of relatively few large, hard-cased eggs or live young after a gestation period of at least nine months and up to two years. A female teleost ejects many thousands of tiny eggs into the water which are fertilised when the male ejects his sperm among the eggs. Hatching periods range from less than a week to several months.

  Sharks take up to 20 years to mature and become sexually active. Many teleost species mature in less than two years.

  A shark’s skeleton consists mainly of cartilage. A teleost’s skeleton consists mainly of bone.

  A shark’s liver is large and oil-filled, to provide buoyancy. A teleost has an air-filled swim bladder to provide buoyancy.

  A shark’s gills are uncovered. A teleost’s gills are covered by a moveable, bony plate, the operculum.

  A shark’s skin is covered with modified teeth called dermal denticles, which poke through the skin and are then ‘nonliving’, that is, fixed in size and shape. A teleost’s skin is covered with living scales, which grow as part of the skin.

  Many shark species are solitary. Most teleost species shoal.

  Most shark species have large mouths, containing dozens or hundreds of teeth, which are shed regularly individually or in sets and immediately replaced. Most teleost species have proportionally smaller mouths and fewer teeth, which are anchored individually in the jaw and not replaced as a set.

  A shark’s upper jaw is not fused to its cranium.

  Sharks regulate the amount of salt in their bodies by retaining high concentrations of urea in their blood. Teleosts excrete their urea.

  Sharks total less than five per cent of all fish species and are much longer lived than teleosts.

  Furthermore, while there are tiny sharks and tiny teleosts, there are many shark species that grow far larger than any teleost. The largest teleost, the sunfish, at over four metres and over 2000 kilograms, is dwarfed by its chondrichthyes equivalent, the whale shark, growing to at least 12 metres and weighing 15 000 kilograms.

  Why such major differences? Although elasmobranchs and teleosts have travelled along widely divergent evolutionary paths, both journeys took place in a common environment, our planet’s oceans, seas, rivers and lakes. Oceanographer Meredith Grant Gross has observed that with 70.8 per cent of the planet submerged, ‘ocean is a thin film of water on a nearly smooth globe, interrupted here and there by continents’.9 Approximately 60 per cent of the northern hemisphere is submerged, and 80 per cent of the southern hemisphere. Earth’s longest mountain range is not the Himalayas but the submerged Mid-Atlantic Ridge which extends from north-east of Greenland to Bouvet Island just above Antarctica. Likewise, Earth’s highest mountain is not Mount Everest but Hawaii’s undersea Mauna Kea.

  The average ocean depth is 3800 metres, while the average land elevation is just 840 metres. The maximum ocean depth is recorded at over 11 000 metres, in the Mariana Trench southwest of the Pacific island of Guam; by comparison Mount Everest’s peak is 8850 metres above sea level. The Atlantic is a ‘shallow’ ocean, the Pacific a very deep ocean.

  Oceans have depth layers. The surface or epipelagic zone is defined as being to a depth of about 200 metres and comprises just two per cent of the total body of oceanic water. It is also called the ‘mixed’ layer, as it is subject to atmospheric influences such as rainfall, evaporation, temperature variation and wind. The pycnocline or me
sopelagic zone (the original ‘twilight zone’) descends to about 1000 metres. This layer of denser, more stable water separates the volatile surface waters from the remaining 75 per cent of ocean water, the deep zone. This zone has its own layers: bathypelagic (to 4000 metres, also known as the midnight zone); abyssopelagic (to 6000 metres); hadalpelagic (ocean trenches).

  How did this water originate? There are at least three theories. In the wet-accretion hypothesis, Earth developed from silicate rocks with water trapped inside them. Endless volcanic eruptions turned this water into vapour, creating a dynamic moisture-laden atmosphere. As the planet cooled, this vapour turned into rain which, over millions of years, filled up the gigantic basins that became the three oceans and their smaller seas.

  The late-veneer theory looks back nearly five billion years, when a vast disc of gas, dust and ice began to form into what became our solar system. The proto-system’s rotation and energy formed comets at its outer edge. Millions upon millions of those comets, composed of almost equal proportions of ice and solids, were subsequently drawn back into the inner solar system and bombarded Earth. The young planet’s warmth melted the ice and gravity retained it as water. But this theory suffers from the fact that there is a chemical difference between the hydrogen in Earth water and cometary water.

  A third theory hypothesises a single violent encounter between Earth and a vast, water-carrying embryonic planet, a bit like a water-filled balloon. Recent research suggests that no more than 50 and as little as fifteen per cent of our planet’s water originated from space.10 Less than three per cent of that water is fresh, mostly in the form of ice. Lakes, rivers, groundwater and atmospheric liquid make up just 0.5 per cent of Earth’s water.