Sea angels, sharks or rays?


This April 2020 video from California in the USA is called Angel Shark Quest | JONATHAN BIRD’S BLUE WORLD.

From the University of Vienna in Austria:

Between shark and ray: The evolutionary advantage of the sea angels

Threatened with extinction despite perfect adaptation

August 4, 2020

Summary: Angel sharks are sharks, but with their peculiarly flat body they rather resemble rays. An international research team has now investigated the origin of this body shape. The results illustrate how these sharks evolved into highly specialized, exclusively bottom-dwelling ambush predators and thus also contribute to a better understanding of their threat from environmental changes

The general picture of a shark is that of a fast and large ocean predator. Some species, however, question this image — for example angel sharks. They have adapted to a life on the bottom of the oceans, where they lie in wait for their prey. In order to be able to hide on or in the sediment, the body of angel sharks became flattened in the course of their evolution, making them very similar to rays, which are closely related to sharks.

Flattened body as indication for a successful lifestyle

The oldest known complete fossils of angel sharks are about 160 million years old and demonstrate that the flattened body was established early in their evolution. This also indicates that these extinct angel sharks already had a similar lifestyle as their extant relatives — and that this lifestyle obviously was very successful.

Angel sharks are found all over the world today, ranging from temperate to tropical seas, but most of these species are threatened. In order to understand the patterns and processes that led to their present low diversity and the possible consequences of their particular anatomy, the team has studied the body shapes of angel sharks since their origins using modern methods.

Today’s species are very similar

For this purpose, the skulls of extinct species from the late Jurassic period (about 160 million years ago) and of present-day species were quantitatively analysed using X-ray and CT images and prepared skulls employing geometric-morphometric approaches. In doing so, the evolution of body shapes could be explained comparatively, independent of body size.

The results show that early angel sharks were different in their external shape, whereas modern species show a comparably lower variation in shape. “Many of the living species are difficult to identify on the basis of their skeletal anatomy and shape, which could be problematic for species recognition,” explains Faviel A. López-Romero.

Angel sharks are well adapted, but react slowly to environmental changes

It has been shown that in living species the individual parts of the skull skeleton are more closely integrated than in their extinct relatives. This led to a reduced variability in appearance during the evolution of angel sharks. “The effect of integrating different parts of the skull into individual, highly interdependent modules can lead to a limited ability to evolve in different forms, but at the same time increases the ability to successfully adapt to specific environmental conditions,” explains Jürgen Kriwet.

In the case of the angel sharks, increasing geographical isolation resulted in the development of different species with very similar adaptations. “But modular integration also means that such animals are no longer able to react quickly to environmental changes, which increases their risk of extinction,” concludes Jürgen Kriwet.

Bad sharks news


This July 2019 video says about itself:

Sharks 101 | National Geographic

Sharks can rouse fear and awe like no other creature in the sea. Find out about the world’s biggest and fastest sharks, how sharks reproduce, and how some species are at risk of extinction.

From the University of Exeter in Engeland, 22 July 2020:

Microplastics have been found in the guts of sharks that live near the seabed off the UK coast.

University of Exeter scientists studied four species of demersal (seabed-dwelling) shark.

Of the 46 sharks examined, 67% contained microplastics and other human-made fibres.

From James Cook University in Australia, 22 July 2020:

A massive global study of the world’s reefs has found sharks are ‘functionally extinct’ on nearly one in five of the reefs surveyed.

Professor Colin Simpfendorfer from James Cook University in Australia was one of the scientists who took part in the study, published today in Nature by the Global FinPrint organisation. He said of the 371 reefs surveyed in 58 countries, sharks were rarely seen on close to 20 percent of those reefs.

How tiger sharks travel, new research


This 2018 video is called Tiger shark face-off.

From Florida Atlantic University in the USA:

Study first to show tiger sharks’ travels and desired hangouts in the Gulf of Mexico

Using satellite telemetry, FAU Harbor Branch scientist and team document core habitat use

July 15, 2020

Summary: From 2010 to 2018, scientists tagged 56 tiger sharks of varying life stages to track their movements via satellite. Movement patterns varied by life stage, sex, and season. Some of their core habitats overlapped with locations designated by NOAA as Habitat Areas of Particular Concern and also were found near 2,504 oil and gas platforms. Findings may help inform studies into potential climate change, oil spills, and other environmental impacts on tiger shark movement in the Gulf of Mexico.

Like other highly migratory sharks, tiger sharks (Galeocerdo cuvier) often traverse regional, national and international boundaries where they encounter various environmental and human-made stressors. Their range and habitat use in the Gulf of Mexico, a complex marine environment significantly impacted by the Deepwater Horizon Oil Spill in 2010, has been understudied and remains unknown.

Using sophisticated satellite telemetry, a study is the first to provide unique insights into how tiger sharks move and use habitats in the Gulf of Mexico across life-stages. Data from the study, just published in PLOS ONE, provide an important baseline for comparison against, and/or predicting their vulnerability to future environmental change such as climate variability or oil spills.

For the study, Matt Ajemian, Ph.D., lead author and an assistant research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute, and a team of scientists examined size and sex-related movement and distribution patterns of tiger sharks in the Gulf of Mexico. They fitted 56 tiger sharks with Smart Position and temperature transmitting tags between 2010 — following the Deepwater Horizon Oil Spill — and 2018 — spanning shelf waters from south Texas to south Florida and examined seasonal and spatial distribution patterns across the Gulf of Mexico. The tags transmitted whenever the fin-mounted tags broke the sea surface, with orbiting satellites estimating shark positions based on these transmissions. Ajemian also analyzed overlap of core habitats among individuals relative to large benthic features including oil and gas platforms, natural banks, and bathymetric breaks.

“While all life stages of tiger sharks are known to occur in the Gulf of Mexico, detailed habitat use has never been quantified,” said Ajemian. “This is rather striking as this marine system faces numerous human-madeResults showed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf stressors, complex tri-national management, and indications of size reductions in recreational landings for large sharks.”

Results showed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Prior studies into tiger shark horizontal movements in the western North Atlantic Ocean have been restricted primarily to males or females separately, in disparate locations. By simultaneously tracking many males and females of varying life stages within the same region, the researchers observed sex and size-specific differences in distribution and movement rates, as well as associations with large-scale habitat features. For example, researchers found evidence of tiger shark core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern during cooler months, particularly by females. These are specifically bottom features of the Gulf that rise up from the edges of the continental shelf, and include places like the Flower Garden Banks National Marine Sanctuary. Additionally, shark core regions intersected with 2,504 oil and gas platforms, where previous researchers have observed them along the bottom.

Results showed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Prior studies into tiger shark horizontal movements in the western North Atlantic Ocean have been restricted primarily to males or females separately, in disparate locations. By simultaneously tracking many males and females of varying life stages within the same region, the researchers observed sex and size-specific differences in distribution and movement rates, as well as associations with large-scale habitat features. For example, researchers found evidence of tiger shark core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern during cooler months, particularly by females. These are specifically bottom features of the Gulf that rise up from the edges of the continental shelf, and include places like the Flower Garden Banks National Marine Sanctuary. Additionally, shark core regions intersected with 2,504 oil and gas platforms, where previous researchers have observed them along the bottom.

The scientists note that future research may benefit from combining alternative tracking tools, such as acoustic telemetry and genetic approaches, which can facilitate long-term assessment of tiger shark movement dynamics and help identify the role of the core habitats identified in this study.

“This research is just a first glimpse into how these iconic predators use the Gulf of Mexico’s large marine ecosystem,” said Ajemian.

Nine walking shark species discovered


This 20 June 2020 video says about itself:

Scientists have discovered 9 species of ‘walking’ sharks.

In US news and current events today, researchers have confirmed that walking sharks branched from their nearest ancestor 9 million years ago, making them the most recently evolved type of shark. These sharks, who use their fins to ‘walk’ on the ocean floor, have been found off the coasts of Australia, Indonesia & New Guinea. Scientists have discovered a total of 9 species of walking sharks over the past 2 decades.

Read more here.

New shark species discovered off Japan


The Shirai’s spurdog (Squalus shiraii): lateral (A-C) and ventral (D, E) views. Scale bars – 50 mm. Image credit: Viana & Carvalho, doi: 10.3897/zse.96.51962

From ScienceDaily:

A new character for Pokémon? Novel endemic dogfish shark species discovered from Japan

June 11, 2020

Summary: A new endemic deep-water dogfish shark: Squalus shiraii, was discovered in the tropical waters of Southern Japan by an international team of scientists. The finding brings the amount of spurdog shark species inhabiting Japanese waters to six.

Newly discovered creatures can often be as impressive and exciting as the ones from the Japanese movies and shows. Many of those fictional characters, including inhabitants of the famous Pokémon universe, might have their analogues among the real animals native to Japan. Maybe, a new species of the dogfish shark published in the open-access journal Zoosystematics and Evolution is also “a real Pokémon” to be?

A new deep-water dogfish shark: Squalus shiraii, was discovered in the tropical waters of Southern Japan by an international team of scientists, led by Dr. Sarah Viana from South African Institute for Aquatic Biodiversity.

The new shark has the body length of 59-77 cm and some unique characteristics such as tall first dorsal fin and caudal fin with broad white margins. Currently, the species is known exclusively as a Japanese endemic, occurring in the tropical shallow waters of Southern Japan in the North-western Pacific.

Spurdogs are commercially important for the world fish trade taxa. They are caught for a range of purposes: consumption of meat, fins and liver oil. Despite their high occurrence, the accurate identification data of species is scarce, population threats and trends remain unknown.

Japan currently represents one of the world’s leading shark fish trade countries, though, during the last decades the amount of shark catches is decreasing and over 78 elasmobranch species traded in Japanese shark fin markets are now evaluated as threatened.

The new species Squalus shiraii previously used to be massively misidentified with shortspine spurdog, due to the resembling shape of body, fins and snout length. However, there are some differences, defining the specificity of the new species.

“Squalus shiraii has body brown in colour, postventral and preventral caudal margins whitish, dorsal and ventral caudal tips broadly white and black upper caudal blotch evident in adults. S. mitsukurii has body conspicuously black to dark grey and caudal fins black throughout with post-ventral caudal margin fairly whitish and black upper caudal blotch not evident in adults,” shares lead author Dr. Viana.

Scientists propose the name for the newly described species as Shirai’s spurdog in honor to Dr. Shigeru Shirai, the former Japanese expert of the group.

Swimming with whale sharks


This 19 May 2020 BBC video says about itself:

Swim With The Biggest Fish In The Ocean | VR 360 | Seven Worlds, One Planet

Whale sharks share the fishermen’s catch in the seas of Indonesia. These gentle giants were once hunted and killed, but here their numbers are on the rise thanks to this special relationship. Stay in and explore their underwater world.

First fossil great white shark nursery discovered


This September 2014 video says about itself:

Scientists discover a great white shark pupping ground in the Sea of Cortez.

From the University of Vienna in Austria:

First fossil nursery of the great white shark discovered

Paleo-kindergarten ensured evolutionary success millions of years ago

May 22, 2020

Summary: An international research team discovered the first fossil nursery area of the great white shark, Carcharodon carcharias in Chile. This discovery provides a better understanding of the evolutionary success of the largest top predator in today’s oceans in the past and could contribute to the protection of these endangered animals.

The great white shark is one of the most charismatic, but also one of the most infamous sharks. Despite its importance as top predator in marine ecosystems, it is considered threatened with extinction; its very slow growth and late reproduction with only few offspring are — in addition to anthropogenic reasons — responsible for this.

Young white sharks are born in designated breeding areas, where they are protected from other predators until they are large enough not to fear competitors any more. Such nurseries are essential for maintaining stable and sustainable breeding population sizes, have a direct influence on the spatial distribution of populations and ensure the survival and evolutionary success of species. Researchers have therefore intensified the search for such nurseries in recent years in order to mitigate current population declines of sharks by suitable protection measures. “Our knowledge about current breeding grounds of the great white shark is still very limited, however, and palaeo-nurseries are completely unknown,” explains Jaime Villafaña from the University of Vienna.

He and his colleagues analysed statistically 5 to 2 million-year-old fossil teeth of this fascinating shark, which were found at several sites along the Pacific coast of Chile and Peru, to reconstruct body size distribution patterns of great white shark in the past. The results show that body sizes varied considerably along the South American paleo-Pacific coast. One of these localities in northern Chile, Coquimbo, revealed the highest percentage of young sharks, the lowest percentage of “teenagers.” Sexually mature animals were completely absent.

This first undoubted paleo-nursery of the Great White Shark is of enormous importance. It comes from a time when the climate was much warmer than today, so that this time can be considered analogous to the expected global warming trends in the future. “If we understand the past, it will enable us to take appropriate protective measures today to ensure the survival of this top predator, which is of utmost importance for ecosystems,” explains palaeobiologist Jürgen Kriwet: “Our results indicate that rising sea surface temperatures will change the distribution of fish in temperate zones and shift these important breeding grounds in the future.”

This would have a direct impact on population dynamics of the great white shark and would also affect its evolutionary success in the future. “Studies of past and present nursery grounds and their response to temperature and paleo-oceanographic changes are essential to protect such ecological key species,” concluded Jürgen Kriwet.

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!”