Sharks: Characteristics, Senses and Movement

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Sharks fishermen are not supposed to catch in the Atlantic Ocean, Gulf of Mexico and Caribbean Sea

Sharks are mostly predatory fish and first rate hunters. They eat almost every creature found in the seas but face few predators themselves as adults other than humans. They are found mostly in tropical and temperate seas but can be found in all marine environments, even polar oceans and deep-sea trenches as well as some freshwater tropical rivers and lakes. Some are flat and look like rays, some have whiskers and beards. Several species glow in the dark. [Sources: Steve Kemper, Smithsonian, August 2005; Eugenie Clark, National Geographic August 1981; Nathaniel Kenney, National Geographic, February 1968; Michael Lemonick, Time, September 1, 1997; Richard Conniff, Smithsonian]

Clearly people have a fascination with sharks as judged by the success of films like “Jaws” and a “Shark’s Tale” and the number of people that tune into the Discovery Channel’s "Shark Week." "Shark Week" is cable's longest-running programming event. It attracted 30.8 million viewers in 2010. Explaining mankind's fascination with them the eminent Harvard biologist E.O. Wilson once wrote: "We're not just afraid of predators, we're transfixed by them, prone to weave stories and fables and chatter endlessly about the them, because fascination creates preparedness and preparedness, survival. In a deeply tribal sense, we love our monsters."

Very little is known about sharks, even basics things like how long they live, where they live, if they are territorial, how many offspring they produce., how many times they can mate in an hour. We do know they grow slowly and some species take more than 20 years to mature. The age of many sharks can be determined by counting the number of growth rings that develop on their vertebrae, with each band representing approximately one year of life.

Websites and Resources: Shark Foundation ; International Shark Attack Files, Florida Museum of Natural History, University of Florida ; Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal ; Woods Hole Oceanographic Institute ; Cousteau Society ; Monterey Bay Aquarium ; MarineBio

Cartilaginous Fishes

20120518-bull shark i_-_Carcharhinus_leucas.jpg
bull shark
Sharks, rays and a group of deep-water fish called chimaeras and their relatives are cartilaginous fish (Chondrichthyes), that have skeletons primarily composed of cartilage as opposed to bony fish (Osteichthyes), the classification most fish fall into. All cartilaginous fish possess skeletons made of cartilage rather than bone and specialized teeth that can be replaced throughout their lives. Some have cartilage strengthened by mineral deposits and bonelike dorsal spines. Bony fishes have skeletons primarily composed of bone tissue.

Chondrichthyes are jawed vertebrates with paired fins, paired nares (nostrils), scales, and a heart with its chambers in series. They range in size from the 10 centimeters (3.9 inch) finless sleeper rays to the 10 meter (32 foot) whale sharks. The class is divided into two subclasses: Elasmobranchii (sharks, rays, skates, and sawfish) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class).or elasmobranch,

Cartilaginous skeletons are much lighter and more flexible than bony skeletons. On the land they would be unable to support the weight of large animals but in water they are effective for animals up to 40 feet in length. Most have skin covered by thousands, even millions, of interlocking scales called dermal denticles. They have a similar composition to teeth and give skin a sandpaper-like texture, increase durability and reduce drag.

Cartilaginous fish have five to seven pairs of gills. When water enters the mouth the gill slits are closed. When waters passes through the open gills the mouth is closed. These fish also lack the swim bladder that give bony fish their buoyancy and instead have an oil-rich liver that adds to their buoyancy. Even so many are negatively buoyant and need to swim to stay afloat.

All cartilaginous fish have a sensory system of pores called ampullae of Lorenzini, named after an Italian biologist who discovered them in 1678, that send out electrical signals that can be used to locate prey and avoid predators. Most also have an effective lateral line system running from their tail to their snout that helps them detect small vibrations.

All cartilaginous fish are carnivorous but for some this means they feed primarily on zooplankton. Most feed on live prey but will feed on carrion if it is available. Few feed exclusively on carrion. Reproduction take place internally when the male passes sperm into the female’s cloaca with a modified pelvic fin. Some species release embryos in leathery egg cases. Other species give birth to live young that hatched from eggs that broke open inside the female. In yet others, embryos develop in placenta-like structures. In all cases the young do not go through a larval stage like many bony fish; instead they are born as miniature adults.

Shark Orders

Shark Characteristics

Sharks are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (having a body temperature that fluctuates with the surrounding environment) and have bilateral symmetry (both sides of the animal are the same). Sexual Dimorphism (differences between males and females) occurs but usually is not really obvious. Sometimes males are larger than females. Other times the opposite is true. [Source: Animal Diversity Web (ADW) /=]

Sharks breath through their mouths and most have five pairs of gills, although some have six or seven. Water enters the shark’s body through their mouths and passes over their gills and exist the body through the gill slits. Sharks have gill slits that open directly to the sea and have no covers. Some species of shark can stick their intestines out through their anus and pull them back in again to get rid of small objects.

Sharks jaws are made of cartilage rather bone and contain rows of razor sharp teeth embedded in an elastic dental ligament that carries teeth forward in a conveyor-belt-like fashion from the back of the mouth toward the lip. In most species the front teeth grip and bite while the others stay out of the way until they are reach the front of the mouth.

Sharks have unmistakable sleek bodies. Different shark species often have different number of vertebrae. Shark scientists often use vertebrae counts to distinguish among species. According to Animal Diversity Web: Key physical features include the anal fin, five gill slits, and a mouth positioned behind the eyes and underneath the snout. Some sharks appear grey from a distance, but show a bronze tint when viewed up close. They often have a white underside. Males are distinguished by the elongate mating claspers on their pelvic fins. /=\

According to the New York Times: Scales cover the bodies — and even the eyeballs — of sharks. Known as “dermal denticles,” the scales function like protective armor and their ridges also reduce drag as the animals swim. The scales are microscopic — each one is only about the width of a human hair — but sharks slough off about 100 denticles for each tooth they lose, making them common in the fossil record. This abundance makes them valuable to scientists seeking to understand the past. [Source: Katherine Kornei, New York Times, June 4, 2021]

Shark Teeth — a New Set Every 10 Days

Some shark species have more than 20 rows of teeth. As front row teeth break or wear down they are replaced by newer, younger teeth. The elastic ligaments allows the teeth to wiggle slightly to fit around bone or skip over hard parts of prey. Even species that are hundreds of millions of old have these replaceable rows.

Teeth are adapted to suit the prey that sharks feed on. Serrated teeth are used for cutting while pointed teeth are designed to grip prey. Shark jaws are normally located under the brain case so that when a shark approaches prey it can lift its snout, allowing the upper jaw to slide forward and the lower one to drop. When fully open, muscle contractions the jaws away from the braincase, giving the shark a better grip.

In a “tiny miracle of celular engineering” shark teeth start as a lump of tissue that becomes defined by a network of fibers and then is filled by a bone-like material and covered in a hard seal of enamel. Gareth J. Fraser of the University of Sheffield wrote: Sharks are the ultimate predators of the aquatic realm thanks to one character in particular — teeth. Not only are shark’s teeth razor sharp but they are also constantly regrown throughout life, gradually replaced like a conveyor belt of rows of teeth, and not just when they are worn down or fall out. [Source: Gareth J. Fraser, Lecturer in Evolutionary Developmental Biology, University of Sheffield, The Conversation, August 5, 2016]

“Sharks don’t actually regrow teeth one by one but have multiple rows inside their jaw that are constantly regrown. When a tooth on the edge of the jaw drops out, the corresponding tooth in the row behind it moves forward to replace it. The underlying soft tissues anchor and carry each tooth like a conveyor belt. When juvenile sharks emerge from their egg cases or their mothers’ wombs (sharks can be born either way), they have a fully developed conveyor-belt set of teeth (dentition), with rows of sharp teeth ready for feeding.

My colleagues and I studied the key genes involved in tooth regeneration in a small species of shark known as the catshark (Scyliorhinus canicula). Its eggs can easily be collected and the embryos inside can be raised to show us the precise set of developmental stages that tooth formation and regeneration goes through. We found that within the epithelial cells that line sharks’ mouths there are special compartments of stem cells that are key to the their continuous tooth regrowth. Without these stem cells, the sharks would suffer like humans with only a restricted set of teeth, which would in turn affect their success as hunters at the top of the food chain. We analysed the stem cell compartments in shark’s mouths and deciphered all the active genes involved in shark tooth development and regeneration.

teeth of different sharks

All vertebrate teeth, from sharks to mammals, are incredibly similar. For one thing, their structure is always composed of a hard mineral tissue known as dentine that is covered with even harder enamel or a similar material. But we have also found that the genes that control the process of tooth development are also very similar. This is important because it suggests that the key genetic information that we discover in sharks could be crucial to understanding how tooth regeneration works and how that process is prevented in humans.

Shark Cartilage and Skin

Sharks have no bones; their bodies are held together with cartilage, a gristly substance, softer and more resilient than bone. It consists primarily of a mesh of collagen fibers embedded in a gelatin-like matrix, along with a scattering of cartilage-generating cells called chindrocytes. Cartilage is strong and flexible. Humans have it in their nose and ears.

Sometimes the cartilage is surrounded by a thin layer of mineralized tissue that gives it a little extra stiffness. The cartilage grows and produces rings like those on a tree, which scientist are learning to use to determine the age of sharks.

Shark skin is covered with a protective layer of microscopic, toothlike scales called denticles. Like their teeth, they are pointed, covered in enamel and contain nerves. Shark skin feels like sandpaper and is as tough as leather and as thick as a watermelon rind and can be shed and regrown very quickly. Vicious wounds on a shark that would necessitate an amputation on a human heal in less than three weeks.

Shark red and white locomotor muscles — Lateral view of shark red locomotor muscles (RM) and white locomotor muscles (WM), along with dorsal hollow nerve cord, notochord, pharyngeal gill slits, spiracle, nostril, and eye. B. Transverse cut of a shark showing RM and WM locations
Red locomotive muscle is mainly used for moderate swimming at low speeds while the white locomotive muscles are used for emergencies such as attack, escape or jumping.

Shark denticles reduce drag and increase speed. Shark researcher George Burgess told National Geographic, water “races through the microgrooves without tumbling. Its like a fast-moving river current versus the gurgling turbulence of a shallow stream. Sharks denticles were an inspiration and model for the design of Speedo’s fastskin LZR racer bathing suits that broke a number of world record before and during the Olympics in Beijing in 2008. The scales also discourage barnacles and algae from adhering to the skin and have been an inspiration for synthetic coatings that are being considered for Navy ships to reduce biofouling.

Shark Movement

Sharks are very good swimmers. Their bodies are so hydrothermically streamlined and smooth that water slips off it. They move through the water using the "sinuous motion of the rear half of their bodies and powerful thrash of their tails." The thrust propels the body downwards. The pectoral fins spread horizontally and help sharks maintain stability, sort of like the vanes on a submarine. The top speed of a blue shark is about 30 miles per hour.

Sharks don't have the air-filled swim bladders that keep most species of fish buoyant. They have an oil-filled liver that serves the same purpose to some degree but not as effectively. Since the cartilage-filled bodies of sharks are heavier than water they sink if they stop moving. At one time it was thought that sharks had to keep moving to keep water going through their gills or else they died from lack of oxygen. Although this is largely true sleeping sharks observed near Japan and Mexico have dispelled the misconception that this is true with all sharks.

A shark can not swivel the stiff stabilizing fins behind its head. This means a shark cannot move them into a vertical position to brake and is unable to hoover in one position or swim in reverse like many fish. A charging shark can not stop. It has to move to one side. Unlike the flexible fins of bony fishes the rigid fins possessed by sharks can not be flexed or folded. Their primary job is stabilizing, steering and propelling a shark.

Fast Sharks

A research team led by Yuki Watanabe, an associate professor of marine zoology at the National Institute of Polar Research, compared the long-distance cruising speeds of 46 species of fish. in a paper published in April 2016 on the Proceedings of the U.S. National Academy of Sciences. It showed that a 428-kilogram great white shark swam the fastest at 8.1 kilometers per hour (kph (5 miles per hour (mph)), followed by a 240-kilogram bluefin tuna at 7.2 kph (3.5 mph). This compares with 3.1 kph (1.9 mph) of a 2.2-ton whale shark, a speed not unexpected considering its huge body. Sunfish and salmon were the slowest. An 87-kilogram sunfish swam at 2.2 kph (1.4 mph) and a 3.3-kilogram salmon at 2.7 kph (1.7). The scientists used small monitoring systems attached to fish. The high speeds of the sharks and tuna are attributed to their unique body system that has evolved to keep their body temperatures relatively high. [Source:, January 16, 2017]

Shark tail shapes
According to “A 2.2-ton whale shark swam much faster than expected at 3.1 kph. The slowest of the species observed in the study were an 87-kilogram sunfish with a top speed of 2.2 kph, and a 3.3-kilogram salmon that swam up to 2.7 kph. The speed of fish with higher body temperatures is comparable to marine mammals who maintain a body temperature independently of their environment. The speed of the slower fish is much like that of reptiles, who cannot regulate their body temperature from within. “As a rule, the speeds of marine animals are decided by body temperature first, followed by body size,” Watanabe said.

“The shark is a cartilaginous fish while tuna have a bony skeleton. However, great white sharks and bluefin tuna have a common anatomy that makes them faster than other fish. Both have dark muscles where many blood vessels meet. Fish with lower body temperatures have very few blood vessels close to the surface of their bodies. These species of sharks and tuna also have a common structure called a rete mirabile. This a complex system of veins with cold blood and arteries with warm blood lying close together to prevent heat from escaping the body.

“As hunters of the outer seas where they are less concealed and more vulnerable to attack, speed is critical to the survival of great white sharks and bluefin tuna. The resemblance between these fish is a result of “convergence,” which is the evolution of unrelated animals to develop similar body characteristics in a common environment.

Shark Senses

Sharks communicate with vision, touch, sound, chemicals usually detected by smelling and electric signals) and employ pheromones (chemicals released into air or water that are detected by and responded to by other animals of the same species) and sense using vision, touch, sound. vibrations, electric signals and magnetism. [Source: Animal Diversity Web (ADW)]

According to Animal Diversity Web: All sharks have sense organs that help them communicate. These organs monitor both the outside and inside environments at all times. Some of these organs are spread around the entirety of the sharks' bodies and transmit nerve impulses. These nerve impulses are sent to two different areas in the sharks' bodies, their brain and their spinal cord. When there are signals sent to the brain, they comprehend them as just sensations. When signals are sent to the spinal cord, it results in a reflex reaction. [Source: Justin Alouf, Animal Diversity Web (ADW) /=]

Their lateral line— a narrow strip of sensory cells runs along the sides of the body and into the head. — detects vibrations in the surrounding waters. This aides in locating prey from great distances, as vibrations travel well in water. Sharks use their tastebuds, located in the roof, walls, and floor of their mouths to determine if food is palatable and to help them avoid noxious substances. Sharks also have organs that identify the location prey by measuring the amount of amino acids in the water and a lateral lines of vibration-sensitive hairs that run along their sides. Sharks hear and detect vibrations and they are most sensitive to low frequency vibrations, like those from injured fish and boats. They use the detection of these low frequencies to find food and to avoid humans.

Shark Vision, Smell and Hearing

Eye of a bigeyed sixgill shark
(Hexanchus nakamurai)

Shark and ray eyes lack cone cells which means they can not perceive color, except some blues and greens. For this reason most shark are grey or brown and lack elaborate design or markings. Sharks in general tend to have good eyesight especially in dim light. They can see underwater about three meters in front of them, depending on the depth and lighting. Their eyes glow when a flashlight is shown on them just like cat eyes do. Like cats, they have a special reflective layer behind their retina that helps them see in dim light. Because their eyes are on the sides of their heads, sharks have to move their heads from side to side to see objects in front of them. Sharks are very farsighted and they often develop cataracts.

Shark brains contain large olfactory bulbs that help provide them with a good sense of smell. They can use their sense of smell prey to locate prey as far as 1.7 kilometers away and detect concentrations of blood as low as one part per million, which is roughly equivalent to one drop of tuna blood in an Olympic size pool. Some species can detect a scent in a solution at concentrations of one part per billion. When ocean currents are flowing towards them they can detect blood over a half kilometer away. Sharks rely a great deal on smell to direct them towards food. Some sharks have a translucent "third eye" thought somehow to regulate their reproductive activity. Other have a clear membrane that covers their eyes to protect them.

Sharks have tiny holes on the top of their head that lead to very sensitive ears. There are three semicircular canals in the inner ear that help with balance. Sharks can hear the low frequency vibrations of distressed fish over long distances — at least one kilometer and perhaps kilometers away.. Another way sharks detect vibrations is by using their lateral line system. The lateral line system consists of pores that line the flanks of sharks that they can use for detecting vibrations of a distance about one to three meters.

Sharks and Electric Fields

Sharks have sensitive sensory organs called ampullae of Lorenzini in their noses and across the front of their head. These organs consist of minute, dark pores connected to jelly-filled canals that can detect electrical fields and movement as slight as the breathing of small fish or stingrays hidden in the sand. These organs are used by sharks in hunting and navigating according to earth’s magnetic fields.

Ampullae of Lorenzini are part of a shark's broader neuromast system. According to Animal Diversity Web: This systems organs consist of lateral lines, cephalic canals, and pit organs as well as ampullae of Lorenzini,. Neuromasts are all over the body as well as on the surface of the skin and in sunken canals that are beneath the skin. These organs help detect a wide variety of sensations and assist the sharks with the sensations of their surroundings. They can detect water movement and use it to orient their movement, detect sound waves, detects potential threats, and locate food. Some of the neuromast system uses electroreceptors that, when electric pulses are fired off, an electric field is transmitted all around the shark. When the electric pulses cease, the field fades away.[Source: Justin Alouf, Animal Diversity Web (ADW)]

Electroreceptors in a shark's head
Sharks have a higher sensitively to electric fields than any other animal. They can detect electrical fields 25 million times weaker than the faintest ones man can feel. Studies have shown that they orient themselves to the earth's magnetic fields. [Source: Eugenie Clark, National Geographic August 1981]

Shark prey is often hidden or buried and doesn’t move. Sharks pick up two kinds of electric fields that allow them to locate hidden, stationary prey: 1) AC fields generated by the contraction of muscles; and 2) DC fields that result from osmotic potential between the prey’s body tissue and seawater.

Dutch scientist Adrianus Kalmijn has conducted experiments that show how the ampullae of sharks pick up electric vibrations given off by struggling fish. In the experiments he buried a electrode that gave off an electric charge similar to one given off by a floundering flounder underneath the sand. Sharks responded when the electrode was turned on. Kalmijn also showed that sharks can detect an electric charge of five billionths of volt per centimeter, which is the equivalent of detecting a flashlight battery from 2,000 miles away. Kalmijn has shown that bacteria can navigate using the earth's magnetic fields.

Sharks Use Scent to Steer Toward Prey

Sindya N. Bhanoo wrote in the New York Times, “Sharks are scent hunters, using their noses to steer them toward unsuspecting prey. A new study finds that they do this by distinguishing which nostril the scent of food hit first, then swimming in that direction. The difference in timing between the scent hitting one nostril and the other can be as small as a tenth of a second, according to the study, published online last week by the journal Current Biology. [Source: Sindya N. Bhanoo, New York Times, June 14, 2010]

It had been thought that sharks compared the concentrations of smells entering each nostril and used this as a navigating tool. But timing is a better tool, because scents can travel through water in random, chaotic patterns, said Jayne Gardiner, the study’s lead author and a biologist at the University of South Florida. “If an animal is trying to use concentration, it might be very misleading,” she said. “Timing is a better cue, because it allows them to orient in the right direction.”

The researchers attached devices to the sharks’ heads with tubes feeding into the nostrils and pumped in the scent of squid, a food the sharks enjoy. They used smooth dogfish sharks, a species found near the Woods Hole Oceanographic Institution in Massachusetts, where Jelle Atema, the study’s second author, is based. The work was part of a larger project funded by the National Science Foundation to assess how sharks use all of their senses to locate, trap and capture food.

Sharks Likely Use Earth's Magnetic Field to Navigate

Ampullae of Lorenzini

Some shark species swim thousands of miles back to the same feeding grounds every year. Most likely they use Earth's magnetic field to orient themselves, a study published in 2021 demonstrates. Dogs, whales, sea turtles and other animals are also able to do this. Bryan Keller, a biologist at Florida State University who co-authored new study, likens this sense to "having an 'internal GPS.'" "This is, in my opinion, the best explanation for how migratory sharks successfully navigate during long-distance movements," Keller told Business Insider. [Source: Aylin Woodward, Business Insider, May 7, 2021]

Aylin Woodward writes in Business Insider: Nearly 2,000 miles below Earth's surface, swirling iron in the planet's outer core conducts electricity that generates a magnetic field. This field stretches all the way from the planet's interior to the space surrounding the Earth. It's what protects the world from deadly solar radiation.

“But the direction that the electromagnetic energy flows, as well as the strength of the resulting protective sheath, depends on where on the planet's surface you are. So animals that use the magnetic field to orient themselves do so by detecting these differences in field strength and flow. They then use that information to figure out where they are and where to go.

“Scientists long suspected sharks could navigate using the field, since the animals can sense electromagnetic fields in general. But that hypothesis had been difficult to confirm until Keller's study. His team examined the bonnethead shark, known as Sphyrna tiburo, because the species exhibits site fidelity — meaning it returns to the same estuary habitats each season. "This means the sharks have the capability to remember a specific location and to navigate back to it," he said.

The team captured 20 bonnetheads off the coast of Florida in the Gulf of Mexico, then placed the sharks in a 10-by-10-foot tank. They generated a tiny magnetic field within a 3-square-foot area of that tank. (Bonnetheads only reach 4 feet in length, which made them an ideal species to study in such a small pool, Keller said.)

“The team then tweaked that localized magnetic field to mimic the electromagnetic conditions of various locations hundreds of miles away from where they'd caught the sharks. If the animals were truly relying on magnetic-field cues to navigate, the thinking went, then the bonnetheads would try to reorient themselves and start swimming in the direction they thought would lead to the Florida coast. That's exactly what happened.

“When the researchers mimicked the conditions of the magnetic field on Florida's Gulf Coast, the animals exhibited no preference in which direction they were swimming — suggesting they assumed they were already in the right place."I'm not surprised that sharks garner map-like information from the magnetic field, because it makes perfect sense," Keller said.

Even though the new study was done on bonnetheads, Keller said the findings likely apply to other shark species as well. How else could a great white, for example, migrate from South Africa to Australia — a distance of more than 12,400 miles — then return to the exact same chunk of ocean nine months later? "En route to Australia, the animal exhibited an incredibly straight swimming trajectory," Keller said of great whites. "Given that the magnetic field is perhaps the only constant and ubiquitous cue available to these migratory sharks, it is sensible that magnetic-based navigation is responsible for facilitating these incredible navigational successes."

“Other navigational cues do exist, including currents and tides, but Keller said the magnetic field "is likely more useful than these other aids because it remains relatively constant." Biologists still aren't sure how sharks detect the field, but a 2017 study suggested that the animals' magnetic receptors are probably located in their noses.

Studying Sharks

Routine studies of sharks involve catching them on long lines, bringing them aboard a vessel, weighing and measuring them, determining their sex and recording whatever other information is gathered. In some cases sharks are injected with tetracycline, an antibiotic that leaves a mark on the shark’s back bone like a tree ring, so if the animal is ever dissected the scientists can determine how much time has passed. When all the data collecting is done a an identification tag is attached to the dorsal fin and a tiny piece of the fin is clipped for a DNA sample. Between 1991 and 2005 more than 13,000 sharks were tagged in the Gulf of Mexico from mid Florida to the Keys.

To determine what sharks eats you find out what’s in their stomachs. Describing the emptying of a shark’s stomach, Fren Shen wrote in the Washington Post, “The upside-down shark pinned under David McElroy’s arm wriggled madly but stopped when the researcher slid a 10-inch piece of plastic pipe way down its throat...Slowly McElroy withdrew the pipe. It spewed the slimy contents of the shark’s tummy — along with the tip of the glistening red stomach itself....Avoiding the two-foot-long creature’s teeth, McElory stuck in the stomach...”Aha!, he said leaning over the bucket of shark barf and pulling up a drippy chunk of fish skin the size of a potato chip. “It’s a kind of flatfish called a hogchoker....Very good.”

Biologists Samuel Gruber, who runs a shark research center in Bimini in the Bahamas, sets up nets in a sound near an area of mangrove swamps where young lemon sharks hang out. Describing the scene there Jennifer Holland wrote in National Geographic, “Self-described ‘shark geeks’ spend long nights working by moon and flashlight...carefully untangled captured lemon sharks and rushed them to a pen to be studied and later released. Nearly every pup that moves through the sound is caught this way. Each is weighed measured, tagged, and its dorsal fin clipped for DNA studies to help researchers build a lemon shark family tree. More than 90 percent of the tagged sharks that survive their first year are caught again in subsequent years, their health and growth recorded for comparison.” Gruber has been studying the lemon sharks for 25 years and has amassed the most detailed database of any shark population on Earth.”

Researchers from the University of Miami’s Rosenstiel School of Marine and Atmospheric Science and the University of New England have used the same ultrasound imaging technology used by medical professionals on pregnant women to study the reproductive biology of female tiger sharks. The study offers marine biologists a new technique to investigate the reproductive organs and determine the presence of embryos in sharks without having to sacrifice the animal first, which was commonly done in the past. [Source: David Goodhue, Miami Herald, April 17, 2016]

See Great White Sharks

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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