Tag Archives: sharks

Asian markets are driving sharks to extinction — but European fishermen are selling them fins

Countries from the European Union (EU) play a major role as suppliers and traders in the global shark trade, which is driving many species towards extinction, according to a new report. EU member states were the source of 45% of shark-fin-related products imported to Hong Kong, Singapore, and Taiwan in 2020, with Spain being the top exporter for fin trade.

Sharks are currently declining very fast on a global scale. One way humans hunt them is by using a practice called shark finning – the process of slicing off a fin and discarding the rest of the body, usually by throwing it back into the ocean, which leads to a slow and painful demise.

Fins are specifically targeted as they are used to make a fin soup in Asia, which is considered to be a symbol of status. Fishermen sometimes even prefer to practice shark fining instead of selling whole sharks in the market as fins are much more valuable and they get their money’s worth with relatively little work.

Finning is having big implications on shark populations worldwide. About 100 million sharks are killed globally every year, with many species such as the scalloped hammerhead susceptible to extinction.

Population plunges don’t only affect sharks but also entire ecosystems, causing a ripple effect. For example, the decline of the smooth hammerhead causes their prey, rays, to increase. If there are more rays, they eat more scallops and clams, which provide valuable services for the entire ecosystem. Simply put, if you remove the top predators from the ecosystem, the entire ecosystem’s biodiversity is affected.

The role of EU countries

In a new report, the International Fund for Animal Welfare (IFAW) analyzed almost two decades of customs data in three Asian trading hubs from 2003 to 2020. While the main market for fin-related products is in Asia, EU countries – especially Spain, the Netherlands, France, Italy, and Portugal – are big suppliers to this legal market.

“Small or large, coastal or high seas, shark species are disappearing, with the piecemeal management efforts to date failing to stop their decline,” report co-author and IFAW’s EU manager Barbara Slee said in a statement. “The EU, demonstrated by our report to be a key player in global shark markets, has an important responsibility.”

Over 188,000 tons of shark fin products were imported by Singapore, Taiwan, and Hong Kong from 2003 to 2020, with the EU responsible for almost a third. Spain was the top source of imports with over 51,000 tons shipped from 2003 to 2020, an annual average of 2,877 tons, according to the report. Portugal ranked second with 642 tons.

EU countries can’t carry out shark finning but the landing and sale of whole sharks are permitted, except for species protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). That’s why IFAW is now calling for all sharks to be listed under CITES, which would give them further protection.

Shark populations have been shown to recover when effective management is put in place, hence the importance of the CITES listing. If the EU would take a leadership role to ensure the accuracy of trade records and the enactment of sustainability requirements of sharks in trade, then other players would follow through, Barbara Slee added.

“Global shark declines are driven by international demand for shark fins and meat,” report co-author Stan Shea said in a statement. Although many place the burden of change on the consumptive countries, primarily in Asia, equally responsible for declines in shark populations are all countries with internationally operating fishing fleets.”

The full report can be accessed here.

LED-equipped fishing nets help protect wildlife from unintentional captures

Green light-emitting diode (LED) lights can help protect wildlife from fishing nets, new research reports.

Image credits Paul Lee.

Affixing green LED lights to fishing nets can significantly reduce the catch of nontargeted animals such as sharks, squids, or turtles, according to a team led by researchers from the Arizona State University. The addition of these lights doesn’t impact the quantity or quality of desired catch species (i.e. commercially-available fish), which helps raise confidence that fisheries will adopt the measure. That being said, the installation of these lights comes with a significant upfront cost per net, which many fisheries may not be able to afford.

Beyond practical concerns, however, the findings showcase that it is possible to maintain our current fishing efficiency while insulating species that aren’t desired from capture.

Lights in the deep

Coastal fisheries routinely use gillnets, devices that resemble chain-link fences, to capture fish. These nets are deployed for up to several days at a time and capture virtually every kind of marine wildlife that cannot fit through their holes. Undesired captures (“bycatch”) are tossed overboard once the nets are recovered. These animals experience very high rates of death following this, adding up to significant pressure on marine species such as dolphins and sea turtles. It also impacts the fisheries’ bottom line, as personnel waste time removing these animals from the nets.

In other words, both business and nature lose out from the use of gillnets.

John Wang, a marine ecologist at the National Oceanic and Atmospheric Administration (NOAA), and his colleagues previously designed illuminated nets in order to protect turtles from becoming bycatch, back in 2016. Turtles seem to be particularly good at noticing green light, and these nets cut down on turtle bycatch by 64%. The current study builds on those findings, examining whether other marine animals could benefit from the same idea.

It turns out, they would. The authors worked with small-scale grouper and halibut fisheries in Baja California, Mexico, as the area is known for its large populations of turtles and other large marine species. They deployed 28 pairs of nets, one of each being equipped with groups of green LED lights every 10 meters. The team gauged their efficiency by identifying and weighing the animals each net captured overnight.

Nets outfitted with lights captured 63% less bycatch overall. Per species, they reduced bycatch by 51% for turtles, 81% for squid, and 95% for elasmobranchs (sharks and rays) — the last one being the most “gratifying” result for the authors, as shark bycatch in the Gulf of California is “a huge issue”.

Fish capture was not affected by the lights. However, the LEDs cut down on time wasted by fishermen on hauling and unloading bycatch, and on untangling the nets, by half. The only drawback so far, according to Senko, is the upfront installation costs of the lights: around $140 per net. Some fisheries, especially those in poorer areas such as Indonesia and the Caribbean, simply can’t afford this price per net, they add. The team is toying with using fewer lights and having them be solar-powered rather than battery-powered to reduce some of these costs. Meeting the needs of fisheries is essential for the success of this project, as they are the ones who will decide on using the LED nets or not.

Exactly why some animals seem to avoid lights, and why they do so more than others, is still up for debate. While it is possible that some species’ better eyesight helps them perceive the lights more clearly, it’s very unlikely that this is the cause — any species with sight can see these lights, after all.

The paper “Net illumination reduces fisheries bycatch, maintains catch value, and increases operational efficiency” has been published in the journal Current Biology.

Fish like to rub on sharks, strangely enough, and use them as exfoliating soaps

In a somewhat surprising twist, new research finds that fish actually seek out sharks and… rub against them.

Shark. Original public domain image from Wikimedia Commons

What’s the most dangerous animal you’ve ever patted? For most of us, it’s probably a particularly feisty dog. Fish throughout the seven seas, however, put us to shame, it would seem. According to a collaborative research effort led by the University of Miami (UM) Shark Research and Conservation Program at the Rosenstiel School of Marine and Atmospheric Science, fish seek out sharks and chafe against them.

Such behavior is frequent and widespread, the team explains, which suggests that shark chafing could play an important ecological role for sea dwellers.

Dancing with the devil

“While chafing has been well documented between fish and inanimate objects, such as sand or rocky substrate, this shark-chafing phenomenon appears to be the only scenario in nature where prey actively seek out and rub up against a predator,” said UM Rosenstiel School graduate student Lacey Williams, who co-led the study with fellow graduate student Alexandra Anstett.

It’s not the first time we’ve seen fish engage in such behavior, but the study is our first reliable source of data on just how widespread and pervasive this behavior actually is.

The team pooled together underwater photos, videos, and drone footage for the research. In this body of data, they found 47 instances of fish engaging in chafing behavior with sharks. These chafing events took place in 13 different locations around the world and lasted anywhere from eight seconds to five minutes. Multiple species were involved, both in regards to fish and to the sharks being chafed-upon. Twelve different species of finfish were seen chafing against eight species of shark, including the infamous great white sharks. At least one interaction involved silky sharks (Carcharhinus falciformis) chafing on the head of another shark — a whale shark, in this particular case. The single largest group of fish that the team recorded during a single chafing event numbered in excess of 100 individuals.

Another dataset — aerial drone surveys of Plettenberg Bay, South Africa — revealed a further 25 cases of shark-chafing, involving leerfish (garrick, Lichia amia) and a passing white shark.

All of this is fine and well, but obviously leaves a big question unanswered: why would fish intentionally seek out and rub against their predators?

“While we don’t exactly know why it’s happening, we have a few theories. Shark skin is covered in small tooth-like scales called dermal denticles, which provide a rough sandpaper surface for the chafing fish,” said UM Rosenstiel School research associate professor and study co-author Neil Hammerschlag. “We suspect that chafing against shark skin might play a vital role in the removal of parasites or other skin irritants, thus improving fish health and fitness.”

In other words, fish might use sharks for the same purpose we use fancy soaps: exfoliation. Rubbing against sharks likely helps fish remove bacteria and parasites from their skins. Sharkskin is covered in tooth-like scales known as denticles, V-shaped structures that reduce turbulence and drag, allowing them to swim faster and with less effort. Presumably, these same denticles make them very good exfoliators, as well.

The paper “Sharks as exfoliators: widespread chafing between marine organisms suggests an unexplored ecological role” has been published in the journal Ecology.

Sharks have spiral-like intestines that resemble one of Nikola Tesla’s inventions

A CT scan image of the spiral intestine of a Pacific spiny dogfish shark (Squalus suckleyi). The structure is similar to the design of the Tesla one-way valve. Credit: Samantha Leigh/California State University Dominguez Hills.

Despite years of research, the exact structure and mechanics of shark intestines have been poorly understood until now. In a new study, researchers employed modern imaging tools to peer through the guts of various sharks, revealing that the spiral-shaped intestines remarkably function in a similar way to a Nikola Tesla patent for an unusual valve with no moving parts.

Marine biologists have had to rely on 2D sketches in order to study sharks’ digestive systems. Understanding how sharks’ intestines function has far-reaching consequences because these top-of-the-food-chain apex predators impact other species through what they eat and excrete.

Researchers at California State University Dominguez Hills, the University of Washington, and the University of California, Irvine embarked on a new study to fill in gaps in our knowledge that have eluded scientists for more than a century.

The reason why shark intestines are difficult to study has to do with their complex structure, with many overlapping layers. Dissecting a shark can destroy the context and connectivity of the tissue, which would be like “trying to understand what was reported in a newspaper by taking scissors to a rolled-up copy. The story just won’t hang together,” said Adam Summers, a professor at the University of Washington’s Friday Harbor Labs and co-author of the new study.

But this is where modern tools come in. The researchers used computerized tomography (CT) scanner to create 3D scans of intestines from nearly three dozen shark species. This machine takes X-ray images from different angles, then a computer algorithm stitches these different images together to create a 3-D image without harming or disturbing the tissues in any way or form. Before scanning them, the researchers made sure to fill the intestines and freeze-dried them in order to preserve their natural shape.

“It’s high time that some modern technology was used to look at these really amazing spiral intestines of sharks,” said lead author Samantha Leigh, assistant professor at California State University Dominguez Hills. “We developed a new method to digitally scan these tissues and now can look at the soft tissues in such great detail without having to slice into them.”

These scans serve to explain the odd shape of the shark’s intestines. Unlike most animals that have tubular intestines, sharks have spiral-shaped intestines that slow down the food as it moves downward through the gut due to gravity and peristalsis (the contraction of the gut’s smooth muscles). This shape allows food to move in only one way aided by gravity with virtually no energy expenditure.

That’s a very similar design to the “valvular conduit”, also known as a “Tesla valve”, patented by Nikola Tesla in 1920. Tesla’s invention is a one-way fluid valve with no moving parts consisting of a pipe with an intricate series of diverting teardrop-shaped loops.

Not all shark intestines are the same, though. There are four different kinds of spiral intestines, the researchers found. These organs can be columnar (like a spiral staircase), scroll (like a rolled-up sheet of paper), and either upward-facing or downward-facing funnels.

A CT scan image of a dogfish shark spiral intestine, shown from the top looking down. Credit: Samantha Leigh/California State University Dominguez Hills.

Sharks have wacky intestines for a reason. The researchers believe the spiral-shaped intestines allow sharks to hold food in their system for a longer time and absorb more nutrients than animals with tube-shaped digestive systems. Sharks are known to go days or even weeks without food if they have to, and their Tesla-valve-like intestines may play an important role.

The researchers also performed experiments to see with their own eyes how this spiral structure works. Intestines from five recently euthanized Pacific spiny dogfish sharks (Squalus suckleyi) were filled with colored liquids with different thicknesses. This allowed them to observe that the intestines “mix and churn” the liquids rather than pushing them along.

Beyond learning more about how sharks function, these findings have important implications for marine ecology. As top predators of the open ocean, sharks eat anything from fish and mammals to seagrass.

“The vast majority of shark species, and the majority of their physiology, are completely unknown. Every single natural history observation, internal visualization and anatomical investigation shows us things we could not have guessed at,” Summers said. “We need to look harder at sharks and, in particular, we need to look harder at parts other than the jaws, and the species that don’t interact with people.”

The researchers claim that this research could also inspire new technology that mimics shark intestine function, which may prove useful in certain industries where matter needs to flow in one direction with only minimal energy use. Potential applications include filtering microplastics from the water and industrial fluid-pump technologies.

The findings appeared in the journal Proceedings of the Royal Society B.

No GPS needed: Sharks use Earth’s magnetic field to navigate the seas

Every year, thousands of great white sharks’ (Carcharodon carcharias) travel from South Africa to Australia, following an almost perfect straight line across the ocean. They don’t have any signs to guide them and no stable landmarks by which they can set their course — yet they carry on in the same way, year after year. Researchers now know how they do it.

Image credit: Wikipedia Commons

Many have speculated that sharks could be using the Earth’s magnetic field as an atlas, just as several other animals do. But this was hard to prove as sharks are notoriously difficult to study. It’s tricky to keep them in captivity and to design an experiment big enough to test them in a laboratory — but in a new study, researchers were able to pull it off. 

A team from Florida State University found that sharks have an internal navigation system which allows them to use Earth’s magnetic forces to travel long distances with accuracy. They subjected 20 bonnethead sharks (Sphyrna tiburo) to “magnetic displacement” exercises that replicated geographical locations from where they were captured.

“We’ve known for some time they have the ability to detect the magnetic field, this is the first time that’s tested successfully that they use those abilities to infer their location or if they’re garnering map-like information from the magnetic field,” Bryan Keller, lead author, told The Guardian. “We expect these abilities are also observed in other species.”

For the study, the researchers built a wooden cube with a large tank at the center and then coiled copper wiring around the cube at precise intervals.

When connected to power, the copper conducted electrical current and created a magnetic field. The team could create a stronger or weaker field by adjusting the power to mimic the conditions the sharks encounter in the oceans. 

They tested the sharks in three artificially generated magnetic fields. One was like the field they’d naturally encounter in Florida, where they were captured. Another one was like the field at a point 600 kilometers south along their migratory route, and another was like a point 600 kilometers north in Tennessee, where the sharks had never been to.

The animals didn’t produce a response to the field from their home area or to the one mimicking the northern location. But when they were exposed to the magnetic field like the one they would find south in their migratory route, they consistently oriented themselves with their heads pointing to the north. This means sharks use this information to decide which direction to travel. 

“The question has always been, even if sharks are sensitive to magnetic orientation, do they use this sense to navigate in the oceans, and how?” Robert Hueter, a retired senior scientist at Mote marine laboratory on Florida’s west coast, told the Associated Press. “These authors have made some progress at chipping away at this question.”

While very useful, the finding doesn’t explain how sharks’ sense magnetic fields. Still, there are a few theories. One argues that animals have magnetite crystals, which sense true north, embedded somewhere in their brains or nervous systems, while another one believes that magnetic fields affect receptors in their visual systems.

Sharks also have pores in their snouts filled with receptors which detect electrical currents in the water, known as the “ampullae of Lorenzini”. They find prey by electrically sensing their heartbeats and researchers suspect these receptors double as magnetic fields, or pick up on them indirectly by noticing how they interact with electrical currents.

But nothing is certain yet. 

The study was published in the journal Current Biology. 

What are the different types of shark species

Did you know sharks are older than trees? Sharks first appeared almost 400 million years ago and have been extraordinarily resilient, having survived all five global mass extinctions, including the Permian-Triassic extinction that wiped out 95% of all life on Earth.

Today, more than 450 species of shark swim throughout the world’s salt and fresh waters. Here’s a list of some of the most common or memorable types of shark.

Whale Shark (Rhincodon typus)

Whale shark at Georgia Aquarium. Credit: Wikimedia Commons.

Sharks are cartilaginous fish and the huge whale shark is not only the biggest shark but also the largest fish in the world. The slow-moving whale shark can measure up to 12.6 meters (41.5 feet) in length and weigh 20 tons. That’s about the size of a school bus.

That may sound frightening, but the good news is whale sharks aren’t predators. The elusive shark is a filter-feeding shark, whose diet consists of krill, fish eggs, crab larvae, and only occasionally any small fish or octopus that gets caught in its 1.5-meter (4.9-foot) wide mouth. According to researchers at the  Atmosphere and Ocean Research Institute, whale sharks can survive for weeks without food. During such starvation periods, they may ingest seaweed and other plants.

The species is classified as endangered by the International Union for the Conservation of Nature. Their numbers and habitat have decreased dramatically over the last decades, primarily due to human activity like offshore drilling and fishing.

Angelshark (Squatina)

Japanese angelshark (Squatina japonica). Credit: Wikimedia Commons.

Angelsharks were once one of the most abundant shark species swimming in the coastal waters of Western Europe and Northern Africa. They have flattened bodies and wide pectoral fins, which make them look similar to rays.

Although they can be found all over the world, nowadays angelsharks remain most abundant in the western and eastern sides of the Atlantic and Pacific oceans, respectively, where they linger on the very bottom of the ocean. These sharks stay buried in the sand and mud of the ocean floor, with only their eyes poking out. They can stay in this position for days at a time, waiting for their favorite prey — typically fish, crustaceans, or mollusks.

Humans have long known about them, with angelsharks mentioned in ancient writings by such authors as Aristotle, Mnesitheus, Diphilus, and Pliny the Elder, who considered the angelshark’s meat as an important food source and its skin as a useful material for polishing ivory and wood.

Unfortunately, overfishing has driven the angelshark close to extinction, with populations estimated to have declined by up to 90% in the past 45 years. The IUCN lists the angelshark as critically endangered.

But there are also reasons to be optimistic. Angelshark fishing has been illegal in the Mediterranean Sea since 2011 and in all coastal waters of any EU member country since 2010.

Shortfin Mako Shark (Isurus oxyrinchus)

Shortfin mako shark in the north atlantic at Condor Bank, Azores. Credit: Wikimedia Commons.

The Shortfin Mako is thought to be the fastest of all sharks, having been recorded swimming up to 32 km/h (20 mph).

These sharks have very pointed snouts and long gill slits. They grow slowly but can reach up to 13 feet long (4 meters) and live to be over 30 years old.

Shortfin makos are very aggressive predators that feed near the top of the food chain on large marine fishes such as swordfish, tuna, marine mammals, and even other sharks. They’ve also been blamed for some reported shark attacks on humans, though most involved fishermen who dragged hooked makos into their boats.

Prior to their attack, makos swim in figure-eight patterns and approach their prey with their mouths open.

Makos are highly migratory and can travel across entire oceans, although they prefer waters off the coast of New England and the Mid-Atlantic. Due to overfishing, stocks of mako sharks have been dramatically depleted, compelling the World Conservation Union to list them as “Near Threatened”.

Hammerhead Shark (Sphyrnidae)

Scalloped Hammerhead Shark  (Sphyrna Lewini). Credit: Wikimedia Commons.

The hammerhead sharks are a group of sharks that form the family Sphyrnidae. They’re also among the most recognizable sharks in the world due to the distinctive hammer-shaped structures of their heads.

Although they might look dweeby, hammerheads are actually fierce predators that live in warm tropical waters and feast on a wide variety of marine creatures. The hammerheads use their wide heads to trap stingrays by pinning them to the seafloor. The peculiar eye placement, on each end of its very wide head, allows the hammerhead shark to scan a larger area more quickly than other sharks are able to.

Unlike most other fish, female hammerheads don’t lay eggs. Instead, they give birth to live young, up to 50 pups at a time. When they’re babies, though, the hammerheads have more rounded heads than their parents.

They’re not aggressive towards humans, although a few attacks have been reported throughout history.

Zebra Shark (Stegostoma fasciatum)

Zebra-shark (Stegostoma fasciatum). Credit: Wikimedia Commons.

The zebra shark is a species of carpet shark and the sole member of the family Stegostomatidae. They are very large sharks that live in the shallow coral reef habitats in tropical waters of the Western Pacific and Indian Oceans.

The sharks owe their name to yellowish stripes that cover their brown bodies when they’re young. When they reach adulthood, the zebras shed their stripes for small back dots, resembling leopard sharks.

Zebras are nocturnal foragers and solitary creatures that hunt small fish, snails, sea urchins, and crabs. Although they’re sizable, growing up to 2.5 meters (8 feet) in length, zebras are totally harmless to humans. In fact, they adapt well to captivity, making them a common attraction at many aquariums around the world.

Unfortunately for the zebras, many find their fins delicious, which are sold fresh or salt-dried in markets throughout Indonesia, Thailand, Malaysia, Philippines, and elsewhere. Due to overfishing, zebras are considered endangered by the IUCN Red List

Basking Shark (Cetorhinus maximus)

Basking Shark – Cetorhinus maximus. Credit: Pikrepo.

One of the most awe-inspiring fish and the second-largest shark species, basking sharks are easily recognizable by their long gill slits which almost encircle the head and their pointed snout.

Some grow as large as 12 meters (40 feet), and due to their intimidating, almost predatory appearance many are frightened by them. However, basking sharks are quite harmless, spending most of their time with their oversized mouths open, filtering out their favorite prey — plankton. An adult basking shark swimming at a constant speed of two knots passes about 2,000 gallons of water over its gills per hour! An individual shark may have as much as a half-ton of food in its stomach.

Basking sharks are one of the few species that live in temperate latitudes, both north and south of the equator. They’re also very social animals, most often being spotted in groups of 2 or 3 individuals, and sometimes up to very large groups of 500 or more.

Bull Shark (Carcharhinus leucas)

Bull shark in Bahamas waters. Credit: Wikimedia Commons.

Most people are most frightened by great whites, but if there’s one shark you should stay clear of, that’s the bull shark. This is a highly aggressive species of shark, which tends to hunt prey in tropical water around coasts frequented by humans.

Bull sharks get their name from their short, blunt snout, as well as their highly quarrelful tendencies. Often, these sharks will head-butt their prey before approaching for an attack.

These are common sharks found in warm, shallow waters across the world’s oceans. Fast and agile, these predators will eat almost anything they pick up on their radar, including fish, dolphins, and other sharks. No humans, though, although there have been reported attacks — mostly inadvertent attacks or out of curiosity.

Nurse Shark (Ginglymostoma cirratum)

Nurse shark swimming. Credit: Wikimedia Commons.

These are perhaps the most sluggish and sedentary of all sharks. These couch potatoes of the shark world rest by day, preferring to slowly creep over the sandy ocean floors during the night, slurping up little animals in the shallow, coastal waters.

As a fun fact, these slow-moving carnivores sometimes use their pectoral fins to “walk” across the bottom of the oceans. They also have fleshy sense organs on their faces, known as barbels, which they drag across the sand in search of prey — fish, shrimp, and squid.

Nurse sharks are abundant throughout their range in the warm, shallow waters of the western Atlantic and eastern Pacific oceans.

Tiger Shark (Galeocerdo cuvier)

Credit: Wikimedia Commons.

True to its name, the tiger shark is one of the sea’s fiercest and mightiest creatures. However, the name itself more so refers to the dark stripes on their sides and backs.

These slow-moving sharks live all across the world in subtropical water, where they subsist on an omnivorous diet.

Tiger sharks are famous for their incredible senses of sight and smell, being able to react to even the faintest traces of blood, which makes them excellent scavengers. They’re so sensitive, it’s said they can even detect electricity.

Aside from reaching 4 meters in length (14 feet) and weight up to 635 kg (1,400 pounds), the tiger sharks can be intimidating due to their sharp and highly serrated teeth. Their jaws are so powerful they can easily crack open the shells of sea turtles and clams, although they’re known for also eating stingrays, seals, birds, squids, as well as the occasional old tires and license plates. Unfortunately, humans are also sometimes on the menu. Alongside great whites, tiger sharks have earned a reputation for attacking people.

Due to fishing for their fins, skin, flesh, and livers, tiger sharks are listed as near threatened.

Blue Shark (Prionace glauca)

Blue Shark – Prionace glauca. Credit: Pikrepo.

With their big eyes and small mouths, blue sharks are perhaps the cutest of them all. They get their name due to their dark blue backs and lighter blue sides. Curiously, their indigo color quickly changes to a uniform dark grey if they are pulled out of the water.

The curious, open-ocean predators are also recognizable for their exceptionally slender body and elongated conical snout. Often, they are seen swimmingly slowly at the surface with the tips of their dorsal and caudal fins out of the water.

Their favorite food is squid and herring, although they’re known to occasionally munch on the carcasses of whales and turtles. No longer than 3 meters (10 feet), blue sharks are not aggressive with humans although they’re known to approach divers, being highly curious fish.

The blue shark is estimated to be the most heavily fished shark in the world, with annual global catch estimates of around 20 million individuals each year. Oddly enough, they’re not targeted for their meat or fins. Instead, they’re simply bycatch of longline and driftnet fisheries. For this reason, they are classed as ‘Near Threatened’ on the IUCN Red List.

Thresher Shark (Alopiidae)

Thresher Shark. Credit: Wikimedia Commons.

Thresher sharks are large sharks of the family Alopiidae that are found in all temperate and tropical oceans, and whose defining feature is their weaponized tails.

In the case of most sharks, it’s their front ends you should be worried about. But with threshers, you need to be careful at both ends. When attacking prey, the thresher slings the scythe-shaped tail tip over its head like a trebuchet with an astonishing top speed of 128 km/hour (80 mph). The impact can be devastating, stunning fish or outright killing them on the spot. The shark then simply swims round and has its pick.

This extraordinary predatory behavior, however, is very rare to spot. Threshers hunt in the open ocean and usually during the dark.

Silky Shark (Carcharhinus Falciformis)

Silky shark (Carcharhinus falciformis) at Jardines de la Reina, Cuba. Credit: Wikimedia Commons.

Named after its smooth skin (a result of densely packed dermal denticles), the silky shark is a highly migratory species of shark found in subtropical waters in the western Atlantic, Pacific, and Indian Oceans.

Like the thresher, the silky shark’s pectoral fin is shaped like a sickle. Another distinctive feature of silky sharks is the shape of their teeth. On each side of their upper jaws, they have 14 to 17 teeth that are notched or serrated rather than concave.

Pacific Sleeper Shark (Somniosus pacificus)

Sleeper Shark. Credit: Wikimedia Commons.

Pacific sleeper sharks are large deep-water sharks that reach about 4.4 meters (14 feet) in length. Thought to be relatively common, sleepers are lumbering and sluggish creatures that can be found in the North Pacific from Japan to Mexico. Their sluggish nature is also why they’ve been named sleeper sharks.  They probably rarely exceed speeds of a few miles per hour (5 km/hr).

Leopard Shark (Triakis semifasciata)

A leopard shark (Triakis semifasciata) and two blacksmith damselfish (Chromis punctipinnis), swimming in a kelp forest in the 70,000 gallon (approx. 265,000 litre) kelp tank at Scripps Aquarium in La Jolla, California, United States. Credit: Wikimedia Commons.

Leopards are among the most common sharks off the coast of California. They’re named after their leopard-like dark spots over their silver or grey bodies.

Leopard sharks love to swim near the ocean floor, where they spend most of their time just a foot or so above the bottom. This is because they, like all sharks, lack the swim bladders that other fish use to fine-tune their buoyancy. Instead, a leopard shark stores oil in its enormous liver to balance its weight.

There have been no fatal attacks on humans by leopard sharks, although leopard sharks are occasionally caught in fishing nets and consumed for food. However, because of the high mercury content of its flesh, scientists warn against consuming this shark.

Lemon Shark (Negaprion brevirostris)

Lemon Shark (Negaprion brevirostris). Credit: Wikimedia Commons.

Lemon sharks are easy to spot due to their yellow to brown dorsal color, which helps them camouflage against the sandy seabed. These medium-sized nocturnal predators usually hunt fish cooperatively in small groups — especially when drops of blood unleash a feeding frenzy.

Although the lemon shark is an aggressive predator, they are thought to be harmless to people. If anything, the lemon shark should be worried about humans, who are responsible for the rapid destruction of mangrove coastlines that protect baby lemon sharks from larger predators. For this reason, the lemon shark is classified as ‘Near Threatened.’

Oceanic Whitetip Shark (Carcharhinus longimanus)

The Whitetip reef shark (Triaenodon obesus) is shy and flees from divers. Credit: Wikimedia Commons.

Oceanic whitetips are famous for attacking shipwrecked sailors in tropical and subtropical waters. Some of their defining features include white-tipped first dorsal, pectoral, pelvic, and tail fins. Sadly, humans took their revenge a bit to the extreme.

“We’ve absolutely annihilated the species on a global scale,” says Demian Chapman, one of the few scientists who have studied the shark. “And yet when I say ‘oceanic whitetips,’ a lot of people have no idea what I’m talking about.”

The once abundant, now elusive whitetip shark is listed as ‘Threatened’ under the Endangered Species Act.

Blacktip Reef Shark (Carcharhinus melanopterus)

Blacktip reef shark (Carcharhinus melanopterus). Credit: Wikimedia Commons.

The blacktip reef shark is commonly seen in many tropical reefs, where it swims through the shallow waters. It’s a small-medium-sized shark that is easily recognizable thanks to its black fin tips with white highlights.

Since they’re totally harmless to humans and they like to live in reefs, blacktip reef sharks are a popular species in dive tourism. They’re also frequently displayed in aquariums.

White Shark (Carcharodon carcharias)

Great white shark (Carcharodon carcharias) off South Africa. Credit: Wikimedia Commons.

The undisputed king of the ocean needs no formal introduction. With a maximum size estimated at 6 meters (20 feet) and weighing more than 1,800 kg (4,000 pounds), the white shark is the largest predatory fish on Earth.

The white is found in cool, coastal waters around the world, where it preys on other sharks, crustaceans, molluscs, and sea birds. Its mouth is lined with up to 300 serrated, triangular teeth arranged in several rows.

But despite its reputation as a man-killer, which was largely amplified by the cult classic movie Jaws, great white attacks are very rare. In fact, every year there aren’t more than 80 reported shark attacks in the entire year — that includes great whites, tiger sharks, bull sharks, and every other species of shark. That’s all, just 80. Most attacks are hit-and-run in which the shark bites and then leaves, and are usually non-fatal.

There’s no reliable data on its population size, but scientists agree that great white shark numbers are dwindling precipitously. The species is currently classed as ‘Vulnerable ‘ — which is one step away from ‘Endangered’ — by the IUCN.

Megalodon’s giant size was truly unprecedented among all sharks ever

Schematic drawing showing the distribution of maximum possible sizes of all known 70 non-planktivorous genera (groups) in the shark order Lamniformes, comprising modern (in gray) and extinct (in black; with hypothetical silhouettes) members and in comparison with an average adult human (in red) as scale. Megalodon clearly stands out. Credit:  Kenshu Shimada, DePaul University.

Sharks are among the most amazing creatures there are. Not only are they older than mammals and dinosaurs, their 450-million-year-old evolutionary history means that they even preceded trees! Perhaps the fiercest shark that ever swam the world’s oceans was Otodus megalodon, an extinct species of shark that lived from the early Miocene to the end of the Pliocene, between 23 to 2.6 million years ago.

If there’s one defining feature that Megalodon is remembered for, that would be its size. Huge is really an understatement. Although its exact size is still a matter of contention among paleontologists and shark experts, the fossil record suggests that Megalodon could exceed 15 meters (50 feet) in length. And, according to a new study published today in the journal Historical Biology, no other shark came close to it.

Megalodon: the uncontested king of the sharks

Famed fossil hunter Vito Bertucci with a megalodon jaw, measuring 3,4 m. (11 ft.) across and almost 2,8 m. (9 ft.) in height. It took her almost 20 years to reconstruct the jaw.

Like all sharks, Megalodon’s skeleton was mostly made of cartilage. This means that only its teeth and vertebrae have survived in the fossil record. But these are enough to infer many qualities about this fascinating ancient marine beast.

For more than two decades Kenshu Shimada, a professor of paleobiology at DePaul University in Chicago and research associate at the Sternberg Museum in Kansas, has been studying Megalodon teeth and gathering data from the scientific literature. Shimada’s aim was to plot Megalodon’s size and compare it to other sharks. What he found was truly shocking.

“The initial goal of this new study was to investigate the size distribution of sharks in the order Lamniformes over geologic time by developing a logical method to estimate the body, jaw, and dentition lengths from their teeth. We did expect Megalodon to be gigantic based on my previous study,  but what surprised us was actually seeing in our data a 7-meter-gap [23-foot-gap] between the size of Megalodon and the size of the next largest non-planktiviorous (i.e. carnivorous sharks that don’t eat plankton) lamniforms not directly related to Megalodon in the entire geologic history,” Shimada told ZME Science in an email.

“The significance of this new study is that it represents the first collective analysis surveying the body sizes of all major lamniform shark lineages including both extinct and living forms. It demonstrates Megalodon was uniquely gigantic relative to other non-planktivorous sharks,” he added.

A comparison between a megalodon (black) fossilized tooth and two great white shark teeth.
Image via Wikimedia.

Shimada estimated the size of various species of extinct lamniforms from the fossil record based on measurements taken from present-day, living non-planktivorous lamniforms. Also known as mackerel sharks, lamniforms include some of the most familiar species of sharks, such as the great whites.

After the tally was made, the researchers were amazed to find that the next runner up behind Megalodon was very far behind. While Megalodon’s size could exceed 14.1 meters (46 feet), all other sharks, including extinct species, generally capped at 7 meters in length (23 feet).

Some plankton-eating sharks came close to Megalodon, such as whale sharks and basking sharks, however, carnivorous sharks were far behind. The exact reasons why are yet unclear.

“There are still so many fundamental questions about Megalodon scientists are still trying to answer. While Megalodon bite marks on marine mammal bones are known, whether they represent predatory attacks or scavenging activities are still unknown. Related to our new study, exactly how large Megalodon could have reached remains uncertain where, at present, the scientifically justifiable maximum length estimates are in the range of 14.1-15.3 meters (46-50 feet). The validity of a recent study on the body form of Megalodon also needs to be tested or substantiated. This does mean that individuals larger than 15.3 meters did not exist, but simply the existence of such over-sized individuals has not been substantiated in the realm of science yet. Among many other questions, exactly why Megalodon became extinct also remains to be a big unanswered question,” Shimada said.

According to the study, lamniformes were well represented in the late Mesozoic-Cenozoic fossil record, a time during which they showed remarkable diversity and specialization. And since most of them were carnivores, the researchers assert that these ancient lamniforms must have played a major role in the evolution of marine ecosystems throughout geological time.

“The fossil record is a window into the evolution of ecosystems, and understanding why species become extinct, and how their rise and demise affected their ecosystem is critical to today’s oceans for issues like conservation of organisms, habitat preservation, and sustainable marine natural resources. Elucidating ecological variables as simple as the body size of organisms, especially carnivores like sharks in our new study, is the first step. While much of the attention has been given to the question, “Why Megalodon evolved to be so large?”, our new study has provided another way of thinking about the issue for future scientific studies, that is to ask ‘Why all other non-planktivorous lamniforms have had a general size limit of 7 meters [23 feet]?'” Shimada concluded.

With empty beaches, sharks are returning to Israel’s coast

Israel’s beaches are pretty empty these days, but some are enjoying them more this way. Dozens of spotted sandbar sharks have been spotted on Israel shores by researchers at the University of Haifa.

The sharks were spotted off the coast of Ashdod, Israel’s sixth-largest city and the largest port in the country. Researchers at the University’s Morris Kahn Marine Research Station witnessed a large group of sharks swimming off Ashdod’s coast, presumably emboldened by the decrease in human activity.

It was impressive to see the sharks in such large numbers, particularly as the overall population numbers seem to be decreasing, which recently led their designation as a “vulnerable”.

Furthermore, this comes just days after another spotting off the Israelian city of Hadera. In Hadera, the sharks were moving towards the warmer water near Hadera’s power plant.

“This current sighting of sandbar sharks has occurred in several places around the world, but it is rare to see them in the Mediterranean,” said marine biologist Aviad Sheinin, also the top predator project manager at University of Haifa. “It seems that while most of the Mediterranean sharks are in danger of extinction, our beaches are exceptionally friendly to them.”

It’s not the first time sharks off the coast of Israel have drawn scientific interest. University researchers and students have been monitoring the sharks off the coast of Hadera for five years, tagging them with GPS trackers and monitoring their patterns.

A researcher in a kayak studies sharks in the shallow waters near Hadera, Israel. Photo by Hagai Nativ/Morris Kahn Marine Research Station/University of Haifa.

Unfortunately, due to the coronavirus pandemic, the university’s research has also been put on hold for the past two months. This prevented researchers to truly take advantage of this opportunity and tag the sharks properly, which would have allowed them to trace the movement of the sharks. For now, they are only following the sharks remotely, keeping an eye on any sightings.

Understanding the dynamics of this population is particularly important as their numbers seem to be steadily decreasing. Throughout the Mediterranean, these sightings are very rare and are almost exclusively restricted to the Israelian coast. It’s not clear why the sharks prefer Israel.

“The number of sharks in the Mediterranean Sea is decreasing due to over-fishing of their food, or the fishing of the sharks themselves unintentionally,” Dr. Sheinin concluded. “Part of the research is focused on trying to reduce their unintentional grouping, in a bid to help preserve them.”

Unique molecules allow sharks to glow in the dark

Transforming the ocean’s blue light into a bright green color is a known ability by certain shark species. But the change of color, only seen by them, couldn’t be clearly explained by science yet. New research has brought new insight into the reasons for the phenomenon.

Credit: Flickr

A group of researchers has identified that the shark’s bright green hue is caused by a previously unknown family of small-molecule metabolites. The mechanism is different from how most marine creatures glow and could also have useful roles for sharks, including helping them identify each other in the ocean and fight against microbial infections.

“Studying biofluorescence in the ocean is like a constantly evolving mystery novel, with new clues being provided as we move the research forward,” said David Gruber, co-corresponding author of the study. “After we first reported that swell sharks were biofluorescent, my collaborators and I decided to dive deeper into this topic. We wanted to learn more about what their biofluorescence might mean to them.”

Working with Jason Crawford, a professor at Yale University, Gruber focused on two species of sharks, the swell and the chain. They noticed that their skin had two tones, light and dark, and extracted chemicals from the two skin types. They found a type of fluorescent molecule that was only present in the light skin.

“The exciting part of this study is the description of an entirely new form of marine biofluorescence from sharks–one that is based on brominated tryptophan-kynurenine small-molecule metabolites,” Gruber said.

 These types of small-molecule metabolites are known to be fluorescent and activate pathways similar to those that, in other vertebrates, play a role in the central nervous system and immune system. But in the sharks, the molecule variants account for the biophysical and spectral properties of their lighter skin.

“It’s a completely different system for them to see each other that other animals cannot necessarily tap into. They have a completely different view of the world that they’re in because of these biofluorescent properties that their skin exhibits and that their eyes can detect,” Crawford says. “Imagine if I were bright green, but only you could see me as being bright green, but others could not.”

The molecules also serve multiple other purposes, including to help the sharks identify each other in the ocean and potentially provide protection against microbial infections, the researchers found.

While the study focused on two biofluorescent shark species, Gruber and Crawford hope to more broadly explore the bioluminescent and biofluorescent properties of marine animals, which can ultimately lead to the development of new imaging techniques.

“If you can harness the abilities that marine animals have to make light, you can generate molecular systems for imaging in the lab or in medicine. Imaging is an incredibly important biomedical objective that these types of systems could help to propel into the future,” Crawford said.

Shark numbers plummet by 92% in Australian waters

Often portrayed as a dangerous predator, the shark is suffering an unprecedented crisis.

Image credits: Terry Goss.

Sharks have been around for 425 million years — some 200 million years before dinosaurs emerged, and just before trees developed as a plant group. But their long tenure as apex predators might be coming to an end, at the hand of a regular culprit: humans.

It is estimated that 100 million sharks are killed by people every year, due to commercial and recreational fishing, and the demand for shark meat continues to rise, which puts even more pressure on their populations. A new study used information from a shark control program set in Australia in 1960. They found that the overall size of sharks has decreased — but more worryingly, the number of sharks has also dropped dramatically, in some cases by over 90%.

“What we found is that large apex sharks such as hammerheads, tigers and white sharks, have declined by 74 to 92 per cent,” said Dr. George Roff from the University of Queensland, who led the study. “And the chance of zero catch – catching no sharks at any given beach per year – has increased by as much as sevenfold.”

[panel style=”panel-default” title=”Finning” footer=””]Sharks are often killed for shark fin soup, which is considered a delicacy in some parts of the world. Fishermen capture live sharks, remove their fins with a hot metal blade, and then dump them back in the water. These immobilised sharks soon succumb to suffocation or predators.[/panel]

Hammerhead sharks, like the one depicted here, are endangered. Image credits: suneko.

Scientists also acknowledge the irony that their data was provided by a shark control program, which is preventing the recovery of vulnerable species.

Shark culls have also been carried out in Australia, the most recent one starting in 2014. The policy was ultimately cancelled in 2017 after public uproar, but the Australian government plans to re-introduce drum lines to kill sharks, using “smart” drum lines (a drum line is an unmanned aquatic trap used to lure and capture large sharks with baited hooks). Worldwide, around 80 unprovoked attacks are reported per year. Keeping in mind that we, in turn, kill 100 million of them, this is a disproportionately low figure.

While sharks are generally depicted as dangerous to humans, they serve a very important role in oceanic ecosystems. As top predators, they help to keep the ecosystem “clean”. As their numbers continue to decline, the oceans will suffer unpredictable and devastating consequences.

“Overexploitation of large apex marine predators is widespread in the world’s oceans, yet the timing and extent of declines are poorly understood,” researchers conclude. “Ongoing declines and lack of recovery of vulnerable and protected shark species are a cause for concern.”

Like all oceanic creatures, sharks are also threatened by rising water temperatures, pollution, and habitat destruction (especially around coastlines).

Journal Reference: Roff et al, “Decline of coastal apex shark populations over the past half century”, Communications Biology.

The lemon shark (Negaprion brevirostris). Credit: Wikimedia Commons.

Some sharks and rays live twice as long as we thought

Sharks and rays are among the most intensely studied marine wildlife. For some reason, though, we seem to have vastly underestimated their lifespan. According to an Australian researcher from James Cook University, some sharks and rays can live twice as long as previously estimated.

The lemon shark (Negaprion brevirostris). Credit: Wikimedia Commons.

The lemon shark (Negaprion brevirostris). Credit: Wikimedia Commons.

Dr Alastair Harry analyzed data for 53 different populations of sharks and rays finding that nearly a third of the studies which followed their lifespan had underestimated the animals’ ages. Grey nurse sharks (Carcharias taurus), can live up to 40-years-old, double the length of time first thought, and the age of New Zealand porbeagle sharks (Lamna nasus) had been underestimated by an average of 22 years, according to Harry.

To estimate the age of a shark, researchers typically count growth rings in their vertebrae. Alternatively, the measurement is confirmed by using other methods like tagging and injecting the animals with a fluorescent marker or by measuring the carbon isotopes accumulated in the animal tissue following the nuclear weapons testing of the 1950s.

“Age underestimation appears to happen because the growth rings cease to form or become unreliable beyond a certain size or age. Across the cases I studied age was underestimated by an average of 18 years, and up to 34 years in one instance. From the amount of evidence we now have it looks like the problem is systemic rather than just a few isolated cases,” Harry said in a statement.

Accurately gauging the age of marine life can be of vital importance, especially to industries involved in fishing which rely on age estimates to manage fishery stocks.

Previously, an underestimation of the orange roughy‘s lifespan led to poor fish stock productivity with long-term ecological and socio-economic impacts. Sharks and rays aren’t really sought after by fishermen but they do get caught in the net as bycatch and later are used as proxies. That means the impacts of age underestimation may well take longer to become apparent.

“It could lead to inefficient prioritisation of research, monitoring and management measures. If it’s as widespread and common as it seems from this study, the impacts could also be substantial from a wider scientific perspective, affecting the many disciplines that also use baseline life history data,” he said.

Mindblowing fact of the day: sharks are older than trees

This 240-million-year-old fish is Helicoprion. It goes to show just how much sharks have been experimenting with their arsenal. Credit: Sharkopedia.

Trees as we familiarly know them today — a primary trunk, large height, crown of leaves or fronds — didn’t appear on the planet until the late Devonian period, some 360 million years ago. You might be surprised to learn that sharks are older than trees as they’ve been around for at least 400 million years.

Sharks have been around truly for a very long time, proving their resilience. They’ve survived all five global mass extinctions that knocked 80% of the planets mega– fauna out of existence. In the worse such event, 251 million years ago, as many as 95% of species were killed.

Tracing the evolution of sharks can be frustrating. Because they have a cartilaginous skeleton, only a few body parts can be preserved as fossils, making it difficult to understand what ancient sharks were like. That’s not to say that we don’t have much to work with. Universities and museums have in their collections thousands of fossil shark scales, which are considered the most abundant of vertebrate microfossils. The most well-preserved shark fossils, however, are the teeth.

The earliest shark teeth are from early Devonian deposits, some 400 million years old, in what today is Europe. These teeth are less than an inch in length (3-4 millimeters) and belonged to an ancient shark known as Leonodus. Its double-cusped teeth suggest Leonodus may have belonged to a family of freshwater sharks known as xenacanths.

Much older shark scales have been found, though. The oldest shark-like scales date back to the late Ordovician Period, about 455 million years ago, from what is now Colorado. Such scales are different from those featured by modern sharks leading many paleontologists to dispute that these truly belonged to sharks. The oldest undisputed shark scales are about 420 million years old, from early Silurian deposits in Siberia. These diminutive survivors of prehistory have been assigned to the genus Elegestolepis, but we have no clues about what the rest of the shark might have looked like.

Sharks are sometimes called primitive but if you study them long enough you might come to see they’re very well equipped, as evidenced by 400+ million years of existence. Sharks and other elasmobranchs are very cosmopolitan, being represented by many species with different adaptations. Though many sharks like the Great White are at the top of the food chain, sharks can be found at all levels of the chain. Whether the setting is benthic, pelagic, sub-tidal, or estuarine, there is a specialized shark for that environment.

Sharks are nearly impervious to infections, cancers and circulatory diseases. They can heal and recover from severe injuries very rapidly. Some say that these features were acquired by surviving one mass extinction event after the other over the course of millions of years. Again these guys are older than freaking trees! That basically sums up how badass sharks are.

Oddly enough, despite being around for over 400 million years, sharks might have met their match: humans. Because sharks go for quality, not quantity, they have a slow rate of maturation and reproduction turn-over. But sharks are no longer apex predators in their ecosystems — humans are. Demand for shark fins is driving many species of sharks extinct, as a result. Maybe trees win the day, after all.

If you’d like to learn more and find out how you can help, visit SharkSavers.

Rotterdam’s new sharks will eat all the trash in the port’s waters

The port of Rotterdam will soon feature a new marine resident. The ‘Waste Shark,’ a drone roughly the size of your average car, will float around the port’s waters keeping an aye out for trash which it can “eat” for processing.

Put a fin on it! Image credits RanMarine.

Put a fin on it!
Image credits RanMarine.

The city of Rotterdam, Holland has been making a lot of effort in the past few years to lessen its environmental impact, and the port hasn’t been overlooked. Under the startup program PortXL, the city’s port authority has also been promoting new solutions to help make it more efficient, more sustainable, and overall just a better place. At the conclusion of the program’s first year, the port signed an agreement with South-African startup RanMarine to deploy a new drone on its waters — the Waste Shark.

The Port of Rotterdam has already announced one drone resident — the AquasmartXL, a small unmanned boat equipped with a camera that allows real-time inspection and surveillance of the water surface. But where the AquasmartXL is the eyes of Rotterdam, the Wave Shark will be its mouth. This drone is roughly the size of a car and can eat up to 500 kilograms (1102 pounds) of trash using a ‘mouth’ 35 cm under the water line. It will “fight ‘plastic soup’ at the source as 90% of all waste in the ocean starts in urban areas,” PortXL’s page reads.

https://youtu.be/J_wP74sqXos

Allard Castelein, Chief Executive Officer of the Port of Rotterdam Authority said that the Rotterdam Port Authority is determined to explore all avenues of innovation, as stated in their operational philosophy.

“Innovation cannot be forced. However, you can create an environment in which innovation is likely to take place and be in line with the market,” he said.

“We support research in conjunction with universities, such as the Port Innovation Lab with the Delft University of Technology and of course our own Erasmus University in Rotterdam. And we collaborate with contests for students. In addition, we support Dutch start-ups that are relevant to the port, but we also scout worldwide via PortXL; the first accelerator that focuses on port start-ups on a global level.”

The contract requires four Waste Sharks For to scour the waters for the next six months as part of a test run for the drones. They will operate in areas where it is too difficult, dangerous, or undesirable to use manned solutions. This includes under jetties, bridges and other structures.

Sharks usually eat meals smaller than one of yours

The voracious reputation of sharks might soon change as marine biologists uncover that most coral reef sharks eat pray smaller than a cheeseburger.

Black-tip reef shark. Image via wikimedia

Scientists from James Cook University’s ARC Centre of Excellence for Coral Reef Studies were curious to see exactly what sharks have for dinner, so they did something both awesome and yucky at the same time: they caught some, then examined the content of their stomachs to identify their last meal.

Lead author Dr. Ashley Frisch remembers that what they’d most often find was a huge chunk of nothing.

“We were surprised to find a broad range of small prey items such as fish, molluscs, sea snakes, crabs and more often than not, nothing at all,” Dr Frisch said.

“These results suggest that reef sharks eat small meals infrequently and opportunistically.”

To find out what their eating habits were over a longer period, the team conducted chemical analyses on samples of shark body tissue. The results were very surprising.

“Although black-tip, white-tip and grey reef sharks have long been thought of as top predators, we found that the chemical structure of the sharks’ body tissue actually matched closely with that of large reef fishes such as groupers, snappers and emperors,” Dr Frisch added.

“This result tells us that reef sharks and large fishes have a similar diet, but they don’t eat each other. So rather than eating big fish, reef sharks are eating like big fish.”

Co-author of the study, Dr. Justin Rizzari said that their work allows scientists to better model coral reefs food webs, and serves as a reminder that the large, conspicuous predators aren’t always the top of the food chain. Understanding ‘who eats who’ in coral reefs is important in helping scientists better predict how changes in one population impact another, allowing them to better preserve such environments.

“We now know that reef sharks are an important link in the food chain, but they are not the last link in the food chain. In most cases, the top predators are tiger sharks, hammerhead sharks, or people,” Dr Rizzari said.

“Coral reef ecosystems are very complex. The more we look, the more we realize that each and every species plays an important role. Sharks are no exception. They help to keep coral reefs healthy and should be managed wisely.”

With coral reefs around the world in decline and humans killing an estimated 100 million sharks every year, understanding the exact role sharks play in coral reef ecosystems is more urgent now than ever.

The full paper, titled “Reassessing the trophic role of reef sharks as apex predators on coral reefs” has been published online in the journal Coral Reefs, and is available here.

Armour plates and the upper and lower jaw of E. primordialis. (c) Nature

Prehistoric fish had the earliest face recognized thus far

first_face_primitive_fish

This primitive fish might be the first animal with a face. (c) Nature

A lot of complex organisms, be them long extinct like dinosaurs or still alive like mammals, present what can only be referred to as a face – a symmetrical arrangement on the head of the animal of eyes, nose and, most importantly, jaw and cheek-bones. Human are particularly adapted to recognizing faces. Thanks to our pattern solving abilities, humans have a keen talent for recognizing faces – an evolutionary treat necessary to distinguish between our peers – even in places that only look like faces (Jesus in a wood stump, human faces on Mars etc.). How did faces evolve and what animal had the first face, though?

Scientists believe the first animal currently known to us to feature what can only be called a face to be a primitive species of fish called  entelognathus primordialis (meaning “primordial complete jaw”). The fish has been dated at 419-million-years old and was found at Xiaoxiang Reservoir in Quijing, Yunnann, China. The stunning fossil was remarkably preserved for its age at the moment of discovery, helping the team of international paleontologists to determine a number of physiological characteristics. One of the first things that came to their attention was the fish’s thick exterior armor and facial bones.

Entelognathus had a rather unprepossessing face,” co-author Per Erik Ahlberg of Uppsala University told Discovery News. “The mouth was wide, the forehead low and flat, and the small, close-set and almost immobile eyes pointed forwards like a pair of car headlights.”

Jaw-dropping find puts evolution of modern face in a new light

Armour plates and the upper and lower jaw of E. primordialis. (c) Nature

Armour plates and the upper and lower jaw of E. primordialis. (c) Nature

Primitive fish older and even contemporary with e. primordialis must have looked very bizarre by today’s face-featuring standards, considering fossil records. According to Matt Friedman, a lecturer in paleobiology at the University of Oxford, these fish must have  had “broad, shovel-shaped heads with their eyes placed on top, while others had narrow bodies and skulls with their eyes on either side of the head.”  The eel-like lampreys and hagfishes, which are still alive today and which scientists commonly referred them as living fossils, are worthy examples of how these kind of prehistoric animals must have looked like.

Classic textbooks and scientific common knowledge describe the precursors to modern face-bearing animals as looking shark-like. This may be flawed information, according to the authors of the paper. The newly found prehistoric fish “puts a new face” on the original jawed species, Friedman and Brazeua write. Taking this into account, the authors revise the family tree of jawed vertebrates, showing that there is a serious possibility that the modern bony visage originated with e. primordialis’s ancestors. Sharks, it may seem, are actually more evolved organisms that retain aspects from an earlier ancestor – maybe e. primordialis itself. This would mean that humans look more like the last common ancestor of living jawed vertebrates than we thought.

“There has been a long tradition of portraying sharks as especially primitive,” Friedman said. “This is common in textbooks and documentaries that falsely claim that sharks are ‘living fossils’ and have gone unchanged for millions of years.”

It’s still unclear as to why jaw and cheek-bones appeared. A leading theory rather intuitively states that the face evolved as a superior feeding mechanism, allowing for a more flexible and adapted way of chewing on larger prey. Study co-author Brian Choo  suspects that jaws might have “evolved initially for breathing, as an apparatus to control the flow of water across the gills.”

The findings appeared in the journal Nature. [story via Discovery]

[NOW READ] Did you know there’s a fish that has human teeth? The sheepshead fish is one of a kind

This image, captured off the coast of Australia, shows a brave/stupid marine biologist who managed to touch a great white as it leapt out of the water. (C) mirror.co.uk

What’s the chance of being attacked by a shark – the hard numbers

 This image, captured off the coast of Australia, shows a brave/stupid marine biologist who managed to touch a great white as it leapt out of the water. (C) mirror.co.uk

This image, captured off the coast of Australia, shows a brave/stupid marine biologist who managed to touch a great white as it leapt out of the water. (C) mirror.co.uk

It’s summer, so beach season is naturally in full swing. A lot of people diving trough coastal areas in the Atlantic and Pacific are worried, however, of being attacked by sharks. So, what are the chances of being attacked by one? In short: really, really slim.

Popular Hollywood flicks like Jaws and its sequels, as well as a sort of deeply rooted anti-shark culture induced by fear (white sharks are considered terrifying by many, and are thus attributed with more credit than justly due), have led to a skewed portrayal of the real risks sharks pose.

While every year there are a number of reported shark attacks, when compared to the actual number of people that actually visit the beaches by the millions, these reports should not bother the casual swimmer if viewed with reason first. For instance, last year, 80 unprovoked shark strikes took place worldwide: Seven resulted in deaths, including one in California. Fifty-three strikes took place in U.S. waters, nearly half of them off Florida according to the International Shark Attack File at the Florida Museum of Natural History.

In the year 2000, just one person died as a result of shark attacks, meaning at the time the beachgoer faced a 1-in-11.5-million chance of being attacked by a shark, and less than a 1-in-264-million chance of dying from a shark bite. In contrast,  beachgoers faced a 1-in-2-million chance of dying from drowning and other causes based on visits to East and West Coast beaches. Here are more numbers: more Americans were killed by collapsing sinkholes (16) than sharks (11) between 1990 and 2006, and more by tornadoes (125) than sharks (6) in Florida between 1985 and 2010.

It’s worth noting, however, that these number might be themselves a bit misleading. Some areas are definitely more prone to attacks than others, like is the case of Florida, and in recent years the number of beach shark sightings have significantly increased. Last year, there were more than 20 confirmed shark sightings at Cape Cod beaches, while this summer some eight sightings were made – consider, however, that the same shark may be responsible for multiple sightings.

The National Park Service has thus issued strict warnings in areas at risk such as Cape Cod, so if you’re hitting the beach be on the look out for such warnings – they’re easy to spot nevertheless. Part of the reason these sightings have increased is the dramatic upsurge in seal populations, which have swelled by the thousands thanks to conservation efforts since the enactment of the Marine Mammal Protection Act. White sharks, as well as other species, have seal as a favorite course on their menu. With this in mind, where you’ll find seals, there’s a big chance sharks aren’t too far out.

Currently, researchers like those at the National Park Service are actively pursuing sharks that go near beaches and tag them. Using modern technology (satellite and radio tagging), shark swimming patterns are now typically well layered out so that humans get to interact with them as rarely as possible.

[RELATED] Sharks worth more money alive in the ocean than in a soup bowl, study finds

Given the extremely slim chances of being attacked, let alone killed, by a shark, it’s rather ironic that humans have such a great fear of sharks considering millions of sharks are killed every year at our hand. French Polynesia and the Cook Islands joined together to create the world’s largest shark sanctuary, emulating small island nations such as Palau and the Maldives in banning all shark fishing in their waters. In the rest of the world, however, sharks are still hunted down and killed by the millions with little to any intervention from regularity agencies.

dogfish squalamine

Shark anti-virus compound could cure deadly infections in humans

dogfish squalamineIn 1993 Michael Zasloff, of the Georgetown University Medical Center, discovered an incredible compound inside the tissue dogfish sharks (Squalus acanthus), called squalamine, which has the remarkable property of shielding sharks from viral infections by preventing them from multiplying. Almost ten years later, further research shows that the compound might provide effective treatment and even cure terribly infectious diseases in the human body as well.

Squalamine works its magic by interrupting the life cycle of viruses, preventing it from replicating. Currently, the compound is known to block viral infections such as such as dengue fever and hepatitis, both very hard to treat  for humans.

“It’s a whole new approach to treatment of viral disease,” said study leader Michael Zasloff, of the Georgetown University Medical Center.

“It’s very possible we could cure several diseases we [now] treat as chronic infections.”

Zasloff was initially looking for anti-bacterial agents in sharks, before he eventually stumbled across the miracle squalamine. He soon found that it actually inhibits the growth of blood vessels, suggesting the molecule could potentially stop cancer cells from multiplying. Squalamine molecules stick to a cell’s membrane, and in the process disrupts positively charged proteins initially in place on the membrane. When a virus invades, it needs those protein to reproduce, without them it dies.

“There is no other compound known to science that does this—this is a remarkable property,” Zasloff said.

The shark’s “antiviral defenses have been extraordinary,” Zasloff said. “It has adapted a very remarkable immune system and stayed with

According to Zasloff, squalamine might just be the secret to the shark’s remarkable evolution and survival for the past hundreds of millions of years.

Squalamine might treat terrible diseases in humans

Tests revealed that squalamine thwarted infection of the dengue fever virus in human blood vessel cells and of hepatitis B and D in human liver cells. The study goes on to claim that squalamine inhibited yellow fever, eastern equine encephalitis virus, and murine cytomegalovirus in lab animals.

The results are incredible and look extremely promising for the development of a squalamine based super-drug in the future. This won’t hold any repercussions back to sharks either, since squalamine has been successfully synthesized since 1995.

Apparently, there are some toxic side effects to the substance when a treatment dose is administered, but further research might render these effects to a safe margin. Cinical trials for the antiviral will begin in people in about a year.

Sharks have been hiding squalamine in their bodies for 700 million years, Zasloff added. “Now it’s a gift to us.”

National Geographic