Great white sharks scared of killer whales


This video says about itself:

This Is The Biggest Great White Shark Ever Caught On Camera

Great white sharks are… big. Obviously. But a few years ago, divers met up with Deep Blue, probably the biggest great white shark ever caught on camera. So what do we know about the massive great white?

From the Monterey Bay Aquarium in the USA:

White sharks flee feeding areas when orcas present

Electronic tag data reveals white sharks do not return until following season; elephant seals benefit

April 16, 2019

Summary: New research challenges the notion that great white sharks are the most formidable predators in the ocean. The research team documented encounters between white sharks and orcas at Southeast Farallon Island off California. In every case examined by the researchers, white sharks fled the island when orcas arrived and didn’t return there until the following season. Elephant seal colonies in the Farallones also indirectly benefited from the interactions.

New research from Monterey Bay Aquarium and partner institutions published today in Nature Scientific Reports challenges the notion that great white sharks are the most formidable predators in the ocean. The study “Killer Whales Redistribute White Shark Foraging Pressure On Seals” shows how the great white hunter becomes the hunted, and the elephant seal, the common prey of sharks and orcas, emerges as the winner.

“When confronted by orcas, white sharks will immediately vacate their preferred hunting ground and will not return for up to a year, even though the orcas are only passing through,” said Dr. Salvador Jorgensen, senior research scientist at Monterey Bay Aquarium and lead author of the study.

The research team — which included Jorgensen and Monterey Bay Aquarium scientist Scot Anderson, and research partners from Stanford University, Point Blue Conservation Science and Montana State University — documented four encounters between the top predators at Southeast Farallon Island in the Greater Farallones National Marine Sanctuary, off San Francisco, California. The scientists analyzed the interactions using data from 165 white sharks tagged between 2006 and 2013, and compiled 27 years of seal, orca and shark surveys at the Farallones.

“The research in this paper combines two really robust data sources,” said Jim Tietz, co-author of the study and Farallon Program Biologist at Point Blue Conservation Science. “By supplementing the Aquarium’s new shark tagging data with Point Blue’s long-term monitoring of wildlife at the Farallon Islands National Wildlife Refuge, we were able to conclusively show how white sharks clear out of the area when the orcas show up.”

In every case examined by the researchers, white sharks fled the island when orcas arrived and didn’t return there until the following season.

Elephant seal colonies in the Farallones also indirectly benefited from the interactions. The data revealed four to seven times fewer predation events on elephant seals in the years white sharks left.

“On average we document around 40 elephant seal predation events by white sharks at Southeast Farallon Island each season,” Anderson said. “After orcas show up, we don’t see a single shark and there are no more kills.”

Each fall between September and December white sharks gather at the Farallones to hunt for young elephant seals, typically spending more than a month circling Southeast Farallon Island. Transient orcas also feed on elephant seals, but only show up occasionally at the island.

To determine when orcas and sharks co-occurred in the area, researchers compared data from the electronic shark tags with field observations of orca sightings. This made it possible to demonstrate the outcome on the rare instances when the predators encountered each other.

Electronic tags showed all white sharks began vacating the area within minutes following brief visits from orcas. Sometimes the orcas were only present for less than an hour. The tags then found the white sharks either crowded together at other elephant seal colonies farther along the coast or headed offshore.

“These are huge white sharks. Some are over 18 feet long (5.5 meters), and they usually rule the roost here,” Anderson said. “We’ve been observing some of these sharks for the past 15 to 20 years — and a few of them even longer than that.”

The study’s findings highlight the importance of interactions between top predators, which aren’t well-documented in the ocean.

“We don’t typically think about how fear and risk aversion might play a role in shaping where large predators hunt and how that influences ocean ecosystems,” Jorgensen said. “It turns out these risk effects are very strong even for large predators like white sharks — strong enough to redirect their hunting activity to less preferred but safer areas.”

The researchers drew no conclusions about whether orcas are targeting white sharks as prey or are bullying the competition for the calorie-rich elephant seals.

“I think this demonstrates how food chains are not always linear,” Jorgensen said. “So-called lateral interactions between top predators are fairly well known on land but are much harder to document in the ocean. And because this one happens so infrequently, it may take us a while longer to fully understand the dynamics.”

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Diver woman petting Bahamas sharks, video


This 29 March 2019 video says about itself:

Petting Sharks like Dogs?! | Blue Planet Live | BBC Earth

Cristina Zenato is the woman who isn’t afraid to hug sharks.

Cristina Zenato caresses her sharks in the warm Bahamas waters, the animals seem to like the suit’s touch on their skin and stop in her lap for a quick stroke.

Bahamas sharks, BBC video


This 26 March 2019 video says about itself:

Sharks in the Bahamas | Blue Planet Live | BBC Earth

Watch the new promo for Blue Planet Live! BBC One will air the program at 8 pm on Wednesday 27th March for the UK audience and BBC Earth will air at 3 pm for the Canada Audience.

Steve Backshall dives with tiger and hammerhead sharks in the Bahamas. Here shark fishing is illegal and the booming population helps the local economy by means of underwater tourism.

Diver meets sharks in Bahamas waters


This 19 March 2019 video says about itself:

Come face to face with several species of sharks at Tiger Beach, while on expedition with conservationist Jim Abernethy. Shark diving generates millions of dollars every year in the Bahamas, where the apex predators are protected by the government and there is a $5,000 fine for shark fishing.

Hammerhead sharks mating, video


This 19 March 2019 video says about itself:

The Complex world of Hammerhead Mating Rituals | BBC Earth

The Galapagos Islands are like no other place on Earth. 600 miles off the mainland of South America, this isolated archipelago lies in the heart of the Pacific Ocean. This investigation employs tagging technology, underwater mapping, cinematography, thermal cameras and other techniques to track the most mysterious creatures, solve unanswered riddles, explore ancient islands reclaimed by the sea, and encounter the islands’ volcanic underbelly.

Extinct Megalodon sharks’ teeth, new study


This 26 August 2018 video says about itself:

Did They Find a Living Megalodon In the Mariana Trench?

Сould Megalodon sharks still be alive in the deepest parts of the ocean? Science tells us that Megalodon sharks are extinct. Given that it was a massive shark with noticeable feeding habits, we guess that if Megalodon sharks were still roaming the oceans, they would probably have been spotted by someone by now.

From the Florida Museum of Natural History in the USA:

How megalodon‘s teeth evolved into the ‘ultimate cutting tools’

March 4, 2019

Megalodon, the largest shark that ever lived, is known only from its gigantic bladelike teeth, which can be more than 7 inches long. But these teeth, described by some scientists as the “ultimate cutting tools”, took millions of years to evolve into their final, iconic form.

Megalodon’s earliest ancestor, Otodus obliquus, sported three-pronged teeth that could have acted like a fork for grasping and tearing fast-moving fishes. In later megatooth shark species, teeth flattened and developed serrated edges, transitioning to a knifelike shape for killing and eating fleshy animals like whales and dolphins.

But the final tooth evolution in this lineage of powerful predators still took 12 million years, a new study shows. An analysis of teeth from megalodon and its immediate ancestor, Carcharocles chubutensis, traced the unusually slow, gradual shift from a large tooth flanked by mini-teeth — known as lateral cusplets — to teeth without these structures.

“This transition was a very long, drawn-out process, eventually resulting in the perfect cutting tool — a broad, flat tooth with uniform serrations”, said study lead author Victor Perez, a doctoral student in geology at the Florida Museum of Natural History. “It’s not yet clear why this process took millions of years and why this feature was lost.”

Teeth can offer a wealth of information about an animal, including clues about its age, when it lived, its diet and whether it had certain diseases. Megalodon‘s teeth suggest its hunting style was likely a single-strike tactic, designed to immobilize its prey and allow it to bleed out, Perez said.

“It would just become scavenging after that,” he said. “A shark wouldn’t want to grab and hold onto a whale because it’s going to thrash about and possibly injure the shark in the process.”

Perez and his collaborators carried out a “census of teeth”, analyzing 359 fossils with precise location information from the Calvert Cliffs on the western shore of Maryland’s Chesapeake Bay — an ocean in C. chubutensis and megalodon’s day. The cliffs provide an uninterrupted rock record from about 20 to 7.6 million years ago, a period that overlaps with these megatooth sharks.

The researchers noted a consistent decrease in the number of teeth with lateral cusplets over this timespan. About 87 percent of teeth from 20 to 17 million years ago had cusplets, falling to about 33 percent roughly 14.5 million years ago. By 7.6 million years, no fossil teeth had cusplets.

Adult C. chubutensis had cusplets while adult megalodon did not, but this feature is not a reliable identifier of which species a tooth belonged to, Perez said. Juvenile megalodon could have cusplets, making it impossible to discern whether a tooth with cusplets came from C. chubutensis or a young megalodon.

Some teeth analyzed for the study had tiny bumps or pronounced serrations where cusplets would be. A set of teeth from a single shark had cusplets on some, no cusplets on others and replacement teeth with reduced cusplets.

This is why paleontologists cannot pinpoint exactly when megalodon originated or when C. chubutensis went extinct, said Perez, who began the project as an intern at the Calvert Marine Museum.

“As paleontologists, we can’t look at DNA to tell us what is a distinct species. We have to make distinctions based off of physical characteristics,” he said. “We feel it’s impossible to make a clean distinction between these two species of sharks. In this study, we just focused on the evolution of this single trait over time.”

Lateral cusplets may have been used to grasp prey, Perez said, which could explain why they disappeared as these sharks shifted to a cutting style of feeding. Another possible function was preventing food from getting stuck between the sharks’ teeth, which could lead to gum disease. But if the cusplets served a purpose, why lose them?

“It’s still a mystery,” he said. “We’re wondering if something was tweaked in the genetic pathway of tooth development.”

Perez’s fascination with fossil sharks started at age 6 when he visited the Calvert Marine Museum.

“I got to take a shark tooth home from a discovery box. That set me off on the whole career path of studying fossils,” he said.

That first tooth spawned an obsession in Perez, who lived about an hour from the Calvert Cliffs. On family trips to the beaches on the north end of the cliffs, he spent his time combing the area for shark teeth.

“That was the only thing I wanted to do,” he said. “On a typical trip, I would leave with an average of 300 teeth.”

For this study, he relied on the efforts of fellow beachcombers: The vast majority of teeth analyzed in the study were discovered by amateur fossil collectors and donated to museum collections.

“This study is almost entirely built on the contributions of amateur, avocational paleontologists,” he said. “They are a valuable part of research.”

Fossil sharks, rays discovery in Madagascar


Eocene shark teeth from northwestern Madagascar. Credit: Samonds et al, 2019

From PLOS:

A rare assemblage of sharks and rays from nearshore environments of Eocene Madagascar

This finding, including one new shark species, fills a gap in the known marine record of Madagascar

February 27, 2019

Eocene-aged sediments of Madagascar contain a previously unknown fauna of sharks and rays, according to a study released February 27, 2019 in the open-access journal PLOS ONE by Karen Samonds of Northern Illinois University and colleagues. This newly-described fauna is the first report of sharks and rays of this age in Madagascar.

The Mahajanga basin of northwestern Madagascar yields abundant fossil remains of terrestrial and marine ecosystems, but little is known about fossil sharks and rays during the Eocene Epoch, 55-34 million years ago, in this region. This is in contrast to the numerous shark and ray faunas known from other Eocene sites around the globe, and to shark and ray ecosystems known from older and younger sediments in the Mahajanga basin.

In this study, Samonds and colleagues collected isolated teeth, dental plates, and stingray spines from ancient coastal sediments of the Ampazony and Katsepy regions of the basin, dated to the middle to late Eocene. They identified at least 10 species of sharks and rays, including one new species, Carcharhinus underwoodi. This is the oldest named species of Carcharhinus, a genus that has been globally distributed for the past 35 million years but is known only rarely from the Eocene.

Aside from the new species, the fauna of Eocene Madagascar shares many species with Eocene ecosystems across North Africa, suggesting these animals were widespread in southern seas at that time. On the other hand, the Madagascar fauna is uniquely lacking in sandsharks and dominated by eagle rays, indicating a somewhat unusual ecosystem, unsurprising given Madagascar’s long history of isolation. The authors caution that this study provides an incomplete picture given that they collected only fossils larger than 2 millimeters. They recommend that future studies target smaller material for a more complete view of the ancient ecosystem.