First-ever sighting of a live newborn great white

Great whites, the largest predatory sharks in the world with the most fatal attacks on humans, are tough to imagine as newborn babies. That is partially because no one has seen one in the wild, it seems, until now.

Wildlife filmmaker Carlos Gauna and UC Riverside biology doctoral student Phillip Sternes were scanning the waters for sharks on July 9, 2023, near Santa Barbara on California's central coast.

That day, something exciting appeared on the viewfinder of Gauna's drone camera.

It was a shark pup unlike any they'd ever seen.

Great whites, referred to only as white sharks by scientists, are gray on top and white on the bottom.

But this roughly 5-foot-long shark was pure white.

"We enlarged the images, put them in slow motion, and realized the white layer was being shed from the body as it was swimming," Sternes said.

"I believe it was a newborn white shark shedding its embryonic layer."

These observations are documented in a new paper in the Environmental Biology of Fishes journal.

The paper also details the significance of having seen a live newborn white shark.

Gauna is known online as The Malibu Artist. He has spent thousands of hours filming sharks around the world, and his videos of them swimming close to beachgoers have millions of views.

What he and Sternes observed could help solve the longstanding mystery of great white birthing habits.

"Where white sharks give birth is one of the holy grails of shark science. No one has ever been able to pinpoint where they are born, nor has anyone seen a newborn baby shark alive," Gauna said.

"There have been dead white sharks found inside deceased pregnant mothers. But nothing like this."

Though the paper authors acknowledge it is possible the white film the shark shed could have been a skin condition, the duo do not believe this to be the case.

"If that is what we saw, then that too is monumental because no such condition has ever been reported for these sharks," Gauna said.

For many reasons, the duo believes what they saw was in fact a newborn great white.

First, great white females give birth to live pups. While in utero, the embryonic sharks might feed on unfertilized eggs for protein.

The mothers offer additional nourishment to the growing shark pups with a 'milk' secreted in the uterus.

"I believe what we saw was the baby shedding the intrauterine milk," Sternes said.

A second reason is the presence of large, likely pregnant great whites in this location.

Gauna had observed them here in previous years, and in the weeks leading up to the observation.

"I filmed three very large sharks that appeared pregnant at this specific location in the days prior. On this day, one of them dove down, and not long afterwards, this fully white shark appears," Gauna said.

"It's not a stretch to deduce where the baby came from."

Thirdly, the shark's size and shape are also indicative of a newborn.

What the two observed was thin, short, and rounded. "In my opinion, this one was likely hours, maybe one day old at most," Sternes said.

Finally, this location off the coast of central California has long been proposed as a birthing location for great whites.

"There are a lot of hypothetical areas, but despite intense interest in these sharks, no one's seen a birth or a newborn pup in the wild," Sternes said.

"This may well be the first evidence we have of a pup in the wild, making this a definitive birthing location."

Many scholars believe great whites are born farther out at sea.

That this pup was filmed so close to shore -- roughly 1,000 feet from the beach -- is significant because its age means it was likely born in shallow waters.

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The megalodon was less mega than previously believed

A new study shows the Megalodon, a gigantic shark that went extinct 3.6 million years ago, was more slender than earlier studies suggested. This finding changes scientists’ understanding of Megalodon behavior, ancient ocean life, and why the sharks went extinct.

The Megalodon or megatooth shark is typically portrayed as a super-sized monster in popular culture, with recent examples in the sci-fi films “The Meg” (2018) and “Meg 2: The Trench” (2023). Previous studies assume that the shark likely reached lengths of at least 50 feet and possibly as much as 65 feet.

However, the Megalodon is largely known only from its teeth and vertebrae in the fossil record — a rather incomplete set of data from which to draw assumptions.

Thus, the modern great white shark was traditionally used as a model for Megalodon bodies in previous studies.

That model led researchers to conclude that the shark was round and stocky like great whites.

“Our team reexamined the fossil record, and discovered the Megalodon was more slender and possibly even longer than we thought. Therefore, a better model might be the modern mako shark,” said UCR biologist and paper first author Phillip Sternes.

“It still would have been a formidable predator at the top of the ancient marine food chain, but it would have behaved differently based on this new understanding of its body.”

For the new study published in the journal Palaeontologia Electronica, a team of 26 scientists from around the world, co-led by Sternes and DePaul University paleobiology professor Kenshu Shimada, was inspired by differences in previously estimated body lengths for the Megalodon.

“It was a ‘eureka-moment’ when our research team realized the discrepancy between two previously published lengths for the same Megalodon specimen,” said Shimada.

The team then weighed in on a new comparison of Megalodon vertebra fossils to those of living lamniform shark relatives.

“We measured the whole vertebral skeleton of a living great white shark with a CT scanner and compared that to the previous reconstruction of the Megalodon vertebral column,” Sternes said.

“It was still a giant, predatory shark. But the results strongly suggest that the Megalodon was not merely a larger version of the modern great white shark.”

A revised understanding of the Megalodon body type would in turn affect scientists’ understanding not only of the giant shark itself, but also of its impact on the ecology and evolution of marine ecosystems that shaped the present-day oceans.

There is no doubt the Megalodon is one of the largest marine predators ever to have lived.

But a slimmer and more elongated body would suggest the Megalodon also had a longer digestive canal.

Sternes explained that in this case, the sharks might have enjoyed enhanced absorption of nutrients, and may not have had to eat as often as previously believed.

“With increased ability to digest its food, it could have gone for longer without needing to hunt. This means less predation pressure on other marine creatures,” Sternes said.

“If I only have to eat one whale every so often, whale populations would remain more stable over time.”

Some shark scientists have theorized that a natural decrease in prey led to the extinction of Megalodons.

However, Sternes has another theory, in part supported by the revised understanding of its shape.

“I believe there were a combination of factors that led to the extinction, but one of them may have been the emergence of the great white shark, which was possibly more agile, making it an even better predator than the Megalodon,” Sternes said.

“That competition for food may have been a major factor in its demise.”

The research team of shark experts from the U.S., UK, Austria, France, Japan, Mexico, Brazil, and Australia all feel that a revised understanding of ancient marine life would have a cascading effect on the oceans that are still visible today.

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This Japanese 'dragon' terrorized ancient seas

Researchers have described a Japanese mosasaur the size of a great white shark that terrorized Pacific seas 72 million years ago.

Extra-long rear flippers might have aided propulsion in concert with its long finned tail.

And unlike other mosasaurs, or large extinct marine reptiles, it had a dorsal fin like a shark's that would have helped it turn quickly and with precision in the water.

University of Cincinnati Associate Professor Takuya Konishi and his international co-authors described the mosasaur and placed it in a taxonomic context in the Journal of Systematic Palaeontology.

The mosasaur was named for the place where it was found, Wakayama Prefecture.

Researchers call it the Wakayama Soryu, which means blue dragon.

Dragons are creatures of legend in Japanese folklore, Konishi said.

"In China, dragons make thunder and live in the sky. They became aquatic in Japanese mythology," he said.

The specimen was discovered along the Aridagawa River in Wakayama by co-author Akihiro Misaki in 2006.

The specimen is the most complete skeleton of a mosasaur ever found in Japan or the northwestern Pacific, Konishi said.

"In this case, it was nearly the entire specimen, which was astounding," Konishi said.

He has dedicated his career to studying these ancient marine reptiles.

But the Japanese specimen has unique features that defies simple classification, he said.

Its rear flippers are longer than its front ones. These enormous flippers are even longer than its crocodile-like head, which is unique among mosasaurs.

"I thought I knew them quite well by now," Konishi said. "Immediately it was something I had never seen before."

Mosasaurs were apex predators in prehistoric oceans from about 100 million years ago to 66 million years ago.

They were contemporaries of Tyrannosaurus rex and other late Cretaceous dinosaurs that ruled the Earth.

Mosasaurs were victims of the same mass extinction that killed off nearly all dinosaurs when an asteroid struck what is now the Gulf of Mexico.

Researchers placed the specimen in the subfamily Mosasaurinae and named it Megapterygius wakayamaensis to recognize where it was found.

Megapterygius means "large winged" in keeping with the mosasaur's enormous flippers.

Konishi said those big paddle-shaped flippers might have been used for locomotion.

But that type of swimming would be extraordinary not only among mosasaurs but among virtually all other animals.

"We lack any modern analog that has this kind of body morphology -- from fish to penguins to sea turtles," he said.

"None has four large flippers they use in conjunction with a tail fin."

Researchers speculated that the large front fins might have helped with rapid maneuvering while its large rear fins might have provided pitch to dive or surface.

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Evolution of taste: Early sharks were able to perceive bitter substances

A research team from the University of Cologne, in collaboration with colleagues from the Leibniz Institute for Food Systems Biology in Freising, has discovered a receptor for bitter taste in twelve different cartilaginous fish (sharks and rays). The receptor belongs to the so-called taste receptors type 2 (T2R), which also make humans perceive bitter and potentially toxic foods. Until now, it was assumed that such receptors only occur in bony vertebrates. The work was published under the title 'A singular shark bitter taste receptor provides insights into the evolution of bitter taste perception' in the journal Proceedings of the National Academy of Sciences (PNAS).

In the past, molecular research has had limited information on sharks, as their genomes are often relatively large. Therefore, sequencing is often more complex and takes longer than with many other animals. However, the techniques are more advanced nowadays, providing ever more information on the gene sequences of many cartilaginous fishes. This enabled the neurobiologists lecturer (Privatdozent) Dr Maik Behrens and Tatjana Lang from the Leibniz Institute for Food Systems Biology and Professor Dr Sigrun Korsching at the Institute of Genetics of the University of Cologne to specifically search for bitter taste receptors in cartilaginous fish.

Twelve out of seventeen cartilaginous fish genomes studied contained genes for the taste receptors type 2, with only one T2R gene present in each species. The researchers named this single gene T2R1. The fact that only a single T2R gene was found suggests that it is the original form of these bitter taste receptors, which was not altered by gene duplication and subsequent different specialization of the resulting receptors.

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Why a surprising discovery, warming seas and the demise of the 'Meg' may spell trouble for more and more sharks

Some unexpected shark strandings and subsequent surprises following autopsies have, ironically, taken marine biologists millions of years back in time as they look to the future with concern. Adding chapters to an evolutionary tale involving the infamous megalodon shark (the "Meg"), they think their work suggests there are more warm-blooded sharks out there than previously believed, and -- based on the Meg's demise -- these species may be at great risk from warming seas.

Some of the most famous sharks, like the white shark or the extinct megalodon, are unusual in being among the mere ~1% of shark species to be considered warm-blooded or "regional endotherms."

It had always been thought warmer muscles help fish be powerful and athletic, with regional endothermy only seen in apex predators like the great white or giant tuna. But there has also been some debate about when regional endothermy evolved, and whether extinct species like the megalodon was warm bodied.

In a new study led by Trinity College Dublin, researchers have found that a relatively ancient (but still-living) shark species -- the smalltooth sand tiger, thought to have diverged from the Meg at least 20 million years ago -- has anatomic features suggesting it is a regional endotherm. Coming hot on the fins of a similar shock that slow-moving, filter-feeding basking sharks are also regional endotherms, the researchers now believe there are more warm-blooded sharks than science thought, and that warm bloodedness evolved quite a long time ago.

Dr Nicholas Payne from Trinity's School of Natural Sciences was senior author of the study, published this week in Biology Letters. He said:

"We think this is an important finding, because if sand tiger sharks have regional endothermy then it's likely there are several other sharks out there that are also warm-bodied.

"We used to think regional endothermy was confined to apex predators like the great white and extinct megalodon, but now we have evidence that deep water 'bottom dwelling' sand tigers, and plankton-eating basking sharks also are warm bodied. This raises plenty of new questions as to why regional endothermy evolved, but it might also have important conservation implications."

The research team (including scientists from University of Pretoria, ZSL, University of Zurich, Swansea University, Smithsonian Tropical Research Institute and University College Dublin College of Agriculture Food Science and Veterinary Medicine) undertook dissections of dead smalltooth sand tiger sharks that washed up in Ireland and the UK in making their discoveries.

Dr Haley Dolton, also from Trinity, was lead author of the study. She said:

"Our understanding of science continually grows and it's becoming clear that whenever regional endothermy evolved in the past it has been retained in a growing number of shark species with very different life styles. When we first realised that the smalltooth tigers have traits associated with regional endotherms I thought 'here we go again!', but the next time we see it in another species I might be a little less shocked.

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New 3D model shows: Megalodon could eat prey the size of entire killer whales

Megalodon, the largest shark that ever lived, is famous for its huge, human-hand-sized teeth. However, there is little fossil evidence of its whole body. International researchers in collaboration with UZH used an exceptionally preserved specimen to create a 3D computer model of its full body. Their results suggest that the megalodon could fully consume prey the size of today's killer whales and then roam the seas without more food for two months.

The reconstructed megadolon (Otodus megalodon)was 16 meters long and weighed over 61 tons. It was estimated that it could swim at around 1.4 meters per second, require over 98,000 kilo calories every day and have stomach volume of almost 10,000 liters. These results suggest that the megalodon could travel long distances and was capable of eating whole prey of up to 8 meters long. This is notably the size of modern killer whales, today's top ocean predator. An ability to eat large apex predators of comparable size millions of years ago places megalodon at a higher trophic level than modern top predators.

Well-preserved spine enables reconstruction

These are the findings of an international study carried out in collaboration with the University of Zurich. The research was only possible thanks to the 3D modelling of one individual megalodon which was discovered in the 1860s. Against all odds, a sizeable portion of its vertebral column was left behind in the fossil record after the creature died in the Miocene oceans of Belgium at the age of 46 about 18 million years ago.

"Shark teeth are common fossils because of their hard composition which allows them to remain well preserved," says first author Jack Cooper, PhD student at Swansea University. "However, their skeletons are made of cartilage, so they rarely fossilize. The megalodon vertebral column from the Royal Belgian Institute of Natural Sciences is therefore a one-of-a-kind fossil."

From single vertebra to whole body mass

The research team, which includes researchers from Switzerland, UK, USA, Australia and South Africa, first measured and scanned every single vertebra, before reconstructing the entire column. They then attached the column to a 3D scan of a megalodon's dentition from the United States. They completed the model by adding "flesh" around the skeleton using a 3D-scan of the body of a great white shark from South Africa.

"Weight is one of the most important traits of any animal. For extinct animals we can estimate the body mass with modern 3D digital modelling methods and then establish the relationship between mass and other biological properties such as speed and energy usage," says co-author John Hutchinson, professor at the Royal Veterinary College in the UK.

A trans-oceanic super-apex predator

The high energetic demand would have been met by feeding on calorie-rich blubber of whales, in which megalodon bite marks have previously been found in the fossil record. An optimal foraging model of potential megalodon prey encounters found that eating a single 8-meter-long whale may have allowed the shark to swim thousands of miles across oceans without eating again for two months. "These results suggest that this giant shark was a trans-oceanic super-apex predator," says Catalina Pimiento, Professor at the University of Zurich and senior author of the study. "The extinction of this iconic giant shark likely impacted global nutrient transport and released large cetaceans from a strong predatory pressure."

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What are whale sharks up to?

The largest fish in the ocean is a globe-trotter that can occasionally be found basking in the coastal waters of the Panamanian Pacific. However, little more is known about the habits of the whale shark (Rhincodon typus) in the region. By satellite-tracking the whereabouts of 30 of them, scientists from the Smithsonian Tropical Research Institute (STRI), the Anderson Cabot Center for Ocean Life and the University of Panama explored the factors influencing this endangered species' behavior.

The R. typus, like other large sharks, may take years or even decades to reach maturity and reproduce, making them vulnerable to population declines, especially when combined with human threats. For instance, they may be caught in fishing nets as bycatch or face the risk of vessel strikes when shipping lanes overlap with their feeding sites. Being able to understand and predict whale shark behavior is a necessary step for protecting the species.

The satellite monitoring of this species, led by STRI marine ecologist Héctor Guzmán, found that whale sharks feed mainly in coastal waters, seamounts and ridges of the Panamanian Pacific, where they can find an abundance of their favorite foods: small fish and plankton. They were also spotted swimming north and southbound along the coast, towards Mexico and Ecuador, and towards the open ocean to feed.

"This species requires clear regional planning," said Guzmán. "Once the feeding and breeding aggregation areas are identified, some protection measures should be implemented. The newly announced marine protected area expansions across the region provide an interesting platform for large-scale conservation practices."

Although they used marine protected areas, the whale sharks also spent time in industrial fishing and vessel traffic zones, which could endanger them according to the new article published in Frontiers in Marine Science.

"The study shows how complex it is to protect whale sharks: tagged individuals visited 17 marine protected areas in 5 countries, but more than 77% of their time they were in areas without any protection," said Catalina Gómez, co-author of the study and marine ecologist at the University of Panama.

Thus, for highly migratory and endangered species such as the whale shark, conservation measures should go beyond the establishment of local marine protected areas.

Efforts should focus on protecting large oceanic areas and establishing marine corridors that transcend national borders, for example: the newly expanded Cordillera de Coiba Marine Protected Area in Panama or the Marine Conservation Corridor of the Eastern Tropical Pacific which connects Coiba with Costa Rica's Cocos Islands, the Galapagos in Ecuador and Colombia's Malpelo Island.

"A periodic tagging program should continue for two main reasons: first, we still don't know where the species reproduces and tracking may lead us in the right direction," said Guzmán. "Second, we know that they are moving across extensive areas. We have identified potential corridors or seaways, as well as aggregation areas, that require management attention and clear protection rules. Tracking will allow us to better identify those regional routes."

The satellite tracking also revealed a whale shark migratory pattern that seems to be associated with circular ocean currents called eddies.

"Eddies are recognized as potential feeding areas for migratory species or food epicenters in the oceans, so they can swim in those areas for a long time while foraging and feeding," said Guzman. "However, eddies are dynamic systems and change constantly in speed or strength, size and location, even seasonally. These feeding areas are important for conservation, especially considering their dynamics and potential changes associated with climate change."

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What did Megalodon eat? Anything it wanted -- including other predators.

New Princeton research shows that prehistoric megatooth sharks -- the biggest sharks that ever lived -- were apex predators at the highest level ever measured.

Megatooth sharks get their name from their massive teeth, which can each be bigger than a human hand. The group includes Megalodon, the largest shark that ever lived, as well as several related species.

While sharks of one kind or another have existed since long before the dinosaurs -- for more than 400 million years -- these megatooth sharks evolved after the dinosaurs went extinct and ruled the seas until just 3 million years ago.

"We're used to thinking of the largest species -- blue whales, whale sharks, even elephants and diplodocuses -- as filter feeders or herbivores, not predators," said Emma Kast, a 2019 Ph.D. graduate in geosciences who is the first author on a new study in the current issue of Science Advances. "But Megalodon and the other megatooth sharks were genuinely enormous carnivores that ate other predators, and Meg went extinct only a few million years ago."

Her adviser Danny Sigman, Princeton's Dusenbury Professor of Geological and Geophysical Sciences, added, "If Megalodon existed in the modern ocean, it would thoroughly change humans' interaction with the marine environment."

A team of Princeton researchers has now discovered clear evidence that Megalodon and some of its ancestors were at the very highest rung of the prehistoric food chain -- what scientists call the highest "trophic level." Indeed, their trophic signature is so high that they must have eaten other predators and predators-of-predators in a complicated food web, say the researchers.

"Ocean food webs do tend to be longer than the grass-deer-wolf food chain of land animals, because you start with such small organisms," said Kast, now at the University of Cambridge, who wrote the first iteration of this research as a chapter in her dissertation. "To reach the trophic levels we're measuring in these megatooth sharks, we don't just need to add one trophic level -- one apex predator on top of the marine food chain -- we need to add several onto the top the modern marine food web."

Megalodon has been conservatively estimated at 15 meters long -- 50 feet -- while modern great white sharks typically top out around five meters (15 feet).

To reach their conclusions about the prehistoric marine food web, Kast, Sigman and their colleagues used a novel technique to measure the nitrogen isotopes in the sharks' teeth. Ecologists have long known that the more nitrogen-15 an organism has, the higher its trophic level, but scientists have never before been able to measure the tiny amounts of nitrogen preserved in the enamel layer of these extinct predators' teeth.

"We have a series of shark teeth from different time periods, and we were able to trace their trophic level versus their size," said Zixuan (Crystal) Rao, a graduate student in Sigman's research group and a co-author on the current paper.

One way to tuck in an extra trophic level or two is cannibalism, and several lines of evidence point to that in both megatooth sharks and other prehistoric marine predators.

The nitrogen time machine

Without a time machine, there's no easy way to recreate the food webs of extinct creatures; very few bones have survived with teeth marks that say, "I was chewed on by a massive shark."

Fortunately, Sigman and his team have spent decades developing other methods, based on the knowledge that the nitrogen isotope levels in a creature's cells reveal whether it is at the top, middle or bottom of a food chain.

"The whole direction of my research team is to look for chemically fresh, but physically protected, organic matter -- including nitrogen -- in organisms from the distant geologic past," said Sigman.

A few plants, algae and other species at the bottom of the food web have mastered the knack of turning nitrogen from the air or water into nitrogen in their tissues. Organisms that eat them then incorporate that nitrogen into their own bodies, and critically, they preferentially excrete (sometimes via urine) more of nitrogen's lighter isotope, N-14, than its heavier cousin, N-15.

In other words, N-15 builds up, relative to N-14, as you climb up the food chain.

Other researchers have used this approach on creatures from the recent past -- the most recent 10-15 thousand years -- but there hasn't been enough nitrogen left in older animals to measure, until now.

Why? Soft tissue like muscles and skin are hardly ever preserved. To complicate matters, sharks don't have bones -- their skeletons are made of cartilage.

But sharks do have one golden ticket into the fossil record: teeth. Teeth are more easily preserved than bones because they are encased in enamel, a rock-hard material that is virtually immune to most decomposing bacteria.

"Teeth are designed to be chemically and physically resistant so they can survive in the very chemically reactive environment of the mouth and break apart food that can have hard parts," Sigman explained. And in addition, sharks aren't limited to the 30 or so pearly whites that humans have. They are constantly growing and losing teeth -- modern sand sharks lose a tooth every day of their decades-long lives, on average -- which means that every shark produces thousands of teeth over its lifetime.

"When you look in the geologic record, one of the most abundant fossil types are shark teeth," said Sigman. "And within the teeth, there is a tiny amount of organic matter that was used to build the enamel of the teeth -- and is now trapped within that enamel."

Since shark teeth are so abundant and are preserved so well, the nitrogen signatures in enamel provide a way to measure status in the food web, whether the tooth fell from a shark's mouth millions of years ago or yesterday.

Even the largest tooth has only a thin casing of enamel, of which the nitrogen component is only a tiny trace. But Sigman's team has been developing more and more refined techniques for extracting and measuring these nitrogen isotope ratios, and with a little help from dentist drills, cleaning chemicals and microbes that ultimately convert the nitrogen from within the enamel into nitrous oxide, they're now able to precisely measure the N15-N14 ratio in these ancient teeth.

"We're a little bit like a brewery," he said. "We grow microbes and feed our samples to them. They produce nitrous oxide for us, and then we analyze the nitrous oxide they produced."

The analysis requires a custom-built, automated nitrous oxide preparation system that extracts, purifies, concentrates and delivers the gas to a specialized stable isotope ratio mass spectrometer.

"This has been a multiple-decades-long quest that I've been on, to develop a core method to measure these trace amounts of nitrogen," Sigman said. From microfossils in sediments, they moved on to other types of fossils, like corals, fish ear bones and shark teeth. "Next, we and our collaborators are applying this to mammalian teeth and dinosaur teeth."

A deep dive into the literature during lockdown

Early in the pandemic, while her friends were making sourdough starters and bingeing Netflix, Kast pored through the ecologic literature to look for nitrogen isotope measurements of modern marine animals.

"One of the cool things that Emma did was really dig into the literature -- all the data that's been published over decades -- and relate that to the fossil record," said Michael (Mick) Griffiths, a paleoclimatologist and geochemist at William Patterson University and a co-author on the paper.

As Kast quarantined at home, she painstakingly built up a record with more than 20,000 marine mammal individuals and more than 5,000 sharks. She wants to take things much further. "Our tool has the potential to decode ancient food webs; what we need now is samples," said Kast. "I'd love to find a museum or other archive with a snapshot of an ecosystem -- a collection of different kinds of fossils from one time and place, from forams near the very base of the food web, to otoliths -- inner ear bones -- from different kinds of fish, to teeth from marine mammals, plus shark teeth. We could do the same nitrogen isotope analysis and put together the whole story of an ancient ecosystem."

In addition to the literature search, their database includes their own samples of shark teeth. Co-author Kenshu Shimada of DePaul University connected with aquariums and museums, while co-authors Martin Becker of William Patterson University and Harry Maisch of Florida Gulf Coast University gathered megatooth specimens on the sea floor.

Read more at Science Daily

Jaws hold crucial knowledge on the fate of sharks

Jaws was the only word needed to give the iconic 1970's thriller about a great white with a preference for humans its eerie title. Though a strong and important player at the top of the foodchain, sharks face a range of enemies: overfishing, habitat loss, pollution and climate change and human fear resulting in the use of shark control programs in some locations.

The fear and fascination for sharks have made people collect shark jaws for decades. These collections of shark jaws from museums, national fishery institutes and personal collections, including modern samples from fishery institutes represent a great opportunity for scientists.

Using genomic data retrieved from historical tiger shark jaws, an international group of scientists including Professor Einar Eg from the Technical University of Denmark has found evidence of the disappearance of a local southeastern Australian population of tiger sharks. A disappearance associated with a documented local decline in abundance of tiger sharks, likely caused by the ongoing shark control program.

The international study Retrospective genomics highlights changes in genetic composition of tiger sharks (Galeocerdo cuvier) and potential loss of a south-eastern Australia population has just been published in the journal Scientific Reports

"Our study shows that tiger sharks can have local and genetically isolated populations at a restricted geographical scale -- such as the south Eastern Australian coast -- and that these local populations are vulnerable to direct exploitation and shark control programs," says Einar Eg.

Top predator controls the ecosystem balance

The study shows that there are still tiger sharks in the area. However, these individuals belong to an, apparently, more widespread population found across the east/north coast of Australia.

"When we, through genetic analysis, better understand the distribution and migration of shark populations and their responses to human activities over historical time, we are better able to design proper management plans and actions at the appropriate geographical scale. Not only for the benefit of sharks, but for marine ecosystems as a whole," says Einar Eg and explains:

"Sharks are top predators. They control the abundance of other species below them, and sick fish, in the food chain, ensuring species diversity. I.e. they are important for maintaining ecosystem balance. They are generally long lived and slow reproducers, so a healthy shark fauna signals a healthy ocean and ecosystem."

Genetic diversity is the fuel that drives future evolution

Before the new study, it was believed that tiger sharks did not display local population structure. Thus, genetic differences among tiger shark populations were only found at a basin wide scale, such as between tiger sharks in the Pacific and Atlantic oceans. Accordingly, tiger sharks were expected to display low vulnerability towards local depletion. Therefore management of the species at a large geographical scale was in focus.

"From our samples alone, it appears that the historical local population has been extirpated or significantly reduced. This means that management of the species also has to focus on regional processes and exploitation patterns in order to protect local populations and biodiversity of the species as a whole," says Einar Eg and points to the crucial aspects of genetic research:

"Genetic diversity within a species, is the fuel that drives future evolution and adaptation to the environment, e.g. climate change. Without historical genetic/genomic data, there is no way of assessing the loss of genetic diversity within a species."

Fear and facts -- are sharks moving North?

With regards to the shark control programs having an impact on shark numbers, the obvious question arises "How afraid should one actually be to go swimming in Australia or South Africa?"

"In 2021, there were 73 cases of unprovoked shark bites worldwide, with a total of 11 fatalities. Most attacks were related to surfing and board sports. In Australia, there were three fatalities and 1 in SA. So, the chance of being attacked and killed by a shark is almost non-existing. One should definitely be more afraid of driving in your car writing txt messages," says Einar Eg.

As climate change causes sea temperatures to rise, some researchers say that we may be looking into a future with large sharks entering Danish/European waters. However, Einar Eg stresses that though changed temperature conditions could allow for more large sharks occurring in Danish/European waters, many other factors determine the distribution of a species.

"The Mediterranean, for instance, is very suitable for large sharks, but we do not see large assemblages of white, tiger, mako sharks there. If they come, it is highly unlikely that this would result in any bather-shark conflicts. As an example, there were no reported shark bites in Europe for 2021," says Einar Eg.

A future for sharks

On a global scale, the tiger shark is near threatened. According to Professor Einar Eg that covers a significant species depletion in some areas, while they're doing ok in other regions of the world: "We need to shift tiger shark management conceptually from an exclusive species view to also include the local population aspect. I.e. saving global populations has to go through protection and proper management of local populations," says Einar Eg.

"Now, by having our temporal genetic data, we can study the genetic impact of anthropogenic pressure on marine species, enabling us to improve management in order to secure biodiversity."

How can genetic research continue and help improve shark control and hunting in favour of sharks?

"Genetic research can help to elucidate the proper biological units (genetic populations), which should be the target for fisheries management, conservation and biodiversity protection," says Einar Eg and concludes:

"Studies like ours can illustrate the likely consequences of local over-exploitation in relation to shark control and make us realize what we can lose by not paying attention to the distribution of genetic variation within a species."

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Sharks use Earth's magnetic fields to guide them like a map

Sea turtles are known for relying on magnetic signatures to find their way across thousands of miles to the very beaches where they hatched. Now, researchers reporting in the journal Current Biology on May 6 have some of the first solid evidence that sharks also rely on magnetic fields for their long-distance forays across the sea.

"It had been unresolved how sharks managed to successfully navigate during migration to targeted locations," said Save Our Seas Foundation project leader Bryan Keller, also of Florida State University Coastal and Marine Laboratory. "This research supports the theory that they use the earth's magnetic field to help them find their way; it's nature's GPS."

Researchers had known that some species of sharks travel over long distances to reach very specific locations year after year. They also knew that sharks are sensitive to electromagnetic fields. As a result, scientists had long speculated that sharks were using magnetic fields to navigate. But the challenge was finding a way to test this in sharks.

"To be honest, I am surprised it worked," Keller said. "The reason this question has been withstanding for 50 years is because sharks are difficult to study."

Keller realized the needed studies would be easier to do in smaller sharks. They also needed a species known for returning each year to specific locations. He and his colleagues settled on bonnetheads (Sphyrna tiburo).

"The bonnethead returns to the same estuaries each year," Keller said. "This demonstrates that the sharks knows where 'home' is and can navigate back to it from a distant location."

The question then was whether bonnetheads managed those return trips by relying on a magnetic map. To find out, the researchers used magnetic displacement experiments to test 20 juvenile, wild-caught bonnetheads. In their studies, they exposed sharks to magnetic conditions representing locations hundreds of kilometers away from where the sharks were actually caught. Such studies allow for straightforward predictions about how the sharks should subsequently orient themselves if they were indeed relying on magnetic cues.

If sharks derive positional information from the geomagnetic field, the researchers predicted northward orientation in the southern magnetic field and southward orientation in the northern magnetic field, as the sharks attempted to compensate for their perceived displacement. They predicted no orientation preference when sharks were exposed to the magnetic field that matched their capture site. And, it turned out, the sharks acted as they'd predicted when exposed to fields within their natural range.

The researchers suggest that this ability to navigate based on magnetic fields may also contribute to the population structure of sharks. The findings in bonnetheads also likely help to explain impressive feats by other shark species. For instance, one great white shark was documented to migrate between South Africa and Australia, returning to the same exact location the following year.

"How cool is it that a shark can swim 20,000 kilometers round trip in a three-dimensional ocean and get back to the same site?" Keller asked. "It really is mind blowing. In a world where people use GPS to navigate almost everywhere, this ability is truly remarkable."

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Older than expected: Teeth reveal the origin of the tiger shark

With a total length of up to 5.5m, the tiger shark is one of the largest predatory sharks known today. This shark is a cosmopolitan species occurring in all oceans worldwide. It is characterized by a striped pattern on its back, which is well marked in juveniles but usually fades in adults.

An international team of researchers led by Julia Türtscher from the University of Vienna examined the fossil record of these apex predators and found out that modern tiger sharks are older than previously thought and that several tiger shark species existed in past compared to the single species living today. The results of this study are published in the journal Paleobiology.

The fossil history of modern sharks reaches back to the Permian, about 295 million years ago. Complete fossil shark skeletons are very rare -- the skeleton, which consists almost entirely of cartilage, is only preserved under very special circumstances during the fossilization processes. Due to the lifelong continuous tooth replacement, most extinct sharks are therefore only known by their well-mineralized teeth, which, nonetheless, can provide deep insights into their evolutionary history.

The teeth of the modern tiger shark are unique: they have a broad, double-serrated cutting edge which even allows them to cut through sea turtle shells with ease. Tiger shark teeth are known in the fossil record since about 56 million years. Based on these fossil teeth, over 22 extinct tiger shark species have been described.

An international team of researchers led by Julia Türtscher from the University of Vienna has now examined the fossil history of the tiger shark and its extinct relatives. With the help of geometric morphometrics, the scientists were able to show that only 5 of the 22 known fossil tiger sharks actually represent valid species. Nevertheless, tiger sharks were more diverse in the past and only a single species survived until today.

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Ancient bony fish forces rethink of how sharks evolved

 Sharks' non-bony skeletons were thought to be the template before bony internal skeletons evolved, but a new fossil discovery suggests otherwise.

The discovery of a 410-million-year-old fish fossil with a bony skull suggests the lighter skeletons of sharks may have evolved from bony ancestors, rather than the other way around.

Sharks have skeletons made cartilage, which is around half the density of bone. Cartilaginous skeletons are known to evolve before bony ones, but it was thought that sharks split from other animals on the evolutionary tree before this happened; keeping their cartilaginous skeletons while other fish, and eventually us, went on to evolve bone.

Now, an international team led by Imperial College London, the Natural History Museum and researchers in Mongolia have discovered a fish fossil with a bony skull that is an ancient cousin of both sharks and animals with bony skeletons. This could suggest the ancestors of sharks first evolved bone and then lost it again, rather than keeping their initial cartilaginous state for more than 400 million years.

The team published their findings today in Nature Ecology & Evolution.

Lead researcher Dr Martin Brazeau, from the Department of Life Sciences at Imperial, said: "It was a very unexpected discovery. Conventional wisdom says that a bony inner skeleton was a unique innovation of the lineage that split from the ancestor of sharks more than 400 million years ago, but here is clear evidence of bony inner skeleton in a cousin of both sharks and, ultimately, us."

Most of the early fossils of fish have been uncovered in Europe, Australia and the USA, but in recent years new finds have been made in China and South America. The team decided to dig in Mongolia, where there are rocks of the right age that have not been searched before.

They uncovered the partial skull, including the brain case, of a 410-million-year-old fish. It is a new species, which they named Minjinia turgenensis, and belongs to a broad group of fish called 'placoderms', out of which sharks and all other 'jawed vertebrates' -- animals with backbones and mobile jaws -- evolved.

When we are developing as foetuses, humans and bony vertebrates have skeletons made of cartilage, like sharks, but a key stage in our development is when this is replaced by 'endochondral' bone -- the hard bone that makes up our skeleton after birth.

Previously, no placoderm had been found with endochondral bone, but the skull fragments of M. turgenensis were "wall-to-wall endochondral." While the team are cautious not to over-interpret from a single sample, they do have plenty of other material collected from Mongolia to sort through and perhaps find similar early bony fish.

And if further evidence supports an early evolution of endochondral bone, it could point to a more interesting history for the evolution of sharks.

Dr Brazeau said: "If sharks had bony skeletons and lost it, it could be an evolutionary adaptation. Sharks don't have swim bladders, which evolved later in bony fish, but a lighter skeleton would have helped them be more mobile in the water and swim at different depths.

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