A sawshark or saw shark is a member of a shark order (Pristiophoriformes) bearing a unique long, saw-like rostrum (snout or bill) edged with sharp teeth, which they use to slash and disable their prey.

Sawsharks are found in many areas around the world, most commonly in waters from the Indian Ocean to the southern Pacific Ocean. They are normally found at depths around 40–100 m, but can be found much lower in tropical regions. The Bahamas sawshark was discovered in deeper waters (640 m to 915 m) of the north-western Caribbean.

Sawsharks have a pair of long barbels about halfway along the snout. They have two dorsal fins, but lack anal fins. Genus Pliotrema has six gill slits, and Pristiophorus the more usual five. The teeth of the saw typically alternate between large and small. Saw sharks reach a length of up to 5 feet and a weight of 18.7 pounds, with females tending to be slightly larger than males.

The body of a longnose saw shark is covered in tiny placoid scales: modified teeth covered in hard enamel. The body is a yellow-brown color which is sometimes covered in dark spots or blotches. This coloration allows the saw shark to easily blend with the sandy ocean floor.

These sharks typically feed on small fish, squid, and crustaceans, depending on species. The function of the sawshark barbels are not well understood, and neither is how they use their rostrum. It is possible they use it in a similar fashion as sawfishes, and hit prey with side-to-side swipes of the saw, crippling them. The saw could also be utilized against other predators in defense. The saw is covered with specialized sensory organs (ampullae of Lorenzini) which detect an electric field which is given off by buried prey.

Saw sharks life history is still poorly understood. Mating season occurs seasonally in coastal areas. Saw sharks are ovoviviparous meaning eggs hatch inside the mother. They have litters of 3–22 pups every 2 years. After 12 months of pregnancy, the pups are born at 30 cm long. While in the mother, pups’ rostral teeth are angled backwards to avoid harming the mother. The life expectancy of sawsharks is still poorly understood, but they are thought to live to 10 years or more.

Chlamydoselachidae is a family of primitive deep-sea sharks in the order Hexanchiformes. They are one of only two extant families in the order alongside the cow sharks in the family Hexanchidae, and the only members of the suborder Chlamydoselachoidei.

Frilled shark

The habitats of the frilled shark include the waters of the outer continental shelf and the upper-to-middle continental slope, favoring upwellings and other biologically productive areas. Usually, the shiver lives close to the ocean floor, yet its diet of cephalopods, smaller sharks, and bony fish, indicates that the frilled shark practices diel vertical migration, and swims up to feed at night at the surface of the ocean. In their Atlantic- and Pacific-ocean habitats, frilled sharks practice spatial segregation determined by the individual size, the sex, and the reproductive condition of each shark in the shiver. In Suruga Bay, on the Pacific coast of Honshu, Japan, the frilled shark is most common at the depth of 50–200 m, except in the August-to-November period, when the temperature at the 100 m water-layer exceeds 15 °C, and then the sharks swim into deeper, cooler water.

In the eastern Atlantic Ocean, the frilled shark occurs off northern Norway, northern Scotland, and western Ireland, ranging from France to Morocco, the archipelago of Madeira, and the coast of Mauritania, in northwest Africa. In the central Atlantic Ocean, the frilled shark has been caught along the region of the Mid-Atlantic Ridge, ranging from north of the Azores islands to the Rio Grande Rise, off southern Brazil, and the Vavilov Ridge, off West Africa. Frilled sharks tend to be very solitary organisms; interacting with multiple individuals of their kind is rare. However, in the late 2000s a large capture was made over an underwater seamount of the Mid-Atlantic Ridge, hauling in over 30 frilled sharks. The mass capture of a wide variety of male and female specimens emphasized these seamounts as a location for the mating of the species. In the western Atlantic, the frilled shark occurs in the waters of New England and Georgia, in the US, and in the waters of Suriname, in the northeastern coast of South America.

In the western Pacific Ocean, the frilled shark ranges from southeastern Honshu, Japan, north to Taiwan, off the coast of China, to the coast of New South Wales, Australia, and the islands of Tasmania and New Zealand. In the central and eastern Pacific Ocean, the frilled shark occurs in the regional waters of Hawaii and the coast of California, in the US, and the northern coast of Chile, in western South America. Although it has been caught at the depth of 1,570 m, the frilled shark usually does not occur deeper than 1,000 m.

The head of the frilled shark is broad and flat, with a short, rounded snout. The nostrils are vertical slits, separated by a flap of skin that forms the incurrent opening and the excurrent opening. The moderately large eyes are horizontal ellipsoids, which have no nictitating membrane, which is a protective, third eyelid. Ligaments articulate the long jaws to the cranium, and the corners of the mouth have neither furrows nor folds. The jaws contain 300 trident-shaped teeth, each needle-tooth has a cusp and two cusplets; the rows of teeth are widely spaced, with 19–28 tooth rows in the upper jaw, and 21–29 tooth rows in the lower jaw. Frilled sharks are able to open their jaws and devour food sources that are considerably larger than their own body size, a physical trait that is also present in gulper eels and viperfish. At the throat, there are six pairs of long gill slits; the first pair of gill slits form a collar, while the extended tips of the gill filaments create a fleshy frill, hence, the frilled shark name of this fish.

The pectoral fins are short and rounded; the single, small dorsal fin has a rounded margin, and is positioned at the far end of the body, approximately opposite the anal fin. The pelvic and the anal fins are large, broad and rounded, and are positioned to the tail-end of the frilled shark’s body. The very long caudal fin is a triangular tail that has neither a lower lobe nor a ventral notch in the upper lobe, and has a margin equipped with sharp, chisel-shaped dermal denticles, which the shark can enlarge. The underside of the shark’s eel-like body features a pair of long, thick folds of skin, separated by a groove, which run the length of the belly; the function of the ventral skin-folds is unknown. In the female frilled shark, the mid-section of the body is longer, with the pelvic fins located closer to the anal fin.

A cartilaginous skeleton and a large liver (filled with low-density lipids) are the mechanical means with which the frilled shark controls and maintains its buoyancy in the deep waters of the ocean. The shark has an open, lateral-line organ system featuring mechanoreceptor hair cells in grooves exposed to the ocean environment; such a basal clade configuration enhances the frilled shark’s perception and detection of changes in the movement, the vibration, and the pressure of the surrounding water. Like all animals, the frilled shark is afflicted by parasites, such as the Monorygma tapeworm, the trematoda flatworm, the Otodistomum veliporum, and the Mooleptus rabuka nematode; and by predators, such as other sharks, as indicated by missing tail-tips lost to a hungry attacker.

The frilled shark eats a diet of cephalopods, Nudibranchs, smaller sharks, and bony fish; 60 percent of the diet is composed of squid varieties, such as the Chiroteuthis, the Histioteuthis, and the Onychoteuthis, the Sthenoteuthis and the Todarodes; and other sharks, as indicated by the stomach contents of a 1.6 m–long frilled shark which had swallowed a 590 g Japanese catshark (Apristurus japonicus). The high tendency to primarily consume the squids in their habitat can be supported by the frequent observation of beak remnants left behind during digestive processes. Because frilled sharks live on the ocean floor, they may also feed on carrion floating down from the surface.

In hunting and eating prey that are tired or exhausted or dying (after spawn), the frilled shark’s physiology suggests that it may curve its anguilline body, and brace its rear fins against the water, for leverage to effect a rapid-strike bite that captures the prey. The wide gape of the distended, long jaws allows devouring whole prey that are more than half the size of the frilled shark, itself. The jaws’ 300 recurved teeth (19–28 upper rows and 21–29 lower rows) readily snag and capture the soft body and tentacles of a cephalopod, especially with the rows of trident-shaped teeth are rotated outwards, when the jaws are open and protruded. Moreover, unlike the strong bite of sharks with an underslung jaw attached below the cranium, the frilled shark has a relatively weak bite, because of the limited leverage and force possible with long jaws that are directly articulated to the cranium, at a point behind the eyes.

The extant species of frilled shark, C. anguineus and C. africana, do not have a defined breeding season, because their oceanic habitats register no seasonal influence from the ocean’s surface; the male shark reaches sexual maturity when he is 1.0–1.2 m long, and the female shark reaches sexual maturity when she is 1.3–1.5 m long. The mature female shark has two ovaries and a uterus, which is in the right side of her body; ovulation occurs fortnightly; and pregnancy ceases vitellogenesis (yolk formation) and the production of new ova. Both ovulated eggs and early-stage shark embryos are enclosed in chondrichthyes, ellipsoid egg-cases made of a thin, golden-brown membrane.

Reproductively, the frilled shark is an ovoviviparous animal born from an encapsulated egg retained within the mother shark’s uterus. During gestation, the shark embryos develop in membranous egg-cases contained within the body of the mother shark, when the infant sharks emerge from their egg capsules in the uterus they feed on yolk until birth. The frilled-shark embryo is 3.0 cm long, has a pointed head, slightly developed jaws, nascent external gills, and possesses all fins. The growth of the jaw for elasmobranchs seem to begin early in the embryonic stage, however, it has been observed not to be the case for frilled sharks. The elongation of the jaws seemed to begin later in embryonic development. This leads to some studies suggesting that the terminal position of their mouth, due to anterior elongation of the jaw, is a derived trait instead of ancestral. When the embryo is 6–8 cm long, the mother shark expels the egg capsule, at which developmental stage the frilled shark’s external gills are developed. Throughout embryonic development, the size of the yolk sac remains constant, until the shark embryo is 40 cm long, whereupon the sac shrinks until disappearing when the embryo has grown to 50 cm in length. In the course of pregnancy, the embryo’s average rate-of-growth is 1.40 cm per month until birth, when the shark pups are 40–60 cm long, therefore, the frilled shark’s gestation period can be as long as 3.5 years; at birth, a frilled shark’s litter comprises 2–15 pups, with an average litter comprises 6.0 pups.

Southern African Frilled Shark

The southern African frilled shark is found from off the coast of southern Angola to Namibia and South Africa. Frilled sharks have also been captured off South Africa, at 1,230–1,400 m deep off Eastern Cape Province, and at 300 m deep off KwaZulu-Natal Province; it is uncertain whether these specimens are C. africana. Little is known of its habitat preferences; one known specimen was caught 425 m down in a zone of low dissolved oxygen and high nutrients, over a soft substrate.

The southern African frilled shark looks very similar to the frilled shark, with a long snake-like body and a broad, flattened head. The eyes are large and rounded. The sizable mouth is placed terminally on the blunt snout, containing around 30 tooth rows in the upper jaw and 27 tooth rows in the lower jaw. Each tooth has three slender, smooth, recurved cusps, with tiny cusplets between them, and a base that interlocks with the tooth behind it. There are six pairs of long gill slits, with the first pair meeting over the throat. The pectoral fins are broad and rounded, originating just behind the sixth gill slit. The pelvic and anal fins are large with long bases and curved margins. The single dorsal fin is set far back on the body over the anal fin, and has a short base. The caudal fin is low and somewhat triangular, without a lower lobe.

The southern African frilled shark looks very similar to the frilled shark, with a long snake-like body and a broad, flattened head. The eyes are large and rounded. The sizable mouth is placed terminally on the blunt snout, containing around 30 tooth rows in the upper jaw and 27 tooth rows in the lower jaw. Each tooth has three slender, smooth, recurved cusps, with tiny cusplets between them, and a base that interlocks with the tooth behind it. There are six pairs of long gill slits, with the first pair meeting over the throat. The pectoral fins are broad and rounded, originating just behind the sixth gill slit. The pelvic and anal fins are large with long bases and curved margins. The single dorsal fin is set far back on the body over the anal fin, and has a short base. The caudal fin is low and somewhat triangular, without a lower lobe.

Compared to the frilled shark, the southern African frilled shark has several proportional differences, including a longer head and gill slits, more widely spaced eyes and nares, broader mouth, and a greater distance between the head and the pectoral fins. The largest known female is the immature 117 cm long holotype, and the largest known males measure 99 cm long. In life the shark is dark gray, but covered with a thin membrane that gives it a uniform dark brown color.

From stomach contents, the southern African frilled shark seems to feed mainly on smaller sharks such as the African sawtail catshark (Galeus polli). Its jaws, buccal cavity, and abdomen are all highly distensible, suggesting that this shark is specialized for capturing and swallowing whole large prey, with its rows of needle-like, recurved teeth preventing escape. One 92 cm long specimen was found to have swallowed a ghost catshark (Apristurus sp.) that measured 40% of its body length.

Although adult females are unknown, the southern African frilled shark is presumed to be aplacental viviparous like the frilled shark. Males mature sexually at a length of 91.5 cm.

Echinorhinus is the only extant genus in the family Echinorhinidae, either a family within the large order Squaliformes or their own monotypic order Echinorhiniformes. The two extant species possess enlarged denticles forming prominent spines or thorns on their skin.

Bramble shark

The bramble shark (Echinorhinus brucus) is one of the two species of sharks in the family Echinorhinidae. Aside from the eastern Pacific Ocean, it is found in tropical and temperate waters worldwide. This rarely encountered shark swims close to the bottom of the seafloor, typically at depths of 400–900 m, though it may enter much shallower water. The bramble shark has a stout body with two small dorsal fins positioned far back and no anal fin. It can be readily identified by the large, thornlike dermal denticles scattered over its body, some of which may be fused together. It is purplish brown or black in color and grows up to 3.1 m long.

Sluggish in nature, the bramble shark feeds on smaller sharks (including the spiny dogfish, Squalus acanthias), bony fishes (including ling, catfishes, and lizardfishes), and crabs. The large size of its pharynx, relative to its mouth, suggests that it may capture prey by suction. This species is aplacental viviparous; females have two functional ovaries and two uteruses. Recorded litter sizes have ranged from 15 to 52, and newly born pups have been estimated to measure 40–50 cm long. The size of litters has been observed to vary by region. The dermal denticles in near-term embryos are underdeveloped, appearing as minute spines located within open pits in the skin.

Prickly shark

The prickly shark has a flabby and cylindrical body, with the adults markedly bulkier than juveniles, and a short, moderately flattened head. The nostrils are placed far apart and preceded by small flaps of skin. The spiracles are tiny and positioned well behind the eyes, which lack nictitating membranes. The mouth forms a broad arch, with very short furrows at the corners. There are 21–25 and 20–27 tooth rows in the upper and lower jaws respectively. The knife-like teeth each have a strongly angled main cusp flanked by up to three smaller cusplets on either side; the lateral cusplets are absent in young sharks. There are five pairs of gill slits, with the fifth pair the longest.

The lateral line runs along each side of body in a conspicuous furrow. The pectoral fins are short, while the pelvic fins are relatively large with long bases. The first dorsal fin is small and originates at or behind the level of the pelvic fin origins; the second dorsal fin is similar to the first and positioned close behind. The anal fin is absent, and the stout caudal peduncle lacks depressions at the caudal fin origins. The caudal fin has a longer upper lobe without a notch in the trailing margin, and an indistinct lower lobe. The skin has a dense, uniform covering of non-overlapping dermal denticles measuring up to 0.4 cm across, which are never fused together as in the bramble shark. Each denticle is thornlike, with strong ridges running down the central spine and radiating out over the star-shaped base. The denticles beneath the snout are very fine in adults. The prickly shark is plain brown or gray, often with a purplish tint, and has black trailing margins on the fins. The underside is paler, most obviously on the snout and around the mouth.

The prickly shark is widely distributed around the Pacific Ocean. In the western and central Pacific, it has been reported off Japan, Taiwan, Victoria and Queensland in Australia, and New Zealand, as well as around the islands of Palau, New Caledonia, Tonga, Hawaii, and possibly the Gilberts. In the eastern Pacific, it is known to occur from Oregon to El Salvador (including the Gulf of California), around the Cocos and Galapagos Islands, and off Peru and Chile. This species generally seems to be uncommon; an exception is in Monterey Canyon off California, where sharks of both sexes are abundant throughout the year.

Favoring cooler temperatures of 5.5–11 °C, the prickly shark is mostly found below depths of 100–200 m, particularly in the tropics. It has been recorded from at least 650 m down and may occur much deeper, possibly to 1,500 m. On the other hand, at higher latitudes it frequently enters shallow inshore waters; for example, in Monterey Canyon it can be consistently found at depths of 15–35 m, and off Moss Landing one individual was captured in water only 4 m deep. This shark inhabits continental and insular shelves and slopes, where it swims close to the bottom. It can also be found inside submarine canyons, close to the walls. It prefers areas with a muddy or sandy substrate. It is tolerant of low dissolved oxygen levels, allowing it to inhabit oceanic basins inaccessible to other sharks.

The prickly shark is a slow swimmer and has been observed hovering just above the sea floor. A tracking study in Monterey Canyon found that this species exhibits strong diel migration patterns. The sharks were inactive during the day, resting in discrete refuge areas located near the sea floor in deep, offshore waters. They became active at dusk, swimming towards the coast to the head of the canyon and rising into the water column; this upward movement is likely related to feeding on schooling fishes. Individual sharks seldom strayed from the local area and had very small home ranges, no more than 2.2 km² . The prickly sharks in Monterey Canyon regularly form aggregations that may number over thirty.

The size and structure of the prickly shark’s mouth and pharynx suggests that it uses suction to capture prey. This species feeds on a variety of benthic and pelagic bony fishes, including hake, flounders, rockfishes, lingcod, topsmelt, mackerel, and herring, and on cartilaginous fishes, including elephantfishes (Callorhinchus), spiny dogfish (Squalus acanthias), young bluntnose sixgill sharks (Hexanchus griseus), and ghost catshark (Apristurus) egg cases. Octopuses and squid, including the Humboldt squid (Dosidicus gigas) are also consumed. Young prickly sharks may themselves fall prey to the bluntnose sixgill shark, while adults likely face few threats. Reproduction in this species is aplacental viviparous, with the unborn young sustained by yolk. There is only one known record of a pregnant female, which was gestating 114 embryos; this ranks among the largest known litters from any shark. The young are probably under 40 cm long at birth. The length at sexual maturity has not been precisely determined but is thought to be around 2.0 m for males and 2.5–3.0 m for females.

Wobbegong is the common name given to the 12 species of carpet shark in the family Orectolobidae. They are found in shallow temperate and tropical waters of the western Pacific Ocean and eastern Indian Ocean, chiefly around Australia and Indonesia, although one species (the Japanese wobbegong, Orectolobus japonicus) occurs as far north as Japan.

The word wobbegong is thought to come from an Australian Aboriginal language and means shaggy beard, referring to the growths around the mouth of the shark.

Wobbegongs are bottom-dwelling sharks, spending much of their time resting on the sea floor. Most species have a maximum length of 1.25 m, but the largest, the spotted wobbegong, Orectolobus maculatus, and banded wobbegong, Orectolobus halei, reach about 3 m in length.

Wobbegongs are well camouflaged by a symmetrical pattern of bold markings resembling a carpet. Because of this striking pattern, wobbegongs and their close relatives are often referred to as carpet sharks.

The camouflage is improved by the presence of small, weed-like whisker lobes surrounding the wobbegong’s jaw, which help to camouflage it and act as sensory barbs. Wobbegongs make use of their camouflage to hide among rocks and catch smaller fish that swim too close, typical of ambush predators. Wobbegongs also have powerful jaws with needle-like teeth to assist in catching reef fish and other sharks for food. The blood cells of several species of wobbegongs have been described.

Wobbegongs are generally not considered dangerous to humans but have attacked swimmers, snorkelers, and scuba-divers, who inadvertently come close to them. The Australian Shark Attack File contains more than 50 records of unprovoked attacks by wobbegongs and the International Shark Attack File has 31 records, none of them fatal. Wobbegongs have also bitten surfers. Wobbegongs are very flexible and can easily bite a hand holding their tail. They have many small but sharp teeth and their bite can be severe, even through a wetsuit; having bitten, they have been known to hang on and can be very difficult to remove.

The Hemiscylliidae are a family of sharks in the order Orectolobiformes, commonly known as longtail carpet sharks and sometimes bamboo sharks. They are found in shallow waters of the tropical Indo-Pacific.

They are relatively small sharks, with the largest species reaching no more than 121 cm in adult body length. They have elongated, cylindrical bodies, with short barbels and large spiracles. As their common name suggests, they have unusually long tails, which exceed the length of the rest of their bodies. They are sluggish fish, feeding on bottom-dwelling invertebrates and smaller fish. Bamboo sharks make noises such as popping and sucking when feeding, clicking jaws when handled as a stress signal and hissing by expelling water from their gills.

Chiloscyllium

This genus is distinguished by a relatively long snout with subterminal nostrils. The eyes and supraorbital ridges are hardly elevated. The mouth is closer to the eyes than to the tip of the snout, with lower labial folds usually connected across the chin by a flap of skin. The pectoral and pelvic fins are thin and not very muscular. No black hood on the head or large black spot on the side is present (though juveniles often are strongly marked with dark spots/bars).

Hemiscyllium

This genus is confined to tropical waters of Australia, Papua New Guinea, and Indonesia, but an individual from this genus, possibly representing an undescribed species, has been photographed at the Seychelles. They have short snouts with the nostrils placed almost at the tip, and well-elevated eyes and supraorbital ridges. The mouth is closer to the tip of the snout than the eyes, and lacks the connecting dermal fold across the chin. The pectoral and pelvic fins are thick and heavily muscular. Either a black hood on the head or a large black spot on the sides of the body is present.

The Ginglymostomatidae are a cosmopolitan family of carpet sharks known as nurse sharks, containing four species in three genera. Common in shallow, tropical, and subtropical waters, these sharks are sluggish and docile bottom dwellers. They are the most abundant species of shark found in shallow coastal waters. Nurse sharks typically attack humans only if directly threatened.

Description

The largest species, called simply the nurse shark Ginglymostoma cirratum, may reach a length of 4.3 m; the tawny nurse shark Nebrius ferrugineus is somewhat smaller at 3.2 m, and the short-tail nurse shark Pseudoginglymostoma brevicaudatum is by far the smallest at just 75 cm in length. The first of the three species may reach a weight of 110 kg. Yellowish to dark brown in colour, nurse sharks have muscular pectoral fins, two spineless dorsal fins (the second of which is smaller) in line with the pelvic and anal fins, and a tail exceeding one quarter the shark’s body length.

The mouth of nurse sharks is most distinctive; it is far ahead of the eyes and before the snout (subterminal), an indication of the bottom-dwelling (benthic) nature of these sharks. Also present on the lower jaw are two fleshy barbels, chemosensory organs that help the nurse sharks find prey hidden in the sediments. Behind each eye is a very small, circular opening called a spiracle, part of the shark’s respiratory system. The serrated teeth are fan-shaped and independent; like other sharks, the teeth are continually replaced throughout the animal’s life.

Habits

Nurse sharks are nocturnal animals, spending the day in large inactive groups of up to 40 individuals. Hidden under submerged ledges or in crevices within the reef, the nurse sharks seem to prefer specific haunts and return to them every day. By night, the sharks are largely solitary; they spend most of their time searching through the bottom sediments in search of food. Their diet consists primarily of crustaceans, molluscs, tunicates, and other fish, particularly stingrays.

Nurse sharks are thought to take advantage of dormant fish, which would otherwise be too fast for the sharks to catch; although their small mouths limit the size of prey items, the sharks’ large throat cavities are used as a sort of bellows valve. In this way, nurse sharks are able to suck in their prey. Nurse sharks are also known to graze algae and coral.

Reproduction

The mating season runs from late June to the end of July. All nurse sharks are aplacental viviparous, meaning the eggs develop and hatch within the body of the female, where the hatchlings develop further until live birth occurs. The gestation period is six months, with a typical litter of 30–40 pups. The mating cycle is biennial, as 18 months are needed for the female’s ovaries to produce another batch of eggs. The young nurse sharks are born fully developed at about 30 cm long in Ginglymostoma cirratum. They possess a spotted coloration that fades with age.

Sand sharks are mackerel sharks of the family Odontaspididae. They are found worldwide in temperate and tropical waters. The family contains two species in a single extant genus (Odontaspis), as well as several extinct genera. The genus Carcharias was formerly included in the family.

The body tends to be brown with dark markings in the upper half. These markings disappear as they mature. Their needle-like teeth are highly adapted for impaling fish, their main prey. Their teeth are long, narrow, and very sharp with smooth edges, with one and on occasion two smaller cusplets on either side. Sand sharks have a large second dorsal fin.

Location and origins

The name sand shark comes from their tendency to migrate toward shoreline habitats, and they are often seen swimming around the ocean floor in the surf zone; at times, they come very close to shore. They are often found in warm or temperate waters throughout the world’s oceans, except the eastern Pacific. They also frequent the Mediterranean and Adriatic Seas at depths from 20 to 200 m and sometimes more.

Behavior

The sand shark has a unique hunting strategy. It is able to gulp air from above the surface and collect the air in its stomach. This enables it to become buoyant and approach its prey virtually motionless. During the day, the sand shark stays mostly inactive, but at night, it becomes active and resumes hunting activities. Its staple is small fish, but it eats crustaceans and squid, as well. It occasionally hunts in shivers (groups), and has even been known to attack full fishing nets.

Reproduction

Sand sharks only develop two embryos, one in each uterus. The largest and strongest embryos consume their siblings in the womb (intrauterine cannibalism) before each surviving pup is born. It has one of the lowest reproduction rates of all sharks and is susceptible to even minimal population pressure, so it is listed as vulnerable and is protected in much of its range.

Attacks on people

Sand sharks are not known to attack humans. If a person were to provoke a sand shark, it may retaliate defensively. Sand sharks are generally not aggressive, but harass divers who are spearfishing. In North America, wreck divers regularly visit the World War II shipwrecks to dive with the sharks that make the wrecks their home.

The Lamnidae are the family of mackerel sharks known as white sharks. They are large, fast-swimming predatory fish found in oceans worldwide, though they prefer environments with colder water. The name of the family is formed from the Greek word lamna, which means “fish of prey”, and was derived from the Greek legendary creature, the Lamia.

These sharks have pointed snouts, spindle-shaped bodies, and large gill openings. The first dorsal fin is large, high, stiff and angular or somewhat rounded. The second dorsal and anal fins are minute. The caudal peduncle has a couple of less distinct keels. The teeth are gigantic. The fifth gill opening is in front of the pectoral fin and spiracles are sometimes absent. They are powerful, heavily built sharks, sometimes weighing nearly twice as much as other sharks of comparable length from other families. Many sharks in the family are among the fastest-swimming fish, although the massive great white shark is slower due to its large size.

Carcharodon

The great white shark (Carcharodon carcharias), also known as the white shark, white pointer, or great white, is a large shark. It is closely related to the mako sharks, the porbeagle, and the salmon shark. It is a robustly built species with a grayish upperside and a white underside. The white shark is one of the largest living shark and fish species, though it is still smaller than the whale shark and basking shark. It has about 300 triangular, serrated teeth that are continuously replaced. Its massive, fatty liver can reach over a quarter of its body weight, providing buoyancy and storing energy. The species is partially warm-blooded, an adaptation that allows it to remain active in colder waters.

White sharks inhabit tropical and temperate ocean waters around the world and can be found both near coasts and in the open ocean. Populations are most concentrated at the Pacific and Atlantic sides of North America and in the waters of southern Africa and Oceania. They are a highly migratory species, traveling between the coast and the open ocean and even between continents. The white shark preys on marine mammals such as seals and dolphins, as well as squid and fish, including other sharks. It also scavenges whale carcasses. Though normally an apex predator, the species is sometimes preyed on by orcas. White sharks are generally solitary, but may gather in aggregations, particularly at feeding sites. They may communicate and establish dominance hierarchies with body language. The species reproduces with pups hatching from eggs inside the female before being born live. Juvenile white sharks typically inhabit shallower water and are limited to feeding on smaller prey.

The white shark has a fearsome reputation among the public. In reality, white sharks normally do not prey on humans, and the majority of bites are due to curiosity or possibly mistaken identity. Many attempts have been made to keep the species in captivity, but specimens either ended up dying or being released. White shark aggregations have attracted tourists who may view them from boats or from inside shark cages.

Isurus

Mako sharks are predatory mackerel sharks of the genus Isurus (meaning “equal tail”). They are largely pelagic, and are fast, predatory fish capable of swimming at speeds of up to 50 km/h. They occur at depths of 50–250 m. When hunting, they are capable of powerful leaps above the water surface. They feed primarily on bony fishes, sea turtles, other marine animals, and cephalopods. Both mako sharks are sexually dimorphic, with females being larger than males, and are large sharks. Both species of mako shark are classified as “Endangered” by the IUCN.

Reproduction is viviparous, with females producing litters of up to 18 pups measuring 70–120 cm at birth.

Lamna

Lamna is a genus of mackerel sharks in the family Lamnidae, containing two extant species: the porbeagle (Lamna nasus) of the North Atlantic and Southern Hemisphere, and the salmon shark (Lamna ditropis) of the North Pacific.

The total length of representatives of this genus ranges from 2 to 3.5 m, with a body mass of 25–31 kg. Males are somewhat smaller than females. The head is conical, and the mouth is large, with 25–31 rows of teeth. The eyes are large and positioned on the upper part of the head. There are five gill slits. The body is robust. One anal fin is present, along with one or two dorsal fins. The pectoral fins are broad. Coloration is bluish or brown on the back and sides, with a lighter underside marked by numerous dark spots.

Mackerel sharks inhabit generally shallow waters, down to a maximum depth of about 650 m, and may form small groups. They are capable of tolerating low temperatures, down to −15 to −18 °C. Their diet consists mainly of small to medium-sized bony fishes.

Sexual maturity in males occurs between 2 and 12 years of age, while females typically mature earlier. These sharks are ovoviviparous, with females giving birth to litters of 2–5 pups measuring 40–75 cm in length. Life expectancy is up to about 65 years.