Handy Pocket Guide to Tropical Coral Reef Fishes. Gerald Allen

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      Introduction

      Fishes are by far the most abundant group of vertebrates—approximately 24,000 species inhabit fresh and marine waters. They are also the oldest backboned animals, having evolved in ancient seas nearly 500 million years ago. An incredible variety of habitats are populated by fishes—virtually every conceivable aquatic environment, from deep ocean trenches to high alpine streams. The group is so diverse it is difficult to define them, but most breathe by means of gills, have a protective layer of scales, and propel themselves through water (a medium that is 800 times denser than air) by means of fins. However, there are numerous exceptions—eels, for example, usually lack scales and have either much reduced fins or none at all.

      Warm, clear seas of the Indo-Pacific, the vast region stretching between East Africa and the islands of Polynesia, have nurtured the development of nature's richest realm—the living coral reef. This region, centred on the Indonesian-Philippine Archipelago, is the world's most extraordinary biological province. Nowhere else can one find such a wealth of colourful and diverse marine life. More than half of the world's total fishes are found in this region. They range in size from the gargantuan, 12-metre-long Whale shark to diminutive gobies that are smaller than one's fingernail.

      Except for a relatively small number of locally or regionally restricted species, known as endemics, most fishes in the Indo-Pacific have broad distributions—in many cases ranging all the way from Africa to Polynesia. Their broad dispersal is the result of the pelagic larval stage common to most reef fishes, in which the tiny young are propelled through surface waters by winds, waves and currents. The end result is a closely interrelated community of fishes inhabiting the length and breadth of the Indo-Pacific region. This is clearly an advantage for anyone wishing to learn the fishes of different localities within this vast area. Nearly all families, most genera and many species will be the same regardless of whether you are at Tahiti, Indonesia or the Maldive Islands.

      The tremendous abundance of fishes seen during a single scuba dive or snorkeling session may seem staggering. Indeed, in some areas one can find as many as 300 species inhabiting only one or two hectares of reef. But there is no need to despair. This Periplus Nature Guide is an excellent introduction to the reef's most commonly encountered species. The entries are grouped according to family, and arranged in conventional taxonomic order. An index which includes both common and scientific names can be found at the end of the book. Fish watching is the aquatic counterpart of bird and butterfly watching. Almost anyone can enjoy this enriching hobby. The only essential equipment is a mask and snorkel, although of swim fins are also a good investment. Every fish that you encounter has an interesting story to tell about its unique habits and special way of life.

      Leopard Shark

      Stegostoma fasciatum

      Family: Stegostomatidae

      The Leopard shark is distinguished by a whisker or "barbel" at each corner of the mouth, prominent ridges on the side of the body and a huge tail, which makes up about one-half of its total length. Adults, which grow to more than 300 cm, have a distinctive pattern of leopard-like spots. Another common name for this species is Zebra shark, based on the juvenile pattern—primarily black with vertical white bands. Of all the sharks in the tropical Indo-Pacific region it is among the easiest to identify due to its colour, shape and habit of resting on the bottom. It feeds mainly on gastropod and bivalve molluscs, but crustaceans (crabs and prawns) and small fishes are also eaten. There is very little information about its behaviour, other than its habit of lying on the bottom for long periods. Females are known to deposit several large (approximately 8 x 17 cm), blackish egg cases. There are no reports of human attacks by this species. It pays little attention to divers or flees at their approach.

      Blacktip Reef Shark

      Carcharhinus melanopterus

      Family: Carcharhinidae

      This is one of the most commonly seen sharks in the Indo-Pacific region. It prefers shallow water close to shore, often on reef flats as shallow as 30 cm. Maturity occurs at a size of about 100 cm and the maximum length is about 170 cm. The young, which are born alive, measure between 33 and 52 cm. The Blacktip is an active, strong-swimming shark that occurs singly or in small groups. The diet consists mainly of small fish, cephalopods and shrimps. While not considered a dangerous shark, it has attacked humans. Most attacks appear to be cases of "mistaken identity"—instinctively homing in on the wader's splashes and mistaking the disturbance for struggling fish. The species is commonly seen in public aquaria.

      In the 1960s, the author sent the first live shipment of young Blacktips to the Steinhart Aquarium in California. The sharks were captured by hand at low tide on the reef flat at Enewetak Atoll in the central Pacific.

      Silvertip Shark

      Carcharhinus albimarginatus

      Family: Charcharhinidae

      This sleek predator is common in clear water, particularly on steep slopes, below depths of 20-30 metres. The geographic range extends from East Africa and the Red Sea to the Pacific coast of Central America. It is a dangerous species that is known to attack humans. It has the habit of passing uncomfortably close to divers should they enter its territory. Its normal food consists of a variety of fishes, including wahoo, eagle rays, wrasses and tunas. It will also consume octopuses and squids.

      This shark should not be confused with the Reef whitetip, a harmless, relatively sluggish species that is often seen in shallow water. Both sharks have similar white markings on the dorsal and caudal fin, but the Whitetip is more slender and lacks white on the pectoral fin tips. The maximum size of the Silvertip is about 200 cm. The young, which measure between 63 and 68 cm, are born alive. Each litter contains 5 or 6 babies, but there may be as many as 11.

      Scalloped Hammerhead Shark

      Sphyrna lewini

      Family: Sphyrnidae

      The odd head shape typical of this family of sharks has been the subject of considerable speculation. Scientists believe it serves a twofold purpose of increasing manoeuvrability and enhancing sensory capabilities. The uniquely flattened head acts as a bowplane, allowing it to move swiftly through the water. The expanded surface area along the front of the "hammer" is crammed with special sensory cells for detecting pressure changes and electromagnetic fields, not unlike the sensor plate of a metal detector. In addition, the widely-spaced eyes may enhance their binocular vision.

      The family contains nine species, of which the Scalloped hammerhead is one of the most common and widely distributed. It occurs in all tropical and warm-temperate seas. They sometimes congregate over sea mounts or around offshore islands, forming schools of hundreds of individuals. This shark is potentially dangerous, but attacks are rare. Maximum СКАЧАТЬ