How sharks and rays evolve

This 21 May 2020 video says about itself:

Sharks and Rays by Annie Crawley

Sharks & Rays takes you on a journey to discover the wonders of sharks and rays from around the world. Join underwater photographer, filmmaker and ocean explorer, Annie Crawley to learn all about these amazing creatures. You learn the biology with complex information in easy to understand language.

Exclusive footage will have you diving with schooling hammerhead sharks, observing manta rays feeding, nurse sharks entering a state of tonic immobility, plus you will experience the first Shark Sanctuary in the world while diving in the blue waters of Palau. Whale sharks, hammerheads, great white sharks, electric rays, manta rays, reef sharks, mako sharks, dozens of species of sharks and rays from around our world’s ocean are explored in this program.

From Flinders University in Australia:

Ecosystem diversity drives the origin of new shark and ray species

May 19, 2020

Summary: Biologists how different oceanographic conditions in the Gulf of California and the Baja California Peninsula influenced formation of new species of sharks and rays.

What drives the evolution of new species of sharks and rays? Traditionally, scientists thought it required species to be separated by geographic or spatial barriers, however, a new study of elasmobranchs (the group of sharks and rays) has challenged this expectation — and found evolution is happening faster than many think.

Flinders University evolutionary biologists Dr Jonathan Sandoval-Castillo and Professor Luciano Beheregaray tested how different oceanographic conditions in the Gulf of California and the Baja California Peninsula (Mexico) influenced the formation of new species of guitarfish (genus Pseudobatos).

The team discovered four types, or ‘young species’, of guitarfish that have similar external appearance but are genetically different.

Each type of guitarfish appears to have adapted to one of the four separate regions of the Gulf of California. This promotes environmental tolerances which result in those guitarfish having improved odds for survival and reproduction in the region where they were born.

“We have shown that these four guitarfish species evolved quite quickly from the same common ancestor,” says Dr Jonathan Sandoval-Castillo.

“The process where several new species originate from one ancestor in a relatively short period of time is called adaptive radiation, and this is the first report of such a process in sharks and rays. Our results help changing the false popular belief that sharks and rays do not evolve, or only evolve very slowly,” says Prof Luciano Beheregaray.

These findings also have important implications for the management of exploited elasmobranch species, such as guitarfish in the Gulf of California which represents an important fishery for Mexico.

If these young species adapt and evolve to their local habitat conditions, they cannot be replaced by migrants from other habitats.

“If such species are incorrectly managed as a single stock, it can result in the over-exploitation and possibly extinction of the entire species.”

Blacktip sharks fleeing from great hammerhead sharks

This 13 May 2020 video says about itself:

Can’t Touch This! Video Shows Blacktip Sharks Use Shallow Water to Flee Huge Predators

From Florida Atlantic University in the USA:

Can’t touch this! Video shows blacktip sharks use shallow water to flee huge predators

Aerial video provides first evidence of adult sharks using shallow water to escape the great hammerhead

May 13, 2020

Summary: Aerial drone footage provides the first evidence of adult blacktip sharks using shallow waters as a refuge from a huge predator — the great hammerhead. Before this study, documentation of adult sharks swimming in shallower waters to avoid predation did not exist. Unmanned aerial vehicles enable scientists to unobtrusively observe behaviors in the wild, providing insight into seldom-seen predator-prey interactions. When it comes to sharks, this ‘hammerhead’ time video proves you ‘can’t touch this.’

It’s “hammerhead” time according aerial drone footage of blacktip sharks fleeing to shallow waters when confronted by a huge predator along the coast of southeast Florida. Footage from the drone provides the first evidence of adult blacktip sharks (Carcharhinus limbatus) using shallow waters as a refuge from the great hammerhead shark (Sphyrna mokarran) — proving you “can’t touch this.”

Several juvenile shark species use shallow water nursery sites where the young can grow with a reduced risk of predation. However, prior to a study by Florida Atlantic University, no documentation was available to show that large adult sharks also swim in shallower waters to avoid predation.

The use of unmanned aerial vehicles (UAVs) enabled FAU scientists to unobtrusively observe and allow natural behaviors to be documented in the wild, providing insight into seldom-seen predator-prey interactions. Results of the study are published in the Journal of Fish Biology.

The blacktip shark is both an agile predator of teleost fishes, cephalopods and crustaceans and a prey for larger sharks, such as the great hammerhead, which can get as big as 18 feet long. Despite their large size, hammerheads are often found in relatively shallow waters that are likely an important area for their feeding. Their prey typically includes stingrays, bony fishes and other sharks, so it is no surprise that they have been spotted in and around the blacktip shark aggregations, which provide an abundance of possible prey.

On three separate occasions, a UAV recorded footage of a hammerhead shark approaching an aggregation of blacktip sharks in the nearshore waters of Palm Beach County. The average length of the blacktips captured in the area is under 6 feet, which the researchers used to calibrate the scale in the video footage to estimate the distance from shore for these interactions. Based on this estimate, all videos were recorded less than 150 feet offshore of the beach, in water no more than waist-deep.

In all three events, blacktip sharks used the shallow waters close to shore as a refuge from a great hammerhead. The hammerhead sharks in the videos were at least twice the size of the blacktip sharks making them approximately 12 feet long. The three separate videos were recorded during the day on Feb. 28, 2018, Feb. 28, 2019 and March 3, 2019.

“In two of the three videos, the hammerhead shark actively chased one or more blacktips toward the shore but was unsuccessful at capturing its prey,” said Stephen Kajiura, Ph.D., senior author, a professor of biological sciences and director of the Elasmobranch Laboratory in FAU’s Charles E. Schmidt College of Science. Kajiura co-authored the paper with his undergraduate student and lead author, Melanie D. Doan. “The chases ended with the hammerhead making a sharp turn away from its intended prey and the shore, back into deeper waters. The chasing events showed the hammerhead struggling as it experienced difficulty following the blacktips into the shallow waters.”

Hammerheads are known to possess an exceptionally tall first dorsal fin, longer than their pectoral fins. Their large dorsal fin is proposed to generate lift when swimming on their side, instead of facilitating propulsion and precise turning, as seen in every other observed shark species. The caudal fin thrusts and propels the shark forward, but both the dorsal fin and upper lobe of the caudal fin are seen breaching the surface in each of the videos in the study.

“When the dorsal and caudal fins of hammerhead breach the surface, they are neither generating lift, providing thrust, nor helping to facilitate turning as efficiently as when they are completely submerged,” said Kajiura. “The shallow water thus constrains the locomotion of the hammerhead, which provides the blacktip shark with a functional refuge because their smaller size allows them to continue to swim and maneuver effectively away from their larger predator.”

Some of the footage analyzed in this study was generously provided by a local citizen scientist and filmmaker, Joshua Jorgensen. The increasing popularity of UAVs will likely lead to additional fortuitous observations that can further inform the understanding of behaviors that are difficult to observe or have been previously undocumented.

“The predictable seasonal occurrence of large numbers of blacktip sharks in clear, shallow waters close to the beach in Palm Beach County, Florida, provides an excellent opportunity to employ unmanned aerial vehicles to quantitatively explore the collective behaviors and swimming kinematics of large sharks during natural predator-prey interactions,” said Kajiura.

Funding for this study was provided by the Colgan Foundation.

Young dinosaur age shark discovery

Ptychodus mortoni shark

From the University of Vienna in Austria:

Giant teenage shark from the dinosaur era

Fossil vertebrae give insights into growth and extinction of an enigmatic shark group

April 23, 2020

Summary: Scientists examined parts of a vertebral column, which was found in northern Spain in 1996, and assigned it to the extinct shark group Ptychodontidae. In contrast to teeth, shark vertebrae bear biological information, like body size, growth, and age and allowed the team surrounding Patrick L. Jambura to gain new insights into the biology of this mysterious shark group.

In 1996, palaeontologists found skeletal remains of a giant shark at the northern coast of Spain, near the city Santander. Here, the coast comprises meter high limestone walls that were deposited during the Cretaceous period, around 85 million years ago, when dinosaurs still roamed the world. Scientists from the University of Vienna examined this material now and were able to assign the remains to the extinct shark family, Ptychodontidae, a group that was very specious and successful in the Cretaceous but suddenly vanished mysteriously before the infamous end-Cretaceous extinction event.

Shark vertebrae are rare in the fossil record, but precious

Ptychodontid sharks are mainly known from their teeth, which are flattened and allowed them to crush hard-shelled prey, like bivalves or ammonites, similar to some of today’s ray species. However, the find of Spain consists only of parts of the vertebral column and placoid scales (teeth-like scales), which are much rarer than teeth in the fossil record.

In contrast to teeth, shark vertebrae bear important information about a species’ life history, such as size, growth and age, which are saved as growth rings inside the vertebra, like in the stem of trees. Statistical methods and the comparison with extant species, allowed the scientists to decode these data and reconstruct the ecology of this enigmatic shark group.

Ptychodontid sharks grew big and old

“Based on the model, we calculated a size of 4-7m and an age of 30 years for the examined shark. Astonishing about this data is the fact that this shark was not yet mature when it died despite its rather old age”, states Patrick L. Jambura, lead author of the study. Sharks follow an asymptotic growth curve, meaning that they grow constantly until maturation and after that, the growth curve flattens resulting from a reduced growth rate. “However, this shark doesn’t show any signs of flattenings or inflections in the growth profile, meaning that it was not mature, a teenager if you want. This suggests that these sharks even grew much larger (and older)!”

The study suggests that ptychodontid sharks grew very slow, matured very late, but also showed high longevity and reached enormous body sizes. “This might have been a main contributor to their success, but also, eventually, demise.”

Do modern sharks face a similar fate?

Many living sharks, like the whale shark or the great white shark, show very similar life-history traits, a combination of low recruitment and late maturation, which makes them vulnerable to anthropogenic threats, like overfishing and pollution.

“It might be the case that similar to today’s sharks, ptychodontid sharks faced changes in their environment, to which they could not adapt quick enough and, ultimately, led to their demise before even dinosaurs went extinct. However, unlike in the Cretaceous period, it is up to us now, to prevent this from happening to modern sharks again and to save the last survivors of this ancient and charismatic group of fishes!”

Whale sharks and nuclear bombs

This 2019 video says about itself:

Whale Sharks: Meet The Gentle Giants Of The Sea! | The Blue Realm

Scientists are racing against time to save the whale shark. Utilizing space-age technology from NASA and the Hubble Telescope, researchers are able to identify, catalogue and track individual animals.

From the Australian Institute of Marine Science:

Cold War nuclear bomb tests reveal true age of whale sharks

The radioactive legacy of the arms race solves a mystery about the world’s largest fish

April 6, 2020

Atomic bomb tests conducted during the Cold War have helped scientists for the first time correctly determine the age of whale sharks.

The discovery, published in the journal Frontiers in Marine Science, will help ensure the survival of the species — the largest fish in the world — which is classified as endangered.

Measuring the age of whale sharks (Rhincodon typus) has been difficult because, like all sharks and rays, they lack bony structures called otoliths that are used to assess the age of other fish.

Whale shark vertebrae feature distinct bands — a little like the rings of a tree trunk — and it was known that these increased in number as the animal grew older. However, some studies suggested that a new ring was formed every year, while others concluded that it happened every six months.

To resolve the question, researchers led by researchers led by Joyce Ong from Rutgers University in New Jersey, USA, Steven Campana from the University of Iceland, and Mark Meekan from the Australian Institute of Marine Science in Perth, Western Australia, turned to the radioactive legacy of the Cold War’s nuclear arms race.

During the 1950s and 1960s, the USA, Soviet Union, Great Britain, France and China conducted tests of nuclear weapons. Many of these were explosions detonated several kilometres in the air.

One powerful result of the blasts was the temporary atmospheric doubling of an isotope called carbon-14.

Carbon-14 is a naturally occurring radioactive element that is often used by archaeologists and historians to date ancient bones and artefacts. Its rate of decay is constant and easily measured, making it ideal for providing age estimates for anything over 300 years old.

However, it is also a by-product of nuclear explosions. Fallout from the Cold War tests saturated first the air, and then the oceans. The isotope gradually moved through food webs into every living thing on the planet, producing an elevated carbon-14 label, or signature, which still persists.

This additional radioisotope also decays at a steady rate — meaning that the amount contained in bone formed at one point in time will be slightly greater than that contained in otherwise identical bone formed more recently.

Using bomb radiocarbon data prepared by Steven Campana, Ong, Meekan, and colleagues set about testing the carbon-14 levels in the growth rings of two long-dead whale sharks stored in Pakistan and Taiwan. Measuring the radioisotope levels in successive growth rings allowed a clear determination of how often they were created — and thus the age of the animal.

“We found that one growth ring was definitely deposited every year,” Dr Meekan said.

“This is very important, because if you over- or under-estimate growth rates you will inevitably end up with a management strategy that doesn’t work, and you’ll see the population crash.”

One of the specimens was conclusively established as 50 years old at death — the first time such an age has been unambiguously verified.

“Earlier modelling studies have suggested that the largest whale sharks may live as long as 100 years,” Dr Meekan said.

“However, although our understanding of the movements, behaviour, connectivity and distribution of whale sharks have improved dramatically over the last 10 years, basic life history traits such as age, longevity and mortality remain largely unknown.

“Our study shows that adult sharks can indeed attain great age and that long lifespans are probably a feature of the species. Now we have another piece of the jigsaw added.”

Whale sharks are today protected across their global range and are regarded as a high-value species for eco-tourism. AIMS is the world’s leading whale shark research body, and the animal is the marine emblem of Dr Meekan’s home state, Western Australia.

Drs Ong, Meekan, and Campana were aided by Dr Hua Hsun Hsu from the King Fahd University of Petroleum and Minerals in Saudi Arabia, and Dr Paul Fanning from the Pakistan node of the UN Food and Agricultural Organisation.

New sawshark species discoveries

This 2018 video is called The Life of a Sawfish.

Sawfish, which are rays, should not be confused with sawsharks.

This 2015 video is called Japanese Sawshark.

From Newcastle University in England:

New species of sawsharks found in West Indian Ocean

March 18, 2020

Summary: Two new species of sawsharks discovered in the West Indian Ocean reinforces how much we still don’t know about life in the ocean and the impact climate change is having on it.

Not one, but TWO new species of the rarely seen six-gilled sawsharks have been found in the West Indian Ocean by an international team of marine scientists.

The newly discovered Pliotrema kajae and Pliotrema annae — affectionately known as Kaja’s and Anna’s six-gill sawsharks — were discovered during research investigating small-scale fisheries operating off the coasts of Madagascar and Zanzibar.

Publishing their findings today in the journal PLOS ONE, the study team say the discovery of two new sharks highlights how little we still know about life in the ocean and the impact we are having on it.

Lead author Dr Simon Weigmann, based at the Elasmobranch Research Laboratory in Hamburg, explained:

“The six-gill sawsharks are really quite extraordinary as most sawsharks have five gill slits per side.

“So it was really exciting to find a new six-gill sawshark species and to find two new species — well that was simply astonishing!

“Knowledge of sawsharks in the western Indian Ocean is generelly still scarce. But considering their known depth distributions, both new species are likely affected by fishing operations.

“This assumption, combined with the limited range and apparent rarity of both new species, raises concerns that they are vulnerable to overfishing and might be in continuing decline.

“This could be particularly alarming for Anna’s six-gill sawshark due to its very small known range, rarity and occurrence in shallow waters as the species is only known from depths of 20 to 35 m.”

Two rostra of P.kajae were collected by Dr Ruth Leeney based at the Natural History Museum in London and many further specimens of this new species were found in different museum collections. The two specimens of P.annae were collected by PhD student Ellen Barrowclift, Dr Andrew Temple and Dr Per Berggren from Newcastle University, UK, and Dr Narriman Jiddawi from the Institute of Fisheries Research, Zanzibar.

Dr Temple, a co-author on the paper, said:

“Last year our team highlighted the massive underreporting of sharks and rays caught in the South West Indian Ocean and the urgent need to expand efforts globally to assess the impact of these fisheries on vulnerable species.

“The discovery re-enforces both how important the western Indian Ocean is in terms of shark and ray biodiversity, but also how much we still don’t know.”

Dr Berggren, a co-author on the paper and leader of Newcastle’s Marine MEGAfauna lab, adds:

“This project is also testament to the value of scientists working with local communities. Without the fishers´ help we would not have discovered these animals. Their knowledge of their environment is unparalleled and it is our mission to help them preserve the marine animals and ecosystems they rely on to survive.”

As its name suggests, the sawshark is a type of shark best known for its saw-like snout. Found mainly in the temperate waters of all three major oceans (with the centre of distribution in the western Pacific Ocean), the number of sawsharks has declined in the past couple of decades due to commercial fishing.

Sawsharks can reach up to about 1.5 metres in length and have a long snout edged with sharp teeth which alternate in size (smaller teeth are inserted between larger teeth).

They also has a distinctive pair of barbels in the middle of the snout — whisker-like sensory organs around the shark’s mouth which help the shark detect its prey.

Even though the sawshark and sawfish share similarities in appearance, they differ in several aspects. Sawfish are larger, they don’t have barbels, and their gills are located on the bottom side of the body (like typical for rays).

Sawsharks are carnivores, living on a diet of fish, crustaceans and squid, and use their serrated snout to kill their prey. Fast movement of the snout from side to side cuts the prey into fine pieces that can be swallowed easily.

Both new species differ from the only previously known six-gill species, Pliotrema warreni, in the position of their barbels: in P. kajae and P. annae, these are situated approximately halfway from the tip of the saw — the rostral tip — to the mouth, compared to P. warreni, where they are about two-thirds of the way down, much closer to the mouth.

A special feature of P. annae is the generally shorter rostrum as compared to P. kajae and P. warreni.

Little cookiecutter sharks attack United States navy

This 6 March 2029 video from the USA says about itself:

How a Little Shark Destroyed the US Navy

Hey, guys, hope you enjoyed this short video between projects! I had a lot of fun learning about the cookiecutter shark and its related species as well as our relationship with the ocean itself. My apologies for the crappy microphone this episode (I was travelling).

Sharks and whales, video

This 3 March 2020 video says about itself:

A Deep Dive Into the Lives of Sharks and Whales

Join us for a deep dive into the world of sharks and orcas. In this reel, we meet people who study, swim with and photograph these fascinating mammals, from the warm waters of Bimini to the frigid Arctic Ocean.

How suckerfish hitchhike with sharks

This 2016 video says about itself:

Sharks and many other large ocean animals have sucker-equipped fish called remoras sticking to them. What are the remoras doing? Do they harm the shark? Jonathan goes on a mission to investigate remoras and their role in the food web. He even sticks one on himself.

From ScienceDaily:

Vertical fibers in the suckerfish’s suction cup-like fin help it hitchhike

February 26, 2020

As the hitchhikers of the marine world, the remora fish is well known for getting free rides by gripping onto hosts with its suction disc, a highly modified dorsal fin on its head. Now, work investigating the suction disc — appearing February 26 in the journal Matter — reveals that one of the secrets to the fish’s strong grip lies within the unique architecture of the lip of the disc.

“The remora fish‘s body shape and poor swimming ability don’t give him an edge in nature,” says senior co-author Li Wen of Beihang University, describing the flat-headed, eel-like fish. “The fish had to evolve its fin into a suction cup for hitchhiking for two reasons: food and mating.”

The suction disc of the remora — also known as the suckerfish or sharksucker — is so powerful that the fish can even stay attached to leaping dolphins. To understand the underlying mechanism, the researchers looked into the tissue on the soft lip of the suction disc. Between the surface and under-skin layer, they discovered a unique structure: vertically oriented collagen fibers. The fibrous structure provides elasticity for maximizing contact with substrates and decreases the deformation of the lip to maintain its adhesive force. This is the first paper to reveal the detailed morphology structure of the lip disc tissue in remora fish.

“Our research about remoras started with our co-senior author Li Wen’s study on sharks’ skin structure,” said corresponding author Juan Guan of Beihang University. “We were fascinated by the fact that remoras’ suction disc can adhere to surfaces as rough as sharkskin. Sharks swim very fast, yet remoras can hold on to the sharks’ skin very tightly.”

Inspired by the fish, researchers engineered a biomimetic disc infused with vertical nylon fibers with electrostatic flocking, a technique that utilizes an electric charge to align fibers. Compared to pure silicon discs, the biomimetic discs demonstrate an adhesion enhancement of 62.5% and show 3.4 times increment in attachment time. Moreover, the fiber-reinforced biomimetic sucker can hang onto objects that are heavy, irregular, rough, and even under aquatic conditions.

“There are some limitations in controlling the fiber density,” says Guan. “Although nylon and collagen are similar to some extent, we can’t fully mimic their morphological and chemical composition. But we proved a simple concept: by adding vertical fibers to your sucker, you can improve the sucker’s functionality significantly. We’re doing work that can be applied in real life.”

The next step for the team is to improve the current biomimetic sucker by studying and mimicking the structure on the surface skin and under-skin layer. Other improvements include introducing environmentally friendly and biodegradable materials such as silk. The development of vertical fibers could also be applied in soft robotics to achieve intricate movements through controlling deformation.

“There’s a lot of potential in future applications,” says Wen. “I’m a mechanical engineer; I make robots. If we can make a robot with a suction disc as strong as the remora’s, it could travel the world attached to whales and sharks. The mobile biomimetic device will be able to gather meaningful bio and environmental data. I hope the suction disc can be applied to protecting the marine environment and contribute to the marine bio-monitoring system in the future.”

This work was supported by the Fundamental Research Funds for the Central Universities, National Natural Science Foundation of China support projects, and National Key R&D Program of China.

Good Mexican great white shark news

This 13 February 2020 video says about itself:

Great white sharks are making a great big comeback in Mexico

Sharks play a key role in keeping oceans healthy, but their numbers plunged by over 70% in some places around the world. The great white is still considered vulnerable, but is making a comeback thanks to stronger environmental protections. Jonathan Vigliotti gets up close and personal with them in one protected area where their population is booming for our series Eye on Earth.