how are some sharks warm blooded

The Salmon Shark is one of the warmest of the warm-bodied sharks. Measurements of its epaxial (upper back) muscles indicate that this species is able to maintain a body temperature 14 to 20 degrees Fahrenheit (8 to 11 degrees Celsius) above the ambient water temperature.

Biology of the Salmon Shark

"Biology of the Salmon Shark ( Lamna ditropis)Field Marks Body stocky, spindle-shaped; snout conical and short (distance from tip of snout to eye is about 40% distance from eye to first gill slit); teeth moderately large, blade smooth-edged with basal cusplets; gill slits long, extending partially onto top of head; first dorsal fin originating over axil ('armpit') of pectoral fins and with dark free rear tip; second dorsal and anal fins minute, with pivoting bases; strong keels on caudal peduncle (tail stalk), with a short secondary keel on each side of the caudal fin base; caudal fin lunate, with lower lobe almost as long as the upper.

Color: dark bluish grey to bluish black above, underside of snout, lower jaw, and belly whitish with dark greyish blotches in individuals longer than about 5 ft (1.5 m). Size Pups are born at a length of about 31.5-34.3 in (80-87 cm); most individuals caught or encountered are 6-7.5 ft (1.8-2.3 m) in length; maximum recorded length for males is 6.2 ft (1.9 m) and for females is 7.0 ft (2.14 m), although the species reported to reach a length of up to 12.1 ft (3.7 m) and a weight of up to 1 000 lbs (454 kg).

Range Widely distributed in the North Pacific north of 35°, though apparently not found in the East China Sea and Yellow Sea (as indicated by Compagno 1984).

Habitat Common in coastal-littoral and epipelagic zones of boreal to cool temperate waters; found from the surface to a depth of at least 500 ft (152 m), with most catches at a depth of about 130 ft (40 m) in the Gulf of Alaska and 100-350 ft (92-107 m) elsewhere; while common offshore, this species sometimes comes close inshore, just off the breakers, and occasionally strands; partially endothermic, able to maintain its body temperature 14.5-20°F (8-11°C) above ambient; known water temperature range 38.3-72.5°F (3.5-22.5°C), with most catches recorded at about 57°F (14°C); known salinity range 31.5-34.25‰ (ppt).

Catch data provide evidence of segregation by size and sex in the western North Pacific; usually solitary, but may aggregate at night and when feeding, sometimes forming schools of 30-40 individuals; adults highly migratory in some parts of the species' range, but juveniles do not appear to migrate.

Feeding Primarily piscivorous, but also known to take squids, shrimps and benthic crabs; notorious as a predator on Pacific salmon ( Oncorhynchus spp), although researchers differ on how significant these sharks are as a source of natural mortality; known non-salmonid fish prey in subarctic waters include daggereeth, lancetfish, Atka mackerel, and lumpsuckers in northern waters, and pollock, sauries, Spiny Dogfish ( Squalus acanthias ), lanternfishes, pomfret, and chub mackerel in southern.

Non-fish prey includes oceanic squids as well as benthic crustaceans such as shrimps, and tanner crabs ( Chionoecetes sp.).

In summer and fall, large individuals migrate to the northern Sea of Japan to feed on pilchards; in Sea of Okhotsk and Bering Sea, feed on pollock during fall.

Reproduction Ovoviviparous, featuring oophagy at late stage of development; litter size typically 4-5; in western Pacific, pups are born during spring (March-May) in offshore waters, northeast of Honshu and south of the Kuril Islands; juveniles 27-43 in (70-110 cm) long abundant north of the subarctic boundary, which may serve as a nursery area; mating apparently takes place during autumn (September-November); in eastern Pacific (off Alaska), pups are born in May after a gestation period of about 1 yr. Age & Growth Pups grow to a length of 47-55 in (120-140 cm) by the end of their first year, an increase of up to 75%; subsequent annual growth is 4-6 in (10-15 cm) per year up to age 4; for age 5 and older, females grow faster than males, attaining a length of 7.2 ft (2.2 m) at age 10, compared with 6.9 ft (2.1 m) for males of the same age; males mature at a length of about 6 ft (1.8 m) and an age of about 9-10 yrs, females at a length of about 7.2-7.5 ft (2.3-2.3 m) and an age of about 10-11 yrs; longevity for males is estimated to be 25 yrs, and for females 17 yrs.

Danger to Humans Regarded as potentially dangerous due to its large size and relationship to species known to be dangerous; seldom implicated in attacks on humans - the SAF currently lists no attacks definitely attributable to this species (a few unsubstantiated attacks attributed to it, but these may be due to confusion with the White Shark [ Carcharodon carcharias ]). Recently, divers have encountered and photographed schools of this species underwater, with no aggressive or threatening behavior exhibited by the sharks. Utilization Fished in the North Pacific by Japanese coastal longliners and by sports anglers in Alaska and British Columbia, Canada, using rod and reel; commonly caught by Japanese, US, and Canadian offshore salmon gillnetters, but are usually discarded; occasionally trammel-netted by halibut fishermen off California and recently have begun showing up in gillnets set by thresher fishermen off the north-central part of that state, but are presently not considered marketable; most caught incidentally are considered a nuisance due to the damage they do to salmon nets.

The flesh is used fresh for human consumption in Japan where it is processed into various fish products, and to a lesser extent in Alaska and California; its liver oil, skin (for leather) and fins (for shark-fin soup) are also utilized.

Remarks A broad-spectrum predator that occupies a very high trophic level in subarctic waters of the North Pacific, and thus probably plays an important role in stabilizing the marine ecology where it occurs; recently, there has been a major attempt to launch a commercial fishery for this species off Alaska, where it does not appear to be migratory yet the basic life history parameters (population size and structure, recruitment and natural mortality rates, etc.)

necessary for intelligent management of its stocks are poorly known; this seems a recipe for ecologic and economic disaster. Maintaining a warm body in cold seas is a constant battle. It is one of the fundamental facts about the Universe is that, unless substantial energy is expended to combat the trend, heat will always dissipate.

Due to its high heat capacity, water can rob a warm body of heat some twenty times faster than can air at the same temperature. Most sea creatures therefore save considerable energy by simply taking on the temperature of their ambient environment. This strategy conserves calories that can be put to other uses, such as growth and reproduction, but it places strict limitations on where these cold-bodied critters can live. Yet a few types of sharks - including the Great White and a few of its lamnoid relatives - have developed mechanisms for retaining much of their body heat, joining a select number of warm-blooded marine animals that are free to puncture thermal barriers that cold-blooded creatures cannot.

It would be interesting to know what percentage of a Salmon Shark's total caloric budget goes toward stoking its internal fires and how that energy demand impacts its growth and reproductive rate. We do know, however, that the Salmon Shark is widely distributed in cold waters of the North Pacific and an active predator on fast-moving fishes.

The Salmon Shark's range extends from boreal to cool temperate seas of the North Pacific Ocean. In the western part of its range, the Salmon Shark occurs from the subarctic Bering Sea and Sea of Okhotsk south to the Sea of Japan, and in the eastern part from the Gulf of Alaska to southern California and possibly off the seaward side of the Baja Peninsula.

Although it has been taken in waters as warm as 75 degrees Fahrenheit (24 degrees Celsius), the Salmon Shark seems to prefer colder temperatures between 36.5 and 46.5 degrees Fahrenheit (2.5 and 8 degrees Celsius). This species is most common in continental offshore waters, from the surface down to a depth of at least 500 feet (152 metres), but it has been known to come inshore - sometimes just beyond the breaker zone.

In recent years, researchers have noticed that each spring a small number of Salmon Sharks beach themselves in central and southern California. This phenomenon is poorly understood and is being studied. However, the Salmon Shark's ability to maintain a warm body temperature has enabled it to make an active predatory living in even the chilliest waters of the North Pacific.

The Salmon Shark is reputed to be a voracious feeder, but little is known about how much it actually eats during a given period. Salmon Sharks are, of course, named for their dietary predilection — the flesh is often stained salmon red, just like that of its favorite food.

Adult Salmon Sharks apparently migrate in loose groups of 30 to 40 individuals, following schools of Pacific salmon — including Sockeye ( Oncorhynchus nerka ), Pink ( Oncorhynchus gorbusha ), Chum ( Oncorhynchus keta ), and Coho ( Oncorhynchus kisutch) — as they swim along the great arcs of current flowing off the coasts of northern Japan and the Kamchatka peninsula, the Aleutian Island chain, Alaska and British Columbia.

No one, to my knowledge, has ever observed Salmon Sharks actually chase down and eat fish in the wild, but the image of a group of these stubby sharks picking off schools of salmon as they migrate around the North Pacific reminds one of a late-summer mob of children chasing an ice-cream truck.

Other prey species in the northern part of the Salmon Shark's range include Pacific Tomcod ( Microgadus proximus ), Walleye Pollock ( Theragra chalcogramma ), tuna, Chub Mackerel ( Scomber japonicus ), herring, Atka 'Mackerel' ( Pleurogrammus monopterygius —actually a pelagic greenling of the family Hexagrammidae), sculpins, lumpsuckers (identified as Eumicrotremus orbis, but may have been Aptocyclus ventricosus, which is common in the epipelagic layer of the Bering Sea), Longnose Lancetfish ( Alepisaurus ferox ), Daggertooth ( Anotopterus pharao ), and the Spiny Dogfish ( Squalus acanthias ); in southern parts of its range, the Salmon Shark feeds chiefly on squids, lanternfishes (Myctophidae), Pacific Pomfret ( Brama japonica ), and Pacific Saury ( Cololabis saira ).

The Salmon Shark is respectably large, growing to a maximum length of perhaps 12 feet (3.7 metres). Individuals longer than about 5 feet (1.5 metres) have the ventral surface coarsely blotched with black.

Males mature at a length of about 6 feet (1.8 metres) and an age of about 9 to 10 years, females at a length of about 7.2 to 7.5 feet (2.3 to 2.3 m) and an age of about 10 to 11 years.

Like other members of its family (Lamnidae), the Salmon Shark is ovoviviparous and the late-term embryos are oophagous. The gestation period in this species is believed to be somewhat less than a year, but details are lacking.

Usually two to four pups are produced per litter, their length at birth is about 31.5 to 34 inches (80 to 87 centimetres). The young are born in selected nursery areas offering rich feeding and relatively few potential predators. Interestingly, young Salmon Sharks measuring between 43 to 47 inches (110 to 120 centimetres) long do not seem to migrate, possibly to save energy that can then be put toward growth and evasion of predators. To many commercial salmon fisherman, the Salmon Shark is a hated rival. It has been estimated that, each year in the eastern North Pacific, Salmon Sharks take between 12 and 25 percent of the annual salmon run.

In addition to competing with fishermen for salmon, each year Salmon Sharks cause considerable damage to salmon nets and gear. In response, many salmon fishermen do not merely kill the Salmon Sharks they capture incidentally, they torture them.

Some clobber the sharks senseless with baseball bats or hack them to death with axes and knives; others exact revenge by slicing off the tail and dumping the still-living shark overboard, to be set upon by its fellows or slowly starve to death. The life-history of the Salmon Shark is better known than that of most other lamnids, due (in part) to recent investigations into the feasibility of launching a commercial fishery for this species off the coast of Alaska.

The reasoning behind this fishery apparently being, ""If you can't beat 'em, eat 'em!"" I can attest that Salmon Shark meat is delicious, but given the species' low reproductive potential and the boom-and-bust history of shark fisheries in general, it seems unlikely that the Salmon Shark would prove better able to withstand the onslaught of a commercial fishery than other sharks.

Due to its large size, relationship to known dangerous species, and a few unsubstantiated attacks attributed to this species (possibly due to confusion with the White Shark), the Salmon Shark has traditionally been regarded as potentially dangerous.

Recently, however, divers off California have observed and photographed groups of adult Salmon Sharks underwater, with no threatening or aggressive overtures on the part of the sharks. In August 1991, I enjoyed the good fortune of an underwater encounter with a lone, 7-foot (2.2-metre) Salmon Shark off Sandspit, in the Queen Charlotte Islands.

The shark had apparently been lured by our cleaning of pots and pans over the side of the boat. Realising that it was almost certainly a Salmon Shark, and still dressed in my wetsuit from that morning's dive, I quickly grabbed my mask, fins, and some salmon scraps left over from the previous night's dinner, then plunked overboard. The water was bone-shatteringly cold, murky, and green. I swam a few strokes away from the boat, trying desperately to peer through the emerald haze.

There! A flicker of movement in the diffuse half-light. The shark was incredibly beautiful! Faint webs of underwater sunlight danced along its spindle-shaped body and paddle-shaped fins. I studied the shark's proportions, to compare them with illustrations I had seen and confirm its identity. The dorsal fin seemed to be standing at attention, alert. The gills were quite long, extending almost the entire depth of the shark's throat.

My temples throbbed from the cold, it was getting hard to think systematically, and my snorkel-breathing seemed incredibly, terrifyingly loud; I was deeply concerned that the noise might frighten away the shark. In profile, the shark's tail stalk seemed ridiculously slender to power its massive, crescentic and deeply forked caudal fin.

At the other end, the shark's bullet-shaped snout was pocked with large, black, sensitive-seeming eyes. It was a Salmon Shark, all right, probably female. My attention then shifted to the shark's behavior. Its movements were quick and jerky, as though conflicted about whether or not to approach the bait I offered. Try as I might, I could not lure the shark closer than about 25 feet (8 metres) — insufficient to confirm its sex. I had originally attributed the shark's stand-offish behavior to the caution typical of many predatory animals, perhaps compounded by proximity of the boat and the whoops and hollers of my companions back on deck.

But, perhaps due to the mind-numbing cold, I couldn't help thinking that maybe somehow it knew I had recently eaten one of its brethren. As a warm-bodied creature myself, a deep sense of self-preservation forced me to leave the water after being in for only about 8 minutes.

I swam back to my companions' boat and half-climbed, was half-dragged, back on board. It was only then that I noticed that I was white as a parsnip and covered in goose-flesh. Shivering uncontrollably, I endured endless rounds of ""fish food"" jokes and being told, with an odd mixture of utter disbelief and absolute sincerity, that I was ""f**king crazy"". But in a young career already shimmering with scores of precious undersea adventures, I count the experience of swimming with a living Salmon Shark among the most wonderful 8-minutes of my life. Ecology of the Salmon Shark "

Like all extant lamnids, the Porbeagle is warm-bodied, maintaining its internal temperature 12.5 to 18 degrees Fahrenheit (7 to 10 degrees Celsius) higher than the water temperature. It has been known to leap out of the water in pursuit of prey.

Biology of the Porbeagle

"Biology of the Porbeagle ( Lamna nasus)Field Marks Body heavy, spindle-shaped; snout conical and moderately long (distance from tip of snout to eye is about 50% distance from eye to first gill slit); teeth moderately large, blade smooth-edged with basal cusplets; gill slits long, extending partially onto top of head; first dorsal fin originating over axil ('armpit') of pectoral fins and with light free rear tip; second dorsal and anal fins minute, with pivoting bases; strong keels on caudal peduncle (tail stalk), with a short secondary keel on each side of the caudal fin base; caudal fin lunate, with lower lobe almost as long as the upper.

Color: dark bluish grey to brown above, white below in adults, although juveniles often have dusky patches beneath the pectoral fins and around the undersurface of the gill slits. Size Pups are 24-30 in (60-75 cm) long and about 20 lbs (9 kg) in weight at birth; most individuals are 5-6 ft (1.5-1.8 m) long and about 300 lb (135 kg) in weight; maximum recorded length is 9.4 ft (2.9 m), but reported to reach 12 ft (3.7 m) in length and 500 lb (230 kg) in weight; specimens longer than 8 ft (2.5 m) are rare.

Range Amphitemperate in coastal and oceanic regions; apparently does not occur in the North Pacific, where it is replaced by the Salmon Shark ( Lamna ditropis ).

Habitat Common in littoral and epipelagic zones of cold to warm temperate waters; most abundant in cool temperate waters on offshore fishing banks over continental shelves, but also found far from land in ocean basins and occasionally close inshore; a recent record of this species in brackish waters of Mar Chiquita, Argentina. Known depth range from the surface down to at least 2 345 ft (715 m), although most catches occur at depths 180-295 ft (55-90 m); seems to prefer water colder than 64°F (18°C) and has been caught at high latitudes in water as cold as 35°F (2°C); partially endothermic, maintaining its body temperature 12.5-18°F (7-10°C) warmer than ambient.

May come inshore and to the surface during summer months, but tends to stay at depth in offshore waters during winter; fisheries catches in Europe indicate segregation by size and sex.

Feeding Preys on squids and a wide variety of bony and cartilaginous fishes, including pelagic schoolers such as mackerels, pilchards and herrings, various gadoids (cod, hakes, haddock, cusk, and whiting), john dories, flounders, and other sharks such as the Spiny Dogfish ( Squalus acanthias) and Tope ( Galeorhinus galeus ); reported to be active and strong-swimming in pursuit of fish and squid prey, but also takes whelks and sea urchins, suggesting it may sometimes forage at or near the bottom (stomach contents have included stones).

Reproduction Ovoviviparous, featuring oophagy at late stage of development; late-term pups develop grotesquely distended abdomens and branchial (gill) regions. Litter size 1-5, typically 4 (2 per uterus); gestation period in European waters has been estimated to be about 8 months. Breeds on both sides of the North Atlantic: off Europe and the British Isles pregnant individuals are caught during most of the year except July-September; off North America from Massachusetts to Maine, pregnant individuals are caught year-round.

Pups are apparently born in the spring off Europe and late summer off North America; mating in European waters occurs in late summer (September-October), and breeding there probably occurs every year; mating behavior apparently includes the male biting the pectoral fins of females, fresh mating scars occur December-January off Shetland.

Breeding populations almost certainly exist elsewhere in this species' range, but details are lacking.

Age & Growth Males mature at a length of about 5-6.6 ft (1.5-2.0 m), females at 6.6-8.2 ft (2.0-2.5 m), although there is a record of an apparently mature female that was only 5 ft (1.52 m) long; both sexes grow at a similar average rate; age at maturity for both sexes in the North Atlantic has been estimated from vertebral growth rings at 8 yrs.

Longevity for both sexes estimated to be at least 20 yrs. Danger to Humans Regarded as potentially dangerous due to its large size and relationship to known dangerous species, but few people willingly swim in the cold offshore waters it usually inhabits; the SAF currently lists 3 attacks attributed to this species, but these may be due to confusion with the White Shark ( Carcharodon carcharias ).

Has been photographed underwater while hooked on a surface line and made no aggressive overtures toward the diver (apparently more concerned with escape than attack), but little is known of its disposition toward divers.

Utilization Heavily fished and utilized in the North Atlantic and Mediterranean by many countries, including Norway, Denmark, the Faroe Islands, the United Kingdom, France, and previously Spain; a considerable fishery by Japanese longliners exists in the central Indian Ocean and it is often taken as a bycatch by Japanese longliners fishing for Southern Bluefin Tuna ( Thunnus maccoyii) off Tasmania. Its flesh is used fresh and dried salted for human consumption, also used for liver oil, fishmeal, and the fins for shark-fin soup.

Primarily caught with pelagic longlines, but also taken on pelagic and bottom trawls, handlines and gillnets. Classed as a gamefish because it puts up a determined fight, though it does not leap like the Shortfin Mako ( Isurus oxyrinchus ); IGFA all-tackle record is 507 lb (230 kg), caught in Pentland Firth, off Caithmess, Scotland, in March 1993.

Stocks in the North Atlantic show signs of serious over-fishing in the form of greatly declining catches (total weight of catches in 1981 were about 47% those of 1978); IUCN Red List status LT/nt.

Remarks During the 1960's, this species was actively fished off Newfoundland, Canada, by Norwegian fishermen, who took about 9,000,000 lbs (4,100,000 kg) annually, destined for the European food market; this fishery has all but collapsed due to overfishing.

The species is once again fairly common in Canadian Atlantic waters. We humans have a highly developed sense of play. We devote an astonishing amount of our time, resources, and ingenuity toward amusing ourselves. Although we realize that play serves some very serious purposes in our intellectual and social development, mostly we love this class of activity purely and simply because it's fun.

Due to play's undeniable importance to us, we tend to regard with particular favor — and even kinship — those relatively few animals that seem to share our frolicsome predilection.

We regard play as a hallmark of joie de vivre, of high intelligence, of being like us. Dolphins, monkeys, puppies, kittens, and such, hold a special place in our hearts, in part, because they seem to enjoy play as much as we do.

The Porbeagle is among the very few fishes that seem to exhibit play behavior. There have been a few, sporadic accounts — principally from off the Cornish coast — of Porbeagles playing with floating objects, both man-made and natural. Porbeagles have been reported rolling while swimming along the surface, repeatedly wrapping and unwrapping their snouts and forward portion of their bodies in kelp fronds, which often trail behind the shark like rubbery streamers.

Sometimes a Porbeagle thus engaged was observed being chased by other Porbeagles. One could argue, I suppose, that the kelp-rolling sharks were attempting to feed on bryozoans, gastropods, or other tiny organisms living on the kelp, or that they were using the resilient algae to help remove copepod skin parasites (either of which behaviors would be remarkable in its own right).

But such 'pseudo-explanations' seem less-than-compelling. To my mind, such kelp-rolling behavior seems more likely to be exploratory object manipulation or tactile self-stimulation than simple feeding or scratching.

The repetitive nature of this behavior is highly characteristic of what in other mammals would unhesitatingly be termed play. But because the Porbeagle is a 'mere' fish, ethologists are reluctant to use that term. The Porbeagle, of course, doesn't care about such semantic contention, and does what it does for its own reasons.

Such carefree behavior belies the fact that Porbeagles have been subject to much human pursuit and exploitation. This species has long been targeted commercial fishing in European waters and is much sought-after as a sportfish off New England — where they are affectionately known as ""Fakos"", as they are often mistaken by neophytes for the closely related Shortfin Mako ( Isurus oxyrinchus) — and the United Kingdom.

Many English sport anglers are well aware of the Porbeagle's curiosity. These sharks are apparently fascinated by anglers' balloon floats (from which bait is suspended), prodding them repeatedly with the snout and sometimes even trying to bite the soft, spheroid wonders; when a balloon that a Porbeagle was exploring 'pops', the shark typically shakes its head then pauses momentarily, as though it simply cannot believe its eyes (fish just don't do that sort of thing!).

On the other side of the North Atlantic, centered off Nova Scotia, Canada, this same species was nearly wiped out by heavy commercial fishing during the 1960's. At the height of the fishery, Norwegian longliners hauled in some 9 million pounds (4 million kilograms) of Porbeagle annually.

If the average shark caught in this fishery weighed about 300 pounds (135 kilograms) æ surely a generous estimate æ that translates to at least 30 000 individual sharks per year.

Most of this catch was shipped to Italy, where the meat — known as smerglio — is extremely popular: the carcasses are displayed at markets with their sandpapery skins on, so that buyers can be sure that they are not being sold some other, less desirable fish.

Soon the Norwegian Porbeagle catch figures off Nova Scotia began to diminish, demonstrating that a shark population could easily be ""fished out"" in an area where the target species is nonmigratory and has a low reproductive rate. Porbeagles may take five or more years to reach sexual maturity and produce small litters of one to five pups (typically four, two per uterus) per year.

These sharks thus cannot suffer vast depredations on their adult populations without drastic effects. Despite its goofy-sounding name (from the Cornish porbugel, supposedly a combination of porpoise and beagle, referring to its chubby body and determined hunting behavior), the Porbeagle is a first-class predator. Also known as the Mackerel Shark, it feeds primarily on small pelagic schooling fishes, including silvery clouds of mackerels, pilchards, and herrings, as well as drably-garbed bottom-associated fishes such as cods, hakes, cusk, whitings, John Dories, dogfishes, and Tope Sharks ( Galeorhinus galeus ).

It also feeds on squids and — at least occasionally — on the bottom, as whelks and sea urchins have been found as stomach contents. Because of its largish size (to 12 feet or 3.7 metres), the Porbeagle is regarded as potentially dangerous to humans; two attacks on people have been attributed to this species, but may have resulted from confusion with the Shortfin Mako or White Shark ( Carcharodon carcharias ). In any case, most people would not willingly enter the frigid waters inhabited by this shark. The Porbeagle inhabits inshore and offshore cold temperate seas, less than 66 degrees Fahrenheit (19 degrees Celsius), from the surface down to a depth of at least 1,200 feet (366 metres).

Like all extant lamnids, the Porbeagle is warm-bodied, maintaining its internal temperature 12.5 to 18 degrees Fahrenheit (7 to 10 degrees Celsius) higher than the water temperature. It has been known to leap out of the water in pursuit of prey.

With such a high-energy lifestyle, it's a wonder that a Porbeagle would spare any time to investigate or play with novel objects. Even facing the serious business of capturing food for itself and extensive human depredations, the Porbeagle remains as curious and carefree as ever.

Ernest Hemmingway often rhapsodized about the ideal of grace under pressure. Given our long and deep appreciation of play as a pursuit worthwhile for its own sake and our warm admiration (or is that envy?) of the ability of children to play happily no matter what societal horrors and adult stresses are going on about them, it is remarkable that we do not extend the Porbeagle especially high accord.

The world may well be a happier place if we could only learn to play under pressure. "

Gruber: Mackerel sharks, including great whites, makos, threshers, and porbeagles, have a heat-conserving mechanism known as the rete mirabile (""wonderful net""), a structure for warming blood passing over the gills.

"A whitetip cruises the reef edge. Exploding Myths Part 2 (back to Part 1)NOVA: Do sharks make sounds? Gruber: They make hydrodynamic sounds when swerving and accelerating, and they make crunching sounds with their teeth and jaws. But they don't have special organs for sound production and apparently don't communicate with sound.

NOVA: Sharks have an endless supply of teeth? Gruber: Yes, and they are unique in this way, too. They produce teeth continuously. Their teeth are not set in sockets like those of other vertebrates but rather loosely and flexibly attached by tendons to their jaws. If they didn't replace teeth continuously—up to 50,000 in a lifetime—their teeth would fall out. That is why shark teeth are the most abundant vertebrate fossil material on the Earth and in the sea.

Scalloped hammerhead on the reef. NOVA: Do sharks have to keep swimming to breathe? Gruber: Several species do, including hammerheads and mackerel sharks. Typically, pelagic sharks that never encounter the bottom are adapted to swim all their lives. But the vast majority of sharks have a buccal (mouth) pump and are not so-called ""obligate ram ventilators.""

(Ram ventilators like hammerheads and great whites must swim to pass water over their gills.) So the answer is no, emphatically. There are even some sharks with spiracles, holes on the top of their head that allow water to enter their gill chambers when the mouth is on the bottom.

Mouth of a hammer. NOVA: Do sharks have to roll over to bite? Gruber: No way, Jose! Sharks have a unique, loose jaw suspension that allows them to raise their snout and loosen their jaw from the braincase, thrusting it forward so that, in effect, the shark has a terminal mouth right out there at the end.

But in reality, sharks rarely bite pieces out of a prey. Usually, they engulf them with their amazing buccal or mouth pump, which acts like a slurp gun. Great white shark NOVA: Are sharks warm-blooded?

Whites can keep their core temperature up to 15°F above ambient seawater. Cocos whitetip and lobster. NOVA: Are sharks insensitive to pain? Gruber: Hard to say, because we don't know what pain means to an animal and can hardly describe it ourselves.

Some people are almost insensitive to pain, others are highly sensitive. I have done minor surgery on sharks, and they seem not to feel it. On the other hand, using what is clearly aversive conditioning I was able to train sharks, showing that they do respond to pain, which can be used as a conditioned stimulus—and a powerful one. So yes, sharks feel something we would call pain. Continue: Can sharks survive finning? "

ce The Largest Great White Sharks Great white sharks ( Carcharodon carcharias) are huge and powerful warm-blooded fish that have been around for at least 11 million years. Also known as white pointers, their ancestors existed on Earth 400 million years ago, which is 200 million years before the first dinosaur appeared.

What Are the Biggest Great White Sharks Ever Recorded?

"Owlcation » STEM » Marine Biology What Are the Biggest Great White Sharks Ever Recorded? Updated on July 8, 2015sharkfacts more Contact Author Sour

This fearsome predator at the top of the oceanic food chain has long commanded man’s fascination and respect. Though the great white isn’t the biggest shark in the world (that title goes to the whale shark), it is the largest predatory fish, growing up to 20 feet long and weighing a massive 5000 pounds.

Females are bigger than males. Female adults reach an average length of 16', while adult males reach 12'. Every now and then we hear reports of great whites that reach even greater lengths. The Biggest One Ever Found? A Harder Question Than It Seems So what is the biggest great white shark ever found? Well, the answer to that question is not so simple.

First of all, most sharks are caught by fishermen, and we all know how truthful they can be at times—I swear it was this big!—when all they caught was a tiddler. There are also some problems with measuring and estimation that can make finding reliable data difficult.

According to the Guinness Book of Records, the two largest great white sharks ever found were 36' and 37' feet long. The 36' foot shark was captured off Port Fairy in South Australia in the 1870s, while the 37' shark was caught in New Brunswick, Canada, in the 1930s.

However, since those sizes are so abnormal for great whites, experts have cast doubt on the reliability of those measurements, or if they were even great whites at all.

Three of the Biggest Great Whites Ever Caught (and Reliably Measured)According to shark expert J. E. Randall, the largest white shark reliably measured was 6.0 m (19.7 ft), found near Ledge Point, Western Australia in 1987. In 1988, David Mc Kendrick of Alberton, Prince Edward Island, caught a female of similar length: 6.1 m (20 ft) long.

There is also a report of a great white shark found in 1945 in Cuba. This specimen was 6.4 m (21 ft) long and had a body mass of about 3,324 kg (7,328 lb). The length has been verified by shark experts Ellis and Mc Cosker. Great white shark | Source Just How Big Is a 20' Great White Shark?

Imagine a 20-foot great white. If like me you are five feet tall then the shark is four times your length.

A 20-foot shark will be about 6 feet tall, so even if you were swimming upright beside it, it would tower over you. Even more frightening, if you met it face-to-face, its jaws would be 8 feet wide. Eeek! At that size it could easily swallow you whole!Some of the Biggest Great White Sharks Found in the Last Century There have been many tales throughout the years of people finding huge great white sharks.

With photographic evidence, it’s been possible for experts to prove or disprove the claims. Here are some of the most well-known findings (in addition to the ones above): In 1983, Canadian David Mc Kendrick caught a 20.3 ft (6.1 m) great white shark at Prince Edward Island.

This length has been verified by the Canadian Shark Research Centre. In 1987, Alfredo Cutajar caught a big great white off the coast of Malta that was reportedly measured to be 7.13 meters long. There’s been some dispute about the accuracy of the number, however, and experts have been arguing over it for years.

Shark experts Richard Ellis and John E. Mc Cosker, authors of the book The Great White Shark (1991), have also largely discounted the claim of the Maltese fisherman. On May 14, 1997, a great white shark was caught in a set-net in Seven Star Lake, Hualien County, Taiwan. Its length was estimated to be between 6.7 and 7.0 meters, which is between 22 and 23 feet but its length has not been verified.

In 2009, a massive male great white shark was caught off Guadalupe Island, Mexico, measuring 17.9 feet (5.5 m). He was then tagged and released, allowing scientists to track his future movements. In April 2012, two Mexican fishermen caught more than they bargained for in their nets—a 2000 lb dead great white shark.

It took more than 50 men to drag the shark from the shore to the docks, where it was later cut up and served to the townsfolk to eat.dead great white shark, Mexico, 2012.

| Source The Largest Sharks Ever Caught Date Length Verified? Location1870s 36 ft / 10.97 m No Port Fairy, South Australia1930s 37 ft / 11.27 m No New Brunswick, Canada1945 21.3 ft / 6.49 No Cuba1983 20.3 ft / 6.1 m Yes Prince Edward Island, Canada1987 19.7 ft / 6.0 m Yes Ledge Point, Western Australia1987 24 ft / 7.13 m No Malta1988 20 ft / 6.1 m Yes Alberton, Prince Edward Island199722 - 23 ft / 6.7 or 7 m No Seven Star Lake, Hualien County, Taiwan2009 17.9 ft / 5.5 m Yes Guadalupe Island, Mexico2012 (2000 lb shark - no length provided)No Mexico One of the Biggest Great Whites Ever Filmed One of the Biggest Great Whites Ever Filmed | Jaws Strikes Back Your browser does not currently recognize any of the video formats available.

Click here to visit our frequently asked questions about HTML5 video.0:00 / 2:00Why It’s Hard to Measure Great White Sharks Maybe you’re wondering why it’s so difficult to come up with reliable shark measurements.

Measuring great white sharks is difficult for a couple of reasons: It’s dangerous to be near them in water. They’ve not been successfully bred in captivity (for some reason they do not thrive away from the ocean).

They shrink out of the water, so the initial size might change by the time scientific investigators are on the scene to measure. It’s difficult to get good measurements while the fish are swimming. They are difficult to catch and land.

Great white sharks are protected in many oceans of the world and cannot be killed at random. Dead great white sharks are eaten at sea by other sharks, and their carcasses rarely wash up on the beach. That said, programs are now underway to tag smaller specimens, and as they grow, scientists will be able to take readings from those tags since they are linked up to satellites.

Hopefully in the future man can learn much more about this amazing beast. Vic Hislop with his family | Source One Shark Hunter’s Opinion Edit International, a site run by Ron Laytner, has a very interesting article from 2011 in which Laytner discusses discusses Vic Hislop, an Australian on a mission to hunt sharks.

A man with unconventional views, Vic Hislop was 60 years old at the time of the article, with over 40 years of experience of hunting down and killing great white sharks.

He believes that many more people are eaten by the great white than is being reported. He accuses the Australian government of masking many shark attacks by recording their deaths as drowning in order to protect tourism. Hislop says:""At least a hundred swimmers disappear every year here and their bodies are never found.

Many have been eaten. I’ve often caught sharks and removed human hands and feet from their stomachs. I even found a human foot still in its sandal. """"There Are Bigger Sharks Out There""Mr Hislop also believes there are even bigger sharks out there in our oceans, as he has witnessed many great whites 20' or more with bite marks on their bodies, suggestive of even bigger sharks.

He believes great white sharks can develop a taste for humans, and that once one does, it will travel from beach to beach devouring humans whenever it feels hungry. Since sharks swallow their prey whole, killing a shark that has eaten a human will allow the remains to be recovered. But current shark protection measures prohibit such killing, which Hislop believes denies closure to families who have lost loved ones.

Are We Teaching Sharks to Hunt Humans? Shark nets, put in place to protect beaches, become fast-food snack bars for great whites, who eat the dolphins and stingrays trapped by the nets. According to Hislop while eating their prey, the sharks bite through the nets and then simply swim through to reach the shore. Therefore, shark nets actually attract great whites, bringing them closer to the people the nets were put there to protect. Hislop says humans are contributing to the man-eating shark problem in other ways. When Australian filmmakers fill wetsuits with fish to try to get the best great white shark attack shot, they teach the great white to associate divers with food. Finally, commercial fishing is wiping out sharks’ natural food, fish, bringing them inshore to find a new diet: human. Hislop has one last tip: punching a great white to try and deter an attack is a waste of time. Punching a creature with thick skin like rough sandpaper will only injure your knuckles. "

For many people, sharks are the epitome of the 'cold-blooded killer'. The warm-bodied mackerel sharks are spectacular reminders that many of our stereotypes are inaccurate. As apex predators, sharks are absolutely essential to the health and vigor of marine ecosystems.

Fire in the Belly of the Beast

"Fire in the Belly of the Beast White Shark ( Carcharodon carcharias)Right now you are burning. Your body is busily oxidizing your last meal, converting it into new tissue, energy, and heat. This internal combustion is a 'slow burn', but the result is the same as a roaring bonfire: carbon compounds are combined with oxygen, breaking them down and producing thermal energy in the process.

The greater the difference between the temperature inside and outside your body, the more rapidly you radiate this heat to the environment. The body temperature of most creatures — including insects, fishes, and reptiles — fluctuates with the temperature of their environment. This is known as ' ectothermy ' or 'cold-bloodedness'. Because they cannot maintain a constant body temperature, cold-blooded creatures tend to live where the average environmental temperature is optimal for them.

But birds and mammals are able to physiologically regulate their internal temperature within a narrow, optimal range. This is called ' endothermy ' or 'warm-bloodedness'. Our warm-bloodedness has (in part) enabled our species to extend its range from the warm equatorial tropics where we evolved to the cold temperate zones of higher latitudes.

In cold environments, we can use insulation to help maintain our bodies' internal temperatures. Water conducts heat many times faster than air, draining precious body heat with unrelenting efficiency. When diving, we rely on our dry or wet suits to insulate us against heat loss by trapping a layer of warm air or water against our skin.

If we venture into a cold aquatic environment without such insulation, our internal thermostats need to work overtime to prevent hypothermia. I'm sure you will agree it is much easier (and more comfortable!) to swim in warm water than to warm cold water with your body heat. Many types of marine animal — including most sharks — are ectothermic, and thus are most abundant in warm waters.

But at least seven species of mackerel sharks — the Great White ( Carcharodon carcharias ), the Longfin ( Isurus paucus) and Shortfin ( Isurus oxyrinchus) makos, the Porbeagle ( Lamna nasus) and Salmon Shark ( Lamna ditropis ), the Common Thresher ( Alopias vulpinus) and the Bigeye Thresher ( Alopias superciliosus) — have successfully invaded cold wate

rs. These sharks are unique in their ability to elevate and maintain body temperatures as much as 13 °C above the ambient water temperature. One striking feature of these warm-bodied sharks is that their flanks and viscera are warm, while the heart and gills are at environmental temperatures.

This is because they differ substantially from all other sharks in the pattern of blood supply to the viscera and swimming muscles. The warm-bodied mackerel sharks have a special organ in their circulatory systems, allowing them to retain much of the heat generated by swimming and muscular activity.

In cold-bodied sharks, this heat is radiated from the body surface and lost to the environment. Warm-bodied sharks are able to greatly reduce this heat loss by redirecting blood from enlarged arteries along the flanks inward through a dense bundle of small arteries and veins called the rete mirable (or ""wonderful net""). The arteries in each rete carry cold, oxygenated blood from the gills, while the veins carry metabolically-warmed, deoxygenated blood. These small arteries and veins pass very close to one another, carrying blood in opposite directions. Because of this intimate countercurrent blood flow, most of the heat is transferred from the veins to the arteries and cycled back to the muscles and visceral organs that produced it originally.

The warm-bodied mackerel sharks have three sets of retia: one in the swimming muscles, another in the anterior viscera, and a third surrounding the brain. Mackerel sharks with this modified circulatory system are able to maintain body temperatures well above that of the water in which they swim.

The advantages of being warm-bodied are stupendous. A 10 °C rise in body temperature can result in a three-fold increase in the speed and strength of muscle contraction — providing more power from a given muscle mass. For mackerel sharks, this may afford an increase in sustained swimming speeds. Greater speeds may be selectively advantageous when chasing prey or fleeing from predators (although it is difficult to imagine anything — other than man — regularly preying on even moderately large mackerel sharks) Being warm-bodied might also allow mackerel sharks to make excursions into colder or deeper waters.

To remain alert in the mind-numbing chill, mackerel sharks have a rete ' brain heater ' to help stave off the grogginess brought on by their cold-water environment.

Theoretically, conservation of body heat may allow a more complete conversion of heat energy to work — or, to put it informally, more miles-per-fish. Elevated visceral temperatures — which are highest in the intestinal valve — may increase the rate of digestion and absorption of food, making available more caloric energy per day.

The visceral retia also warm the uteri. By holding their young in warm uteri, mackerel sharks may somehow enhance the development of their embryos. Perhaps this shortens gestation, increasing the number of pregnancies a warm-bodied shark may have over her lifetime. Unfortunately, we know so little about development in these sharks that their gestation periods cannot be compared with those of cold-bodied sharks.

But the advantages of endothermy are costly. To maintain a warm body in cold water, a mackerel shark must burn fuel like a blast furnace. A warm-bodied shark may need more than ten times as much food as a cold-bodied shark of the same size.

The thin biomass of tropical seas cannot readily support such high-energy carnivores. Since large fishes and large, energy-rich marine mammals tend to live inshore in cold temperate waters, mackerel sharks are most abundant in these areas.

The distribution of warm-bodied sharks is thus dictated largely by availability of prey. For example, the Great White Shark is undeniably one of the sea's paramount predators: it can — and does — feed on virtually anything that swims.

Adult White Sharks feed heavily upon seals and sea lions, which are large, swift, and agile. Most pinniped rookeries (large breeding colonies) are in cold temperate or sub-polar regions, and the white shark rarely strays far from these important food sources. Although the White Shark ( Carcharodon carcharias) regularly visits warm and even tropical waters, it is primarily an inhabitant of cool temperate seas. Its ability to exploit the rich feeding in these productively rich waters is made possible by a combination of a specialized heat-retaining circulation and sheer bodily bulk.

Photo © David Fleetham david@davidfleetham.com ; used with the gracious permission of the photographer. While energetically expensive, endothermy has enabled the mackerel sharks to function as effective predators in cold waters, taking advantage of the rich feeding available there.

In the North Atlantic, Shortfin Makos pursue high-speed ocean rovers, such as bluefish and swordfish. The Salmon Shark is an endurance predator, picking off Pacific salmon as they migrate along the coasts of Alaska and northern Japan. The Bigeye Thresher swims deep in cold water, scanning the surface for the silhouette of schooling baitfish with its huge, upward-mounted eyes.

The combination of large size, efficient metabolism, high-speed swimming, and powerful jaws help make the mackerel sharks versatile predators, allowing them to feed on a broad spectrum of prey types. By extending their range into cold waters, these sharks avoid competition with their cold-bodied cousins, which must remain in warmer seas.

No doubt the heat-retaining retia of the mackerel sharks have freed them from being captives of the isotherms — allowing them to range throughout the breadth and depths of the World Ocean.

For many people, sharks are the epitome of the 'cold-blooded killer'. The warm-bodied mackerel sharks are spectacular reminders that many of our stereotypes are inaccurate. As apex predators, sharks are absolutely essential to the health and vigor of marine ecosystems.

Fire in the Belly of the Beast

But birds and mammals are able to physiologically regulate their internal temperature within a narrow, optimal range. This is called ' endothermy ' or 'warm-bloodedness'. Our warm-bloodedness has (in part) enabled our species to extend its range from the warm equatorial tropics where we evolved to the cold temperate zones of higher latitudes.

In cold environments, we can use insulation to help maintain our bodies' internal temperatures. Water conducts heat many times faster than air, draining precious body heat with unrelenting efficiency. When diving, we rely on our dry or wet suits to insulate us against heat loss by trapping a layer of warm air or water against our skin.

But at least seven species of mackerel sharks — the Great White ( Carcharodon carcharias ), the Longfin ( Isurus paucus) and Shortfin ( Isurus oxyrinchus) makos, the Porbeagle ( Lamna nasus) and Salmon Shark ( Lamna ditropis ), the Common Thresher ( Alopias vulpinus) and the Bigeye Thresher ( Alopias superciliosus) — have successfully invaded cold wate

rs. These sharks are unique in their ability to elevate and maintain body temperatures as much as 13 °C above the ambient water temperature. One striking feature of these warm-bodied sharks is that their flanks and viscera are warm, while the heart and gills are at environmental temperatures.

This is because they differ substantially from all other sharks in the pattern of blood supply to the viscera and swimming muscles. The warm-bodied mackerel sharks have a special organ in their circulatory systems, allowing them to retain much of the heat generated by swimming and muscular activity.

The warm-bodied mackerel sharks have three sets of retia: one in the swimming muscles, another in the anterior viscera, and a third surrounding the brain. Mackerel sharks with this modified circulatory system are able to maintain body temperatures well above that of the water in which they swim.

To remain alert in the mind-numbing chill, mackerel sharks have a rete ' brain heater ' to help stave off the grogginess brought on by their cold-water environment.

Theoretically, conservation of body heat may allow a more complete conversion of heat energy to work — or, to put it informally, more miles-per-fish. Elevated visceral temperatures — which are highest in the intestinal valve — may increase the rate of digestion and absorption of food, making available more caloric energy per day.

But the advantages of endothermy are costly. To maintain a warm body in cold water, a mackerel shark must burn fuel like a blast furnace. A warm-bodied shark may need more than ten times as much food as a cold-bodied shark of the same size.

The thin biomass of tropical seas cannot readily support such high-energy carnivores. Since large fishes and large, energy-rich marine mammals tend to live inshore in cold temperate waters, mackerel sharks are most abundant in these areas.

The distribution of warm-bodied sharks is thus dictated largely by availability of prey. For example, the Great White Shark is undeniably one of the sea's paramount predators: it can — and does — feed on virtually anything that swims.

Photo © David Fleetham david@davidfleetham.com ; used with the gracious permission of the photographer. While energetically expensive, endothermy has enabled the mackerel sharks to function as effective predators in cold waters, taking advantage of the rich feeding available there.

In the North Atlantic, Shortfin Makos pursue high-speed ocean rovers, such as bluefish and swordfish. The Salmon Shark is an endurance predator, picking off Pacific salmon as they migrate along the coasts of Alaska and northern Japan. The Bigeye Thresher swims deep in cold water, scanning the surface for the silhouette of schooling baitfish with its huge, upward-mounted eyes.

The combination of large size, efficient metabolism, high-speed swimming, and powerful jaws help make the mackerel sharks versatile predators, allowing them to feed on a broad spectrum of prey types. By extending their range into cold waters, these sharks avoid competition with their cold-bodied cousins, which must remain in warmer seas.

No doubt the heat-retaining retia of the mackerel sharks have freed them from being captives of the isotherms — allowing them to range throughout the breadth and depths of the World Ocean.

For many people, sharks are the epitome of the 'cold-blooded killer'. The warm-bodied mackerel sharks are spectacular reminders that many of our stereotypes are inaccurate. As apex predators, sharks are absolutely essential to the health and vigor of marine ecosystems.

rs. These sharks are unique in their ability to elevate and maintain body temperatures as much as 13 °C above the ambient water temperature. One striking feature of these warm-bodied sharks is that their flanks and viscera are warm, while the heart and gills are at environmental temperatures.

Fire in the Belly of the Beast

But birds and mammals are able to physiologically regulate their internal temperature within a narrow, optimal range. This is called ' endothermy ' or 'warm-bloodedness'. Our warm-bloodedness has (in part) enabled our species to extend its range from the warm equatorial tropics where we evolved to the cold temperate zones of higher latitudes.

In cold environments, we can use insulation to help maintain our bodies' internal temperatures. Water conducts heat many times faster than air, draining precious body heat with unrelenting efficiency. When diving, we rely on our dry or wet suits to insulate us against heat loss by trapping a layer of warm air or water against our skin.

But at least seven species of mackerel sharks — the Great White ( Carcharodon carcharias ), the Longfin ( Isurus paucus) and Shortfin ( Isurus oxyrinchus) makos, the Porbeagle ( Lamna nasus) and Salmon Shark ( Lamna ditropis ), the Common Thresher ( Alopias vulpinus) and the Bigeye Thresher ( Alopias superciliosus) — have successfully invaded cold wate

This is because they differ substantially from all other sharks in the pattern of blood supply to the viscera and swimming muscles. The warm-bodied mackerel sharks have a special organ in their circulatory systems, allowing them to retain much of the heat generated by swimming and muscular activity.

The warm-bodied mackerel sharks have three sets of retia: one in the swimming muscles, another in the anterior viscera, and a third surrounding the brain. Mackerel sharks with this modified circulatory system are able to maintain body temperatures well above that of the water in which they swim.

To remain alert in the mind-numbing chill, mackerel sharks have a rete ' brain heater ' to help stave off the grogginess brought on by their cold-water environment.

Theoretically, conservation of body heat may allow a more complete conversion of heat energy to work — or, to put it informally, more miles-per-fish. Elevated visceral temperatures — which are highest in the intestinal valve — may increase the rate of digestion and absorption of food, making available more caloric energy per day.

But the advantages of endothermy are costly. To maintain a warm body in cold water, a mackerel shark must burn fuel like a blast furnace. A warm-bodied shark may need more than ten times as much food as a cold-bodied shark of the same size.

The thin biomass of tropical seas cannot readily support such high-energy carnivores. Since large fishes and large, energy-rich marine mammals tend to live inshore in cold temperate waters, mackerel sharks are most abundant in these areas.

The distribution of warm-bodied sharks is thus dictated largely by availability of prey. For example, the Great White Shark is undeniably one of the sea's paramount predators: it can — and does — feed on virtually anything that swims.

Photo © David Fleetham david@davidfleetham.com ; used with the gracious permission of the photographer. While energetically expensive, endothermy has enabled the mackerel sharks to function as effective predators in cold waters, taking advantage of the rich feeding available there.

In the North Atlantic, Shortfin Makos pursue high-speed ocean rovers, such as bluefish and swordfish. The Salmon Shark is an endurance predator, picking off Pacific salmon as they migrate along the coasts of Alaska and northern Japan. The Bigeye Thresher swims deep in cold water, scanning the surface for the silhouette of schooling baitfish with its huge, upward-mounted eyes.

The combination of large size, efficient metabolism, high-speed swimming, and powerful jaws help make the mackerel sharks versatile predators, allowing them to feed on a broad spectrum of prey types. By extending their range into cold waters, these sharks avoid competition with their cold-bodied cousins, which must remain in warmer seas.

No doubt the heat-retaining retia of the mackerel sharks have freed them from being captives of the isotherms — allowing them to range throughout the breadth and depths of the World Ocean.

For many people, sharks are the epitome of the 'cold-blooded killer'. The warm-bodied mackerel sharks are spectacular reminders that many of our stereotypes are inaccurate. As apex predators, sharks are absolutely essential to the health and vigor of marine ecosystems.