Top 10 smallest sharks

This 14 August 2018 video says about itself:

Meet the top 10 smallest sharks in the world.

You already know the biggest sharks like the megalodon or the great white shark, but it’s time you saw these predators in their smaller version. Here is the list of the tiniest sharks that exist in the world.

Dwarf lantern shark
Cylindrical lanternshark
Pale Catshark
Smalleye pygmy shark
Panama Ghost Catshark
Pygmy ribbontail catshark
Green lanternshark
Broadnose Catshark
Pygmy shark
Spined pygmy shark


Entangled whale shark saved

This video says about itself:

Watch A Free-Diver Rescue This Entangled Whale Shark | National Geographic

20 August 2018

A Hawaiian family spotted this whale shark while free-diving off the coast of Lanai. First, they were excited about the rare sighting of the 20-foot-long endangered shark. But then, they noticed a heavy rope tightly wrapped around its neck. Biologists Kapua Kawelo and Joby Rohrer decided to help the animal, while their son, 17-year-old Kanehoalani, filmed the rescue.

Megalodon sharks, film fiction and reality

This video is called The Meg, Official Trailer #1 (2018). Jason Statham, Ruby Rose: Megalodon Shark Movie HD.

By Carolyn Gramling, 12:41pm, August 10, 2018:

What ‘The Meg’ gets wrong — and right — about megalodon sharks

A paleobiologist helps Science News separate fact from fiction in the film

OK, so what if a giant prehistoric shark, thought to be extinct for about 2.5 million years, is actually still lurking in the depths of the ocean? That’s the premise of the new flick The Meg, which opens August 10 and pits massive Carcharocles megalodon against a grizzled and fearless deep-sea rescue diver, played by Jason Statham, and a handful of resourceful scientists.

The protagonists discover the sharks in a deep oceanic trench about 300 kilometers off the coast of China — a trench, the film suggests, that extends down more than 11,000 meters below the ocean surface. (That depth makes it even deeper than the Mariana Trench’s Challenger Deep, the actual deepest known point in the ocean). Hydrothermal vents down in the trench supposedly keep those dark waters warm enough to support an ecosystem teeming with life. And — spoiler alert!—   of course, the scientists’ investigation inadvertently helps megalodons escape from the depths. The giant living fossils head to the surface, where they terrorize shark fishermen and beachgoers a la Jaws.

But could a population of megalodons actually have survived down there? To explore what is and isn’t possible and what we still don’t know about sharks, Science News went to the movies with paleobiologist Meghan Balk of the Smithsonian’s National Museum of Natural History in Washington, D.C., who studies the ancient predators.

Did megalodons ever actually get as big as they are in the movie? Extremely unlikely

The megalodon sharks of The Meg reach sizes of about 20 to 25 meters long, the film says — massive although just a tad smaller than the longest known blue whales. But estimates based on the size of fossil teeth suggest that even the largest known C. megalodon was much smaller, at up to 18 meters — “and that was the absolute largest”, Balk says. On average, C. megalodon tended to be around 10 meters long, she says, which still made them much bigger than the average great white shark, at around 5 to 6 meters long.

Would a megalodon otherwise look like the film version? Yes and no

The movie’s sharks aren’t entirely inaccurate representations, Balk says. These megalodons correctly have six gills — between five and seven is accurate for sharks in general, she says. And the shape of the dorsal fin is, appropriately, modeled after the great white shark, the closest modern relative to the ancient sharks. Also, a male meg in the film even has “claspers”, appendages under the abdomen used to hold a female during mating. “When I looked at it, I was like, oh, they did a pretty good job. They didn’t just create a random shark”, Balk says.

On the other hand, it’s actually a bit odd that the movie’s megalodons wouldn’t have evolved some significant anatomical differences from their prehistoric brethren, Balk says. “Like the eye getting bigger” to see better or becoming blind after a few million or so years living in the darkness of the deep sea, she says. Or you might even expect dwarfism, in which populations restricted by geographic isolation, such as being stuck within a trench, shrink in size.

Would such huge sharks have had enough to eat down there? Extremely unlikely

In general, “there’s just not enough energy in the deep sea” to sustain giant sharks, Balk says. Life does bloom at hydrothermal vents, although the deepest known hydrothermal vents are only about 5,000 meters deep. But even if there were vents in the deepest trenches, it’s not clear there would be enough big species living down there to sustain not just one, but a whole population of massive sharks. In the film, the vent field is populated with many smaller species known to cluster around hydrothermal vents, including shrimps, snails and tube worms. Viewers also see one giant squid, but there would have had to be a whole lot more food of that size. C. megalodon — like modern great whites — ate many different things, from orcas to squid. And the humongous megalodon sharks in the movie “would have eaten a lot of squid”, Balk says, laughing.

Could sharks live at such depths? Unlikely

How deep sharks can live in the ocean is actually still a big unknown (SN Online: 5/7/18). “Quantifying the depth that sharks go to is a big endeavor right now”, Balk says. Few sharks are known to inhabit the abyssal regions of the ocean below about 4,000 meters — let alone the depths of oceanic trenches lying below 6,000 meters. Aside from the scarcity of food, temperature is another limitation to deep-sea living.

Sharks that do inhabit deeper parts of the ocean, such as goblin sharks and the Greenland shark (SN 9/17/16, p. 13), tend to have low metabolic rates. That means they move much more slowly than the energetic predators of the movie, Balk says. C. megalodon, although it lived around the globe, tended to prefer warmer, shallower waters and used coastal regions as nursing grounds.

So, could megalodons have survived to modern times without humans knowing about it? Extremely unlikely

Sharks shed a lot of teeth throughout their lives, and those teeth are the main fossil evidence of the life and times of prehistoric sharks (SN Online: 8/2/18). Fossilized C. megalodon teeth found in sediments around the world suggest that the creatures lived between about 14 million and 2.6 million years ago — or perhaps up until 1.5 million years ago at the latest, Balk says. It’s not clear why they went extinct. But there are a handful of hypotheses: competition for food with other creatures like orcas; ocean circulation changes about 3 million years ago when the Isthmus of Panama formed (SN: 9/17/16, p. 12); nearshore nursery sites vanished; or possibly a loss of prey sources stemming from a marine mammal extinction about 2.6 million years ago.

Bottom line: The sheer abundance of shed teeth — as many as 20,000 per shark in its lifetime  — is one of the strongest arguments against megalodon surviving into modern times, Balk says. “That’s one of the reasons why we know megalodon’s definitely extinct. We would have found a tooth.”

“The Meg”, Warner Bros.’ big-budget shark flick, took $44.5 million at the domestic box office on its opening weekend — jumping into the No. 1 spot.

Whale shark travels, new research

This video from Tanzania says about itself:

Investigating the Mysterious Whale Sharks of Mafia Island | National Geographic

24 January 2017

The whale sharks of Mafia Island are unusual because they don’t migrate—and researchers want to know why.

From the University of Southampton in England:

‘Biological passport’ to monitor Earth’s largest fish

Whale sharks, the world’s largest fish, roam less than previously thought

August 9, 2018

Summary: Whale sharks, the world’s largest fish, roam less than previously thought. This new study used stable isotope analysis to demonstrate that whale sharks feeding at three disparate sites in the Western Indian Ocean and Arabian Gulf rarely swim more than a few hundred kilometers north or south from these areas according to researchers.

Whale sharks, the world’s largest fish, roam less than previously thought. Local and regional actions are vital for the conservation of this globally endangered species moving forward, according to a new study by researchers from the Marine Megafauna Foundation, University of Southampton, and Sharkwatch Arabia. Their findings are published today in the journal Marine Ecology Progress Series.

Previously, genetic research indicated that whale sharks mixed within distinct populations in the Indo-Pacific and Atlantic Ocean, respectively. This new study used stable isotope analysis, a biochemical technique, to demonstrate that whale sharks feeding at three disparate sites in the Western Indian Ocean (Mozambique and Tanzania) and the Arabian Gulf (Qatar) rarely swim more than a few hundred kilometres north or south from these areas.

“Whale sharks are amazing swimmers, often moving over 10000 km each year, and they can dive to around 2000 meters in depth. Biochemical studies tell us more about where they go and what they do when they’re out of our sight”, said Dr Clare Prebble, who led the research as part of her PhD project at the University of Southampton.

The researchers used isotopes of nitrogen and carbon that have similar chemical properties, but vary in their atomic mass. Ratios between the heavier and lighter isotopes of these elements vary naturally across different habitats in the marine environment. For example, more of the heavier isotopes are found in near-shore environments than offshore. These ratios stay consistent as they are passed up through the food web, from tiny marine plants to top predators, and therefore provide a record of the animal’s feeding and movement behaviours. Stable isotope analysis thereby provides a ‘biological passport’ for whale sharks.

Electronic tags are commonly used with marine animals to record their movements and diving behaviours. However, the challenge of keeping them attached to a large shark, while minimizing disturbance, has meant that only short-term deployments (weeks to months) have been possible. This study used tiny samples of skin tissue from wild, free-swimming whale sharks. These small pieces of skin, collected over 2-3 years at each location, were sufficient to reconstruct the sharks’ movements and feeding preferences over the weeks and months prior to sampling.

Values of both carbon and nitrogen stable isotopes differentiated at each site. To complement the biochemical analysis, the researchers also took photographs of the natural markings on each whale shark to identify and track individuals over a 10-year timeframe. Every whale shark has a unique spot pattern, similar to a human fingerprint. The team recorded 4197 encounters with 1240 individual whale sharks within these three countries.

Only two sharks moved between sites, both swimming around 2000 km north from Mozambique to Tanzania. Taken together, these findings indicate that there are limited movements between these major aggregation sites over months to years. These results have implications for the conservation of this endangered species.

“The best data available suggests that more than half of the world’s whale sharks have been killed since the 1980s. Although the Western Indian Ocean remains a global hotspot for the species, even the largest feeding areas only host a few hundred sharks. Our results show that we need to treat each site separately, and ensure good conservation management is in place, as the sharks may not re-populate if they’re impacted by people’s activities”, Prebble added.

The study stresses the need to protect these filter-feeding sharks at the areas where they come together in numbers, particularly where human pressures are also present. Whale sharks are an incidental catch in coastal gillnets, which are frequently used in Mozambique and Tanzania. The Arabian Gulf is a huge oil shipping area where vessel strikes pose a major threat to the sharks when they are feeding near the surface.

“Whale sharks are fully capable of swimming across oceans, but it seems like the juveniles, at least, are choosing not to”, commented Dr Simon Pierce, Principal Scientist at the Marine Megafauna Foundation and a co-author on this study. “They like coming back to the same sites each year to take advantage of predictable feeding opportunities. Looking on the bright side, that emphasises that local protection can have a major benefit for the recovery of this endangered species. The rewards can also be felt locally, with whale shark tourism now worth over $100 million each year around the world.”

Earlier this year, colleagues reported that whale sharks regularly visit Madagascar to feed, which has led to a growing ecotourism industry between the months of September and December. To date, none of the sharks identified in Madagascar have been seen outside that country, further reinforcing the results from this new study.

Dr Clive Trueman from the University of Southampton concluded: “Interestingly, most sharks found at these feeding sites are juvenile males of less than nine meters. To truly assess how populations are globally structured and distributed, we need to learn more about where the sharks go once they reach adulthood. They may well move out of our sight to feed and breed in deeper offshore waters.”

Dinosaurs became extinct, sharks survived

This video from Canada says about itself:

Dr. Mike Newbrey, Royal Tyrrell Museum “The Effects of Climate Change on the Growth Biology and Geographic Distribution of Cretaceous Sharks.”

Originally published April 1, 2011.

From Uppsala University in Sweden:

The end-Cretaceous extinction unleashed modern shark diversity

August 2, 2018

A study that examined the shape of hundreds of fossilized shark teeth suggests that modern shark biodiversity was triggered by the end-Cretaceous mass extinction event, about 66 million years ago.

This finding is reported this week in Current Biology.

As part of a larger scientific endeavour aiming to understand the diversity of fossil sharks, a group of researchers from Uppsala University, Sweden, and the University of New England, Australia, have explored how certain groups of sharks responded to the mass extinction that killed-off non-bird dinosaurs and marked the end of the Cretaceous period and the Mesozoic era.

Much like several other vertebrate groups during the Cretaceous (142-66 million years ago), shark diversity looked very different from today. Ground sharks (Carcharhiniformes) are the most diverse shark group living today, with over 200 different species. However, while dinosaurs dominated terrestrial environments during the Cretaceous, Mackerel sharks (Lamniformes) were the dominant shark forms of the sea.

“Our study found that the shift from lamniform- to carcharhiniform-dominated assemblages may well have been the result of the end-Cretaceous mass extinction“, said project leader and Uppsala doctoral student Mohamad Bazzi.

Sharks are one of the major groups that survived the Cretaceous-Palaeogene mass extinction and, today, carcharhiniforms are typified by forms such as the Tiger, Hammerhead, and Blacktip Reef sharks and lamniforms by the Great White and Mako sharks.

“Unlike other vertebrates, the cartilaginous skeletons of sharks do not easily fossilize and so our knowledge of these fishes is largely limited to the thousands of isolated teeth they shed throughout their lives”, says Mr. Bazzi. “Fortunately, shark teeth can tell us a lot about their biology, including information about diet, which can shed light on the mechanisms behind their extinction and survival.”

The team used “cutting-edge” analytical techniques to explore the variation of tooth shape in carcharhiniforms and lamniforms and measured diversity by calculating the range of morphological variation, also called disparity.

“Going into this study, we knew that sharks underwent important losses in species richness across the extinction“, said Dr. Nicolás Campione at the University of New England, who co-devised the project. “But to our surprise, we found virtually no change in disparity across this major transition. This suggests to us that species richness and disparity may have been decoupled across this interval.”

Despite this seemingly stable pattern, the study found that extinction and survival patterns were substantially more complex. Morphologically, there were differential responses to extinction between lamniform and carcharhiniform sharks, with evidence for a selective extinction of lamniforms and a subsequent proliferation of carcharhiniforms (the largest order of living sharks today) in the immediate aftermath of the extinction.

“Carcharhiniforms are the most common shark group today and it would seem that the initial steps towards this dominance started approximately 66 million years ago”, said Mr. Bazzi, who remarks that further research is still needed to understand the diversity patterns of other shark groups, along with the relationship between diet and tooth morphology.

Although the mechanisms that triggered such a shift in sharks can be difficult to interpret. The team hypothesises that changes in food availability may have played an important role. The end-Cretaceous extinction saw to major losses in marine reptiles and cephalopods (e.g. squids) and the post-extinction world saw the rise of bony fishes. In addition, it is likely that the loss of apex predators (such as lamniforms and marine reptiles) benefited mid-trophic sharks, a role fulfilled by many carcharhiniforms.

“By studying their teeth, we are able to get a glimpse at the lives of extinct sharks”, said Dr. Campione, “and by understanding the mechanisms that have shaped their evolution in the past, perhaps we can provide some insights into how to mitigate further losses in current ecosystems.”

Approximately 50% of the shark species in the IUCN are considered to be either endangered, threatened, or near-threatened.

Stolen shark ‘Miss Helen’ found again

This video from Texas in the USA says about itself:

Stealing Nemo! – Suspect arrested for SHARK THEFT in San Antonio

31 July 2018

Mandatory Credit: San Antonio Aquarium

One suspect was arrested for shark theft from the San Antonio Aquarium on Monday, after CCTV footage from the robbery was published on social media on July 28, the same day the 16-inch (40-centimetre) shark called ‘Miss Helen’ was stolen.

As seen on the CCTV footage, a man pulls out Miss Helen by her tail, before wrapping her in a blanket, putting her in a child’s stroller, and driving away with what seems like his accomplice in a pick up truck.

Miss Helen was retrieved on Monday, after police stormed the house of a man in the vicinity of the San Antonio Aquarium, who reportedly “maintains an extensive collection of marine life.”

Leon Valley Police Chief Joseph Salvaggio reportedly said that the suspect’s house “looked like almost a mock-up of the San Antonio Aquarium.”

The two perpetrators have confessed.

Miss Helen is a grey horn shark.