Lamniformes

(Mackerel sharks)

Class Chondrichthyes

Order Lamniformes

Number of families 7

Evolution and systematics

Living lamniform sharks are mere remnants of a much greater lamniform lineage that has, for the most part, become extinct. The 15 surviving species pale in comparison to the countless hundreds that have been described from fossil remains; the genus Carcharodon alone is known from some 10 fossil species, in contrast to the single extant Carcharodon carcharias. However, the overwhelming majority of these fossils consist of isolated teeth, first appearing in the fossil record during the early Cretaceous period some 120 million years ago (mya). Fossil lamniform teeth are known from many widespread marine localities from all continents, and they resemble those of living mackerel sharks in usually being slender, with very sharp cusps and arched roots. Many living lamniform species have closely related fossil relatives, again known only from teeth, going back at least to the Paleocene epoch (some 62 mya). Some of these fossil species are even placed in genera that are still extant (e.g., Carcharodon, Odontaspis), corroborating that lamniform sharks have a remarkably long evolutionary history, as do most living shark groups.

Fossil lamniforms known from more complete remains are extremely rare and include preserved partial skeletons of goblin sharks (Mitsukurinidae) from Lebanon (about 90 million years old), and vertebrae of various taxa, such as the megalodon shark from Europe (of Miocene to Pliocene age, some 16 to 2.6 mya). The late Cretaceous goblin shark (Scapanorhynchus lewisi) is similar to the living goblin species (Mitsukurina owstoni) in having a very elongated snout, but it differs in having a much longer anal fin and more angular dorsal fins. Moreover, some features of its teeth and denticles differ as well. The megalodon shark (Carcharodon megalodon) is the most notorious fossil lamniform. It is known from huge, triangular teeth (as large as 7.9 in [20 cm] in height), that are very similar to teeth of the living white shark (Carcharodon carcharias). The megalodon shark, however, was much larger (estimated to reach up to 49 ft [15m] in length), some three times the size of the living white, and was one of the greatest marine predators of all time (and the greatest macropredatory shark). Reconstructions of its jaws, believed to have been able to fit several people when agape, feature in many museum exhibits. Megalodon fossils are known from North and South America, the Caribbean, Europe, Australasia, Japan, and Africa.

Among living elasmobranchs (sharks and rays), lamniform sharks are more closely related to the ground sharks (Carcharhiniformes), bullhead sharks (Heterodontiformes), and carpet sharks (Orectolobiformes). These four orders, united in the larger group Galeomorphii, share various evolutionary innovations, such as the unique placement of the hyomandibula (a cartilage supporting the jaws posteriorly) on the skull. Within this group, lamniforms are most closely related to the ground sharks, as both orders share a tripodal rostrum supporting the snout internally.

Living lamniforms are among the most intensely studied and best-known sharks. Four of the living species were described in the eighteenth century, five in the nineteenth, and six in the twentieth century. (The last species described was the megamouth shark in 1983.) They are currently divided into seven families, 10 genera, and 15 species, and they were first recognized as a unique group by American ichthyologist David Starr Jordan (1851–1931) in 1923.

Phylogenetic (evolutionary) relationships among lamniform genera also have received much recent attention. The goblin shark (Mitsukurina) is considered the most basal, or primitive, living lamniform, followed by the sand tiger sharks (family Odontaspididae) and the crocodile shark (Pseudocarcharias). The remaining mackerel sharks have plesodic pectoral fin skeletons, in which the internal supports extend to the distal fin margin. Recent phylogenetic theories also support a common ancestry for a lamniform subgroup—comprising the basking shark and lamnids—with lunate caudal fins. Phylogenetic studies based exclusively on characters from the teeth disagree to some extent with those based on

the skeleton, but teeth can often be misleading as indicators of evolutionary relationships in sharks and rays. Molecular phylogenies are also partly at odds with morphological ones, indicating that the evolutionary history of many lamniform genera is still in dispute.

Physical characteristics

Mackerel sharks are moderate to very large, ranging from about 3.3 ft (1 m) to 49 ft (15 m) in length. Some mackerel sharks, such as the great white and shortfin mako, are among the most popularly known and easily recognizable of all sharks. Other mackerel sharks are among the most bizarre and anatomically unique sharks, such as the megamouth, goblin, and thresher sharks. Lamniform sharks have unique teeth and intestines with a ring valve (with numerous, closely stacked turns).

There is some variation among lamniform species in relation to body and fin profiles, but all mackerel sharks have two dorsal fins (usually the first dorsal fin is very tall, while the second is reduced in height), large pectoral fins (except in the goblin and crocodile sharks, and to a lesser degree in the sand tiger sharks), and a small anal fin (except in the goblin and sand tiger sharks). The caudal fin is lunate or semilunate (i.e., with a well developed lower lobe) and upright in some species (basking shark and lamnids). Thresher sharks have caudal fins about equal to the length of the body, and goblin, sand tiger, megamouth, and crocodile sharks have caudal fins with relatively small lower lobes. The snout is conical in most species (except in the megamouth shark), and paddle shaped in the goblin shark; internally the snout is supported by a tripodal rostrum, usually composed of three cartilaginous segments. The spiracles are extremely reduced. The eyes are black and round in most species and lack nictitating (protective) membranes. Five pairs of gill openings are present. Denticles along the body are very small and do not form larger spines.

Some lamniform species, particularly those of the family Lamnidae (white, porbeagle, salmon, and mako sharks) are capable of maintaining slightly elevated body temperatures in relation to the surrounding water. This is accomplished in a manner similar to tunas and mackerels (bony fishes of the family Scombridae), through a counter-current, vascular heat-exchange system. The body musculature, viscera, brains, and eyes remain at temperatures from 5.4°F (3°C) to 25.2°F (14°C) warmer than ambient water. This physiological mechanism enables lamnid mackerel sharks to maintain higher metabolic rates; hence they are capable of great bursts of activity.

Lamniforms are usually blue or blue-gray on their dorsal and lateral sides, but white to off-white ventrally. Well-defined spots and blotches are mostly absent, but the white shark has black ventral pectoral fin extremities, and some species may have whitish blotches on the tail; the salmon shark, Lamna ditropis, has brown blotches on its lateral and ventral aspects.

Distribution

Mackerel sharks are found worldwide in tropical and temperate marine waters. Some species penetrate boreal and subantarctic seas (basking shark and species of the genus Lamna), and other species are extremely wide-ranging, such as the shortfin mako and white shark. All species are somewhat widespread.

Habitat

Mackerel sharks are present in shallow, coastal waters, as well as epipelagically and mesopelagically in deeper oceanic waters. Most species, such as the mako, white, and sand tiger sharks, occur predominantly in shallow areas, while others are demersal inhabitants of continental slope regions (e.g., the goblin shark).

Behavior

The behavior of sharks that inhabit oceanic realms is generally not well known. Lamniform sharks, however, display different behaviors in relation to feeding (from filter feeding to predation), as well as in relation to metabolism. The more active species are laeterothermic (slightly warm-blooded); as a result they can swim at astounding speeds and are capable of great bursts of energy. The filter-feeding species, however, are relatively sluggish. Many species of lamniforms are known to leap completely out of the water (breaching), and not only as a result of being hooked on a line. The reasons behind this behavior are largely unknown but may have to do with escaping predators, snatching prey (as in the white shark), or ridding themselves of parasites. A lunate caudal fin may facilitate the strong upward swimming necessary to breach the water surface. Segregation by sex and size has been recorded in lamniform sharks, but much is yet to be learned about their population dynamics. More specific behavioral patterns have been described for particular species in the species accounts below.

Feeding ecology and diet

Almost all mackerel sharks are predaceous, extremely active eaters, feeding mostly on fishes belonging to numerous families (both bony fishes as well as sharks and rays), but also consuming large amounts of invertebrates (e.g., squids, octopi, gastropods, crustaceans) as well as marine mammals (pinnipeds, dolphins, and whales, as well as whale carcasses), marine turtles, and even oceanic birds. In contrast, two species, the megamouth and basking sharks, feed almost exclusively on zooplankton, and current evolutionary theories indicate that filter feeding evolved independently in both species, which also differ in their mode of filter feeding. Lamniform sharks are preyed upon by other shark species, including their own species.

Reproductive biology

As far as is known, all species of mackerel sharks are yolk-sac viviparous (ovoviviparous, aplacentally viviparous); i.e., they give birth to live young that develop in utero and that feed on the yolk contents of their yolk sacs. But in many lamniform species, intrauterine cannibalism has been confirmed or is suspected. This occurs when embryos prey on each other (adelphophagy) or on other eggs (oophagy) inside the uterus after their yolk reserves are depleted. This group is the only elasmobranch taxon in which this occurs. Adelphophagy is known for certain in only one species, Carcharias taurus, but is suspected in others. Gestation periods vary among species and are comparatively poorly known. In some species, females are gravid from eight months to one year, while other species have longer gestations (up to 18 months). A period of reproductive inactivity may follow a gestation. Courtship patterns are presumably similar to those in many other sharks, with males biting females to subdue them prior to copulation and also during copulation.

Conservation status

The following species are listed by the IUCN: Alopias vulpinus, Lamna ditropis, Megachasma pelagios, and Odontaspis noronhai (as Data Deficient); Carcharodon carcharias, Carcharias taurus, and Cetorhinus maximus (as Vulnerable); Lamna nasus, Isurus oxyrinchus, and Pseudocarcharias kamoharai (as Lower Risk/Near Threatened).

Significance to humans

Many lamniform species are captured on longlines or trawls, either as bycatch or as specific targets, by the commercial fishing industry. The flesh is consumed fresh, frozen, smoked, or dried-salted, and their fins are procured by the destructive shark fin soup industry. Sport fishing for makos and other lamniforms is also common. This order contains what has been considered to be the most dangerous shark species, the white shark. But the misguided, anthropocentric perception that the white shark and other lamniform species are potential "man-eaters" has faded in the past decade; this negative image was given to this species mostly by sensationalistic media. Ironically, the roles are presently reversed, as it is now well understood that it is the sharks that are the victims of humankind, mostly through overfishing and the ruthless, cruel, shark fin soup fad, and not the other way around. In fact, many species of lamniforms and other sharks are quite valuable alive. The sand tiger shark is important as an exhibition fish in public aquaria, where it is relatively easily kept for long periods. Many lamniforms, such as the sand tiger, white, thresher, basking, and mako sharks, are even common ecotourist attractions in many places around the world.

Species accounts

List of Species

Thresher shark

Alopias vulpinus

family

Alopiidae

taxonomy

Squalus vulpinus Bonnaterre, 1788, Mediterranean Sea.

other common names

French: Renard; Spanish: Zorro.

physical characteristics

A very characteristic, large shark that may reach over 19.7 ft (6m) in length, with an extremely elongated caudal fin (as long as the body), prominent first dorsal fin, minute second dorsal and anal fins, long pectoral fins, and small, conical snout. Coloration blue-gray to dark gray dorsally and laterally, with a white abdominal region, and white blotches laterally anterior to tail.

distribution

Circumglobal in both coastal and oceanic, tropical to temperate, waters.

habitat

Usually occurs over the continental shelf region, close to the surface, but also occupying oceanic waters down to a depth of 1,200 ft (366 m). Younger specimens are more commonly found inshore.

behavior

Thresher sharks are swift, vigorous swimmers, capable of breaching. They segregate by sex and migrate seasonally off the western coast of North America.

feeding ecology and diet

Preys mostly on a wide variety of epipelagic, midwater, and demersal fishes, but known to feed also on squid, octopi, pelagic crustaceans, and even seabirds. Uses its long tail to stun prey, entrapping them by swimming in increasingly smaller circles around schools of fishes, sometimes even in tandem with another thresher shark.

reproductive biology

Yolk-sac viviparous, embryos apparently are uterine cannibals (oophagy). Litter numbers range from two to six, most commonly four; three to seven have been recorded in the eastern Atlantic. Young remain for a short period in shallow water nursing grounds. A gestation period of nine months has been reported for California populations, where mating occurs in the summer. Individuals are sexually mature between three and eight years old. Individuals may live for 50 years.

conservation status

Listed as Data Deficient by the IUCN.

significance to humans

Caught by both commercial (mostly with longlines) and recreational fisheries, and consumed (or have been) in somewhat regular quantities in many locations, from almost all major oceans. Heavily fished off the West Coast of the United States in the late 1970s, but because overfishing led to a significant decline in stocks, the targeted fishery was terminated in 1990, though they were still captured as bycatch. Not considered dangerous, but they command respect because of their large size and possible aggressiveness.

Basking shark

Cetorhinus maximus

family

Cetorhinidae

taxonomy

Squalus maximus Gunnerus, 1765, Norway.

other common names

French: Pélerin; Spanish and Portuguese: Peregrino.

physical characteristics

An unmistakable, huge shark, with extremely elongated gill slits (reaching from the dorsal to the ventral side), a very wide gill region when gills are expanded during feeding, a large, capacious mouth, well-developed gillrakers on the inside of the gills to capture small food particles, very small teeth, elongated pectoral fins, and a large lunate caudal fin. Grayish in color all around. Reported to reach 40–50 ft (12.2–15.2 m) in length, but large specimens are more common at about 33 ft (10 m).

distribution

Worldwide in mainly coastal, cold, temperate waters, most abundant off both sides of the northern Atlantic, but also in warmer, subtemperate regions such as the Mediterranean Sea.

habitat

Usually found over relatively shallow, coastal, pelagic waters but can be caught in open seas over deeper waters. Basking sharks appear in regular periods in certain areas (probably to feed) but also disappear in what appears to be regular cycles. Where they "disappear" to is a mystery, and perhaps they "hibernate" or spend periods of relative inactivity on or close to the bottom of the ocean.

behavior

Basking sharks have been seen to leap clear out of the water (as have other mackerel sharks). Usually they are observed cruising at about 2.3 mph (2 knots) near or at the surface, with their mouths open during feeding. They are highly migratory, and several individuals may swim in tandem.

feeding ecology and diet

A filter-feeding shark, capable of taking in massive amounts of zooplankton. It swims with its mouth open very wide, retaining food items on its gillrakers, which are covered by denticles, giving them a rough texture. The gillrakers are shed periodically, usually in the early winter. Basking sharks feed mostly in the summer months near the surface. They either feed by alternative means when the gillrakers are shed, or remain without feeding, inactive, until they are regenerated. Food is retained in the gillrakers, aided by secretions of mucus in the pharynx, and subsequently swallowed when the mouth is closed.

reproductive biology

Basking sharks employ yolk-sac viviparity, giving birth to two to six pups per gestation. The pups are the largest of all shark species, ranging 59–67 in (150–170 cm) in total length. Gestation periods are mostly unknown but are estimated to be very long (more than 1 year). The ovaries produce huge quantities of eggs.

conservation status

Listed as Vulnerable by the IUCN and protected in the United Kingdom, Malta, United States (East Coast), and New Zealand. Protection is pending in other areas (Mediterranean Sea, South Africa).

significance to humans

The basking shark has been captured in much of its range since the nineteenth century for its oily liver, which may contain up to 500 gal (1,893 l), meat (fresh and dried-salted), and skin, and also for its fins for the abhorrent shark fin–soup industry. Populations of the basking shark have declined significantly in many regions. The basking shark has some importance for the tourism trade, as it can be seen in many places, especially in the northern Atlantic (e.g., Bay of Fundy, Cape Cod, Isle of Man). Harmless, this shark poses no direct danger to people, but deserves respect because of its large size.

White shark

Carcharodon carcharias

family

Lamnidae

taxonomy

Squalus carcharias Linnaeus, 1758, Europa.

other common names

English: Great white shark; French: Grand requin blanc; Spanish: Jaquetón blanco.

physical characteristics

Very large, reaching to 21.3 ft (6.5 m), more commonly to 18 ft (5.5 m), with a distinctive dentition comprised of large, triangular teeth with serrations on both edges, and with lateral cusps in embryos. They have a conspicuous white ventral coloration and a gray-to-bluish dorsal and lateral shade (the ventral and dorsal colorations are clearly separated on the sides), large gill slits, well-developed precaudal keels, a large first dorsal fin (much larger than the second), large and lunate caudal fin, pectoral fins with black tips ventrally, a conical snout, and a large, black eye.

distribution

Worldwide in coastal marine waters, and also around oceanic tropical islands, but more common in cold and warm temperate regions, and apparently rare or absent from most of the western Indian Ocean, Indonesia, and tropical Central America. Most common off California, Australia, and South Africa. Compared to other shark species, the white shark is relatively uncommon where it occurs.

habitat

The white shark is primarily a continental shelf inhabitant, cruising through relatively shallow waters either near the surface or close to the bottom. It also is found off oceanic islands and inshore bays and has even been captured on a bottom longline as far down as 4,199 ft (1,280 m). Capable of wide excursions in the pelagic realm.

behavior

Whites are solitary and nomadic, and may occur in pairs, but feeding aggregations of some ten individuals also have been observed. It is known that they will leap completely out of the water (breaching) when capturing surface prey (or perhaps for other reasons). They are even capable of breaching vertically in a manner similar to dolphins. "Spy hopping" (when the shark will maintain its head out of the water as if to search the surroundings) and "repeated aerial gaping" (RAG; when the shark "bites" the air with its head clear out of the water) also have been observed. The white shark is known to satisfy its curiosity by circling intended prey items, or even boats and divers. It is capable of great bursts of speed. While feeding, their eyes roll back in their sockets. There may be segregation of individuals according to size.

feeding ecology and diet

The white shark is a formidable predator, feeding mainly on numerous families of bony fishes (as well as a large variety of sharks, even the basking shark), sea turtles, marine mammals (pinnipeds and whale carcasses), and even sea birds resting on the surface. Invertebrates also may be eaten (such as crabs), but most of its food comes from fishes and marine mammals taken from the surface or in the water column. White sharks are one of the top predators in the ocean; however, they sometimes fall prey to orcas (killer whales).

reproductive biology

Embryos develop inside the uteri (yolk-sac viviparous), and intrauterine cannibalism (oophagy) is confirmed, as embryos have been found to have great amounts of yolk and egg membranes in their stomachs. Teeth also have been found in the stomachs of embryos, but embryos are believed to swallow their own teeth during development, as they undergo tooth replacement several times before birth. Gestation periods are mostly unknown. A litter of nine pups was reported for one pregnant female from the Mediterranean, and up to 10 embryos may reach term (data from gravid Japanese whites). The lack of knowledge concerning their reproduction is due to the scarcity of gravid females, perhaps an indication of pronounced segregation during gestation, or even of low fecundity. Size at maturity for females is between 13.1 ft (4 m) and 16.4 ft (5 m) long, and between 11.5 ft (3.5 m) and 13.1 ft (4 m) for males. Age at maturity ranges from 12 to 14 years for females and nine to 10 for males. Embryos measure 4 ft (1.2 m) to 5 ft (1.5 m) at birth, and can weigh up to 55 lb (25 kg). Courtship has been observed in one instance; the male bit the female into submission preceding a 40-minute-long copulatory embrace.

conservation status

Presently threatened in many locations (e.g., Australia, South Africa) and heavily protected in Australia, South Africa, Namibia, Israel, Malta, and the United States. Australia is apparently the only country in which there is a detailed recovery plan for this species. Whites are listed as Vulnerable by the IUCN.

significance to humans

The white shark is perhaps the most notorious of all sharks, with an undeserved reputation as a "man-eater" and threat to humans. There are attacks on humans attributed to this species every year, but they average only about three per year from 1952 to 1992 (increasing slightly towards 1999). Attacks by the white are rare, however, when the whole phenomenon of "shark attack" is taken into account. About 80% of all shark biting incidents have occurred in the tropics, where whites are far less common than in temperate zones. Attacks by whites are even more insignificant when one considers that more people have died from incidents with domestic livestock (e.g., pigs) than have died of attacks from this shark. Much of the maligned popular image is a result of the Jaws movies. However, it is the white shark that is in dire straits as a result of being slaughtered by recreational and commercial fishermen, either intentionally for trophies or as bycatch. Contrary to its folkloric, Jaws image, the white shark is worth more alive than dead and is an extremely valuable asset to ecotourism in many locations, attracting scores of interested onlookers who pay generously to see the creature from the protection of a submerged cage. Perhaps no other shark inspires as much fear and admiration as the white. A recent symposium volume (Great White Sharks, The Biology of Carcharodon carcharias) summarizes much valuable information concerning this species.

Shortfin mako

Isurus oxyrinchus

family

Lamnidae

taxonomy

Isurus oxyrinchus Rafinesque, 1810, Sicily, Mediterranean Sea.

other common names

French: Taupe bleu; Spanish: Marrajo dientuso.

physical characteristics

A slender shark, with long, slightly curved teeth devoid of lateral cusps, slightly elongated pectoral fin, very lunate caudal fin with well developed lower lobe, conical snout, eyes not very large, very small second dorsal, pelvic, and anal fins. Reaches close to 13.1 ft (4 m) in length. Bluish dorsally and laterally, and white ventrally as well as on caudal fin.

distribution

Worldwide in tropical to temperate waters.

habitat

An oceanic and littoral shark, found from the surface down to 1,640 ft (500 m).

behavior

The shortfin mako is probably the fastest and most agile of all sharks, jumping clear out of the water by several times its own length. Slightly endothermic, as its body musculature may reach up to 18° F (10° C) or more warmer than the temperature of the surrounding water. Highly migratory, capable of long-range migrations following warmer water masses.

feeding ecology and diet

Feeds mostly on fishes, both bony fishes as well as sharks and rays, squids, marine mammals, and turtles. Mako sharks are voracious feeders, consuming up to 3% of their body weight per day (compared to under 1% for many shark species), and digesting an average-sized meal in less than two days, whereas most sharks take some three to four days.

reproductive biology

Yolk-sac viviparous, with uterine cannibalism (oophagy), and litters ranging from four to as many as 30 young (usually between 10 and 18). Gestation period long (possibly from 15 to 18 months). Size at birth ranging from 23 to 27 in (60 to 70 cm). Age of maturity may be from seven to eight years old.

conservation status

Listed as Lower Risk/Near Threatened by the IUCN.

significance to humans

Shortfin makos are fished significantly in many areas worldwide, recreationally, artisanally, and industrially. Because of their highly active demeanor and size, shortfin makos may be dangerous, even though there are few incidents recorded, most of which are accidents while fishing and handling live individuals.

Porbeagle

Lamna nasus

family

Lamnidae

taxonomy

Squalus nasus Bonaterre, 1788, probably Cornwall, England.

other common names

French: Requin-taupe commun; Spanish: Marrajo sardinero.

physical characteristics

A somewhat stout shark, with a conical snout, large dark eyes, tips of pectoral fins slightly rounded, lunate caudal fin, teeth with small accessory cusps, bluish dorsal and lateral coloration (posterior tip of first dorsal white), and white ventrally. Reaches slightly over 9.8 ft (3 m) in length.

distribution

Occurs in warm, temperate, to cold waters in both the northern Atlantic, Mediterranean Sea, and in the Southern Hemisphere in the Atlantic and Indian Oceans, and off southern Australia.

habitat

An epipelagic, littoral, and oceanic shark, most abundant on offshore fishing banks, usually in colder waters. Occurs from 3 to 2,296 ft (1 to 700 m) in depth.

behavior

Porbeagles can be solitary or occur in schools. Usually migrates extensively at least in the northern Atlantic, and may aggregate by sex and size. An active, strong swimmer, capable of leaping out of water when captured.

feeding ecology and diet

Feeds mostly on fishes, both bony and cartilaginous, as well as on cephalopods. May be consumed by larger sharks.

reproductive biology

Yolk-sac viviparous, with uterine cannibalism confirmed (oophagy). Litters vary from one to five young (usually four), and gestation periods are estimated to last between eight and nine months. Young inside uterus may have fang-like teeth specialized for tearing egg cases to release eggs for consumption. The fang-like teeth are then shed in utero. Young are born 23.6–29.5 in (60–75 cm) in length.

conservation status

Listed as Lower Risk/Near Threatened by the IUCN.

significance to humans

Heavily fished for consumption, usually by longlining, but because of population declines, the porbeagle is now captured far less frequently. Overfishing is a concern especially in the North Atlantic, where the industry is regulated, but stocks may not be able to rebound. Recreationally fished as well, but individuals must be released upon capture. Not considered particularly dangerous to people.

Megamouth shark

Megachasma pelagios

family

Megachasmidae

taxonomy

Megachasma pelagios Taylor, Compagno, and Struhsaker, 1983, Hawaii.

other common names

French: Requin grand gueule; Spanish: Tiburón bocudo.

physical characteristics

A remarkable, very large shark, up to 18 ft (5.5 m) long, with a very wide mouth, extremely elongated jaws that reach to the tip of the snout (the lower jaw is slightly longer than the upper jaw), endowed with minute teeth, a large head region, relatively small eyes, dense, papillated gillrakers, very long pectoral fins, low dorsal fins, and a large caudal fin. Coloration grayish blue dorsally and whitish ventrally.

distribution

Known from some 17 specimens from Japan, the Philippines, western Australia, California, southeastern Brazil, Senegal, and South Africa. Probably circumglobal in warm temperate to tropical waters.

habitat

A coastal and oceanic inhabitant, found in shallow waters some 16 ft (5 m) deep as well as in deep waters offshore, down to 545 ft (166 m) in waters up to 15,092 ft (4,600 m) deep. One specimen was stranded on a beach after washing ashore.

behavior

A sluggish, solitary shark, capable of vertical migrations (perhaps following the movements of euphasiid shrimps). The megamouth shark is epipelagic but is capable of diving to great depths.

feeding ecology and diet

Feeds on zooplankton, especially euphasiid shrimp, copepods, and jellyfish, probably by taking in big gulps of water and retaining food on the very dense gillrakers. Luminous tissue lining the oral cavity may have a role in attracting prey items. Megamouths are the only known sharks with bite marks of the cookie-cutter shark (Isistius brasiliensis) and may be especially vulnerable because of their rather soft skin and slow-swimming behavior.

reproductive biology

Mostly unknown, but probably yolk-sac viviparous, as are other lamniforms. Pregnant females have not been captured. Small oocytes, 0.2–0.4 in (5–10 mm) in diameter, were present in the ovaries of an adult female. Bite marks matching the teeth of males also were present, and these have been interpreted as courtship scars.

conservation status

Listed as Data Deficient by the IUCN.

significance to humans

Caught occasionally as bycatch, but not consumed, though a Philippine specimen was apparently divided among fishermen. Of interest as a museum exhibit because of its extraordinary size and unusual features. The megamouth shark, only recently discovered, is one of the most spectacular ichthyological discoveries of the last 30 years and is the subject of a recent symposium volume, Biology of the Megamouth Shark, that provides much information on its anatomy and biology.

Goblin shark

Mitsukurina owstoni

family

Mitsukurinidae

taxonomy

Mitsukurina owstoni Jordan, 1898, Japan.

other common names

French: Requin lutin; Spanish: Tiburón duende.

physical characteristics

A very unique shark, with soft, flabby flesh, an extremely elongated, paddle-shaped snout endowed with numerous pores of the ampullary sensory system, jaws that protrude greatly, very long, slender, sharp teeth without lateral cusps, a large anal fin, small dorsal fins, and long and low caudal fin. Captured specimens are off-white to pinkish white all over. Reaches some 12.5 ft (3.8 m) in length.

distribution

Scattered distribution on the continental slope, but probably worldwide.

habitat

A deep water, oceanic (found on seamounts), and continental slope shark, reaching depths of at least 4,265 ft (1,300 m).

behavior

Mostly unknown, but a live specimen swam with its jaws tightly retracted, and not protruded as might have been expected.

feeding ecology and diet

Not well documented, but feeds on fishes and perhaps crustaceans.

reproductive biology

Unknown, as no pregnant females have ever been recorded, but presumed to be yolk-sac viviparous, as are other lamniforms.

conservation status

Not threatened.

significance to humans

Taken on longlines, mostly as bycatch, but not fished significantly. Not considered dangerous because of its deep-water habitat.

Sand tiger shark

Carcharias taurus

family

Odontaspididae

taxonomy

Carcharias taurus Rafinesque, 1810, Mediterranean Sea.

other common names

English: Gray nurse shark (Australia); French: Requin taureau; Spanish: Toro bacota.

physical characteristics

A relatively large shark, up to 9.8 ft (3 m) in length, with characteristic slender, sharp teeth (with lateral cusps), appearing to project outside of mouth (functional rows may point slightly forward), dorsal fins almost equal in size (first slightly larger), large anal fin, slightly rounded pectoral fin tips, conical snout, somewhat depressed head, clearly demarcated lateral line, and a light brown coloration, usually with slightly darker blotches scattered on body.

distribution

Distributed worldwide in tropical and warm temperate waters, but absent at least from the eastern Pacific, and probably also from the Caribbean and eastern North Atlantic (north of Africa).

habitat

Mostly an inshore species, found in shallow waters, but recorded to occur down to 627 ft (191 m), and may occur either close to the bottom, at the surface, or midwater.

behavior

Mostly nocturnal and solitary, but may form large schools, and capable of extensive migrations. Individuals aggregate for courtship, mating, feeding, and birth, and the sand tiger is capable of social interactions. Behavior in this species is known from aquarium observations, indicating that sand tiger sharks display specific patterns related to courtship and mating. These include specific movements of the claspers in males, submissive behavior by females, males poking the cloaca region of females with their snouts, and males biting females to establish dominance, among other behaviors. Sand tiger sharks will periodically gulp air into their stomachs from the surface, apparently as a buoyancy control.

feeding ecology and diet

Sand tiger sharks feed mostly on a wide range of fishes, including many families of pelagic and demersal bony fishes, as well as sharks and rays, cephalopods, crustaceans, and marine mammals.

reproductive biology

Yolk-sac viviparous, with embryos consuming other embryos (adelphophagy) and eggs in uteri. Gestation varies from 9 to twelve months. Two young are born in a litter, one per uterus, but a cluster of 16 to 23 eggs are grouped together in egg cases within each uterus after fertilization. From this group, only one embryo will be dominant, feeding on other embryos and eggs and even moving vigorously within the uterus. Young are born at about 3.3 ft (1 m) in length, but already have sharp teeth at 6.7 in (17 cm). Breeds every other year.

conservation status

Protected in Australian waters since 1984 because of steady declines in its populations as a result of overfishing, and listed as Vulnerable by the IUCN. Local protection measures are in place in many regions, including the eastern coast of the United States since 1997.

significance to humans

Commonly displayed in aquaria, where specimens can live for extended periods, surpassing 30 years. Not considered particularly dangerous, but because it appears ferocious, sand tigers have been implicated in attacks off Australia that are probably the result of other shark species. Observations conducted in the wild and in aquaria indicate that this species is harmless and presents no real danger to divers. Important to the ecotourism industry, as many trips feature observations of wild sand tiger sharks.

Crocodile shark

Pseudocarcharias kamoharai

family

Pseudocarchariidae

taxonomy

Carcharias kamoharai Matsubara, 1936, Japan.

other common names

French: Requin crocodile; Spanish: Tiburón crocodilo.

physical characteristics

A slender, relatively small shark up to 43 in (110 cm) in total length), with very large, blackish eyes, long, pointed teeth with minute lateral cusps only on lateral tooth rows (fewer than 30 total tooth rows in either jaw), pointed snout, low dorsal fins, and rounded pectoral fin tips.

distribution

Worldwide in tropical marine waters, but with a scattered distribution, needing confirmation from many areas.

habitat

Inhabits the tropical pelagic realm, but can occasionally be captured closer to shore. Reaches 984 ft (300 m) in depth.

behavior

Mostly unknown, but is believed to be a fast-swimming shark, probably capable of leaping out of the water. Its large eyes might indicate either nocturnal activity or feeding at great depths.

feeding ecology and diet

Feeds mainly on pelagic or mesopelagic fishes (e.g., bristle-mouths [Gonostomatidae], lanternfishes [Myctophidae]), and invertebrates such as squids.

reproductive biology

Yolk-sac viviparous, giving birth to four pups at a time (two per uterus). Uterine cannibalism has been recorded, with more developed fetuses eating remaining eggs, and, uniquely, two individuals surviving per uterus. Gestation periods mostly unknown.

conservation status

Considered at Lower Risk/Near Threatened by the IUCN.

significance to humans

Fished by longlines off Japan, but not significantly consumed. Because of its pelagic nature, there is little interaction with people, and hence the species is not considered dangerous.

Resources

Books

Applegate, S. P., and L. Espinosa-Arrubarrena. "The Fossil History of Carcharodon and Its Possible Ancestor, Cretolamna: A Study in Tooth Identification." In Great White Sharks: The Biology of Carcharodon carcharias, edited by A. P. Klimley and David G. Ainley, 19–36. San Diego, CA: Academic Press, 1996.

Bigelow, Henry B., and William C. Schroeder. "Sharks." In Fishes of the Western North Atlantic, Vol. 1, pt. 1 of Memoir of the Sears Foundation for Marine Research, 59–576. New Haven, CT: Yale University, 1948.

Branstetter, Steven, ed. Conservation Biology of Elasmobranchs. NOAA Technical Report, NMFS 115. Seattle, WA: U. S. Department of Commerce, 1993.

Burgess, G. H., and M. Callahan. "Worldwide Patterns of White Shark Attacks on Humans." In Great White Sharks: The Biology of Carcharodon carcharias, edited by A. Peter Klimley and David G. Ainley, 457–469. San Diego, CA: Academic Press, 1996.

Cappetta, Henri. Chondrichthyes II, Mesozoic and Cenozoic Elasmobranchii. Stuttgart, Germany: Gustav Fischer Verlag, 1987.

Carwardine, Mark, and Ken Watterson. The Shark Watcher's Handbook: A Guide to Sharks and Where to See Them. Princeton, NJ: Princeton University Press, 2002.

Compagno, Leonard J. V. "Relationships of the Megamouth Shark, Megachasma pelagios (Lamniformes: Megachasmidae), with Comments on Its Feeding Habits." In Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries, 357–379, edited by H. L. Pratt, Jr., S. H. Gruber, and T. Taniuchi. NOAA Technical Report, NMFS 90. Seattle, WA: U.S. Department of Commerce, 1990.

——. Bullhead, Mackerel and Carpet Sharks (Heterodontiformes, Lamniformes and Orectolobiformes), Vol. 2 of Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date. Rome, Italy: Food and Agriculture Organization of the United Nations, 2001.

Compagno, Leonard J. V., and V. H. Niem. "Families Odontaspididae, Pseudocarchariidae, Alopiidae, and Lamnidae." In Western Central Pacific Identification Sheets to Species, edited by Kent E. Carpenter and Volker H. Niem, 1264–1278. Rome, Italy: Food and Agriculture Organization of the United Nations, 1999.

Demski, Leo S., and John P. Wourms, eds. Reproduction and Development of Sharks, Skates, Rays and Ratfishes. Boston, MA: Kluwer Academic Publishers, 1993.

Ellis, Richard, and John E. McCosker. Great White Shark. New York: Harper Collins, 1991.

Francis, M. P. "Observations on a Pregnant White Shark with a Review of Reproductive Biology." In Great White Sharks:The Biology of Carcharodon carcharias, edited by A. Peter Klimley and David G. Ainley, 157–172. San Diego, CA: Academic Press, 1996.

Gottfried, M. D., Leonard J. V. Compagno, and S. C. Bowman. "Size and Skeletal Anatomy of the Giant 'Megatooth' Shark Carcharodon megalodon." In Great White Sharks: The Biology of Carcharodon carcharias, edited by A. Peter Klimley and David G. Ainley, 55–66. San Diego, CA: Academic Press, 1996.

Hamlett, William C., ed. Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. Baltimore, MD: Johns Hopkins University Press, 1999.

Hennemann, R. M. Sharks and Rays, Elasmobranch Guide of the World. Frankfurt, Germany: Ikan, 2001.

Klimley, A. Peter, and David G. Ainley, eds. Great White Sharks: The Biology of Carcharodon carcharias. San Diego, CA: Academic Press, 1996.

Last, P. R., and J. D. Stevens. Sharks and Rays of Australia. Melbourne, Australia: CSIRO Division of Fisheries, 1994.

Naylor, G. J. P., et al. "Interrelationships of Lamniform Sharks: Testing Phylogenetic Hypotheses with Sequence Data." In Molecular Systematics of Fishes, edited by Thomas D. Kocher and Carol A. Stepien, 199–218. San Diego, CA: Academic Press, 1997.

Nelson, J. Fishes of the World. 3rd ed. New York: John Wiley & Sons, 1994.

Perrine, Doug. Sharks & Rays of the World. Stillwater, MN: Voyageur Press, 1999.

Pratt, H. L. Jr., S. H. Gruber, and T. Taniuchi, eds. Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries. NOAA Technical Report, NMFS 90. Seattle: U. S. Department of Commerce, 1990.

Sibley, G., J. A. Seigel and C. C. Swift, eds. Biology of the White Shark, Vol. 9 of Memoirs of the Southern California Academy of Sciences. Los Angeles: 1985.

Springer, Victor G., and Joy P. Gold. Sharks in Question. The Smithsonian Answer Book. Washington, DC: Smithsonian Institution Press, 1989.

Stillwell, C. "The Ravenous Mako." In Discovering Sharks, edited by S. H. Gruber, 77–78. Highlands, NJ: American Littoral Society, 1990.

Whitley, G. P. The Sharks, Rays, Devil-fish, and Other Primitive Fishes of Australia and New Zealand. Pt. 1 of The Fishes of Australia. Sydney, Australia: Royal Zoological Society of New South Wales, 1940.

Yano, K., J. F. Morrissey, Y. Yabumoto, and K. Nakaya, eds. Biology of the Megamouth Shark. Tokyo, Japan: Tokai University Press, 1997.

Periodicals

Carey, F. G., et al. "Temperature, Heat Production, and Heat Exchange in Lamnid Sharks." Memoirs of the Southern California Academy of Sciences 9 (1985): 92–108.

Carey, F. G., et al. "The White Shark, Carcharodon carcharias, Is Warm-Bodied." Copeia 2 (1982): 254–260.

Eitner, B. J. "Systematics of the Genus Alopias (Lamniformes: Alopidae) with Evidence for the Existence of an Unrecognized Species." Copeia 3 (1995): 562–571.

Gilmore, R. G. "Reproductive Biology of Lamnoid Sharks." Environmental Biology of Fishes 38 (1993): 95–114.

Gilmore, R. G., J. W. Dodrill, and P. A. Linley. "Reproduction and Embryonic Development of the Sand Tiger Shark, Odontaspis taurus (Rafinesque)." Fishery Bulletin 81 (1983): 201–225.

Gruber, S. H., and Leonard J. V. Compagno. "Taxonomic Status and Biology of the Bigeye Thresher, Alopias superciliosus." Fishery Bulletin 79, no. 4 (1981): 617–640.

Hutchins, B. "Megamouth: Gentle Giant of the Deep." Australian Natural History 23, no. 12 (1992): 910–917.

Jordan, D. S. "A Classification of Fishes Including Families and Genera as far as Known." Stanford University Publications: Biological Sciences 3 (1923): 77–243.

Klimley, A. P. "The Areal Distribution and Autoecology of the White Shark, Carcharodon carcharias, off the West Coast of North America." Memoirs of the Southern California Academy of Sciences 9 (1985): 15–40.

——. "The Predatory Behavior of the White Shark." American Scientist 82, no. 2 (1994): 122–133.

Maisey, J. G. "Relationships of the Megamouth Shark, Megachasma." Copeia 1 (1985): 228–231.

Matthews, L. H. "Reproduction in the Basking Shark, Cetorhinus maximus." Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 234 (1950): 247–316.

McCosker, J. E. "White Shark Attack Behavior: Observations of and Speculations About Predator and Prey Strategies." Memoirs of the Southern California Academy of Sciences 9(1985): 123–135.

——. "The White Shark, Carcharodon carcharias, Has a Warm Stomach." Copeia 1 (1987): 195–197.

Taylor, L. R., Leonard J. V. Compagno, and P. J. Strusaker. "Megamouth—A New Species, Genus, and Family of Lamnoid Shark (Megachasma pelagios, Megachasmidae) from the Hawaiian Islands." Proceedings of the California Academy of Sciences 43 (1983): 87–110.

Tricas, T. C., and J. E. McCosker. "Predatory Behavior of the White Shark (Carcharodon carcharias), with Notes on Its Biology." Proceedings of the California Academy of Sciences 43(1984): 221–238.

Wourms, J. P. "Reproduction and Development in Chondrichthyan Fishes." American Zoologist 17 (1977): 379–410.

Organizations

American Elasmobranch Society, Florida Museum of Natural History. Gainesville, FL 32611 USA. Web site: <http://www.flmnh.ufl.edu/fish/Organizations/aes/aes.htm>

Marcelo Carvalho, PhD