Walking sharks discovery off Australia

This 20 January 2020 video is called New species of walking shark found in Indonesia.

From the University of Queensland in Australia:

Walking sharks discovered in the tropics

January 21, 2020

Four new species of tropical sharks that use their fins to walk are causing a stir in waters off northern Australia and New Guinea.

While that might strike fear into the hearts of some people, University of Queensland researchers say the only creatures with cause to worry are small fish and invertebrates.

The walking sharks were discovered during a 12-year study with Conservation International, the CSIRO, Florida Museum of Natural History, the Indonesian Institute of Sciences and Indonesian Ministry of Marine Affairs and Fisheries.

UQ’s Dr Christine Dudgeon said the ornately patterned sharks were the top predator on reefs during low tides when they used their fins to walk in very shallow water.

“At less than a metre long on average, walking sharks present no threat to people but their ability to withstand low oxygen environments and walk on their fins gives them a remarkable edge over their prey of small crustaceans and molluscs,” Dr Dudgeon said.

“These unique features are not shared with their closest relatives the bamboo sharks or more distant relatives in the carpet shark order including wobbegongs and whale sharks.

The four new species almost doubled the total number of known walking sharks to nine.

Dr Dudgeon said they live in coastal waters around northern Australia and the island of New Guinea, and occupy their own separate region.

“We estimated the connection between the species based on comparisons between their mitochondrial DNA which is passed down through the maternal lineage. This DNA codes for the mitochondria which are the parts of cells that transform oxygen and nutrients from food into energy for cells,” Dr Dudgeon said.

“Data suggests the new species evolved after the sharks moved away from their original population, became genetically isolated in new areas and developed into new species,” she said.

“They may have moved by swimming or walking on their fins, but it’s also possible they ‘hitched’ a ride on reefs moving westward across the top of New Guinea, about two million years ago.

“We believe there are more walking shark species still waiting to be discovered.”

Dr Dudgeon said future research would help researchers to better understand why the region was home to some of the greatest marine biodiversity on the planet.

How remora fishes hitchhike with sharks, whales

This June 2016 video says about itself:

Everything You Need to Know About Those Fish That Attach to Sharks

It’s called a remora, and you’ve probably seen it before. It attaches to fish and marine mammals all the time. But get this: It doesn’t attach with its mouth. It’s got a suction cup it wears as a hat.

From the New Jersey Institute of Technology in the USA:

Discovery reveals how remora fishes know when to hitch a ride aboard their hosts

January 15, 2020

Summary: Researchers have detailed the discovery of a tactile-sensory system stowed within the suction disc of remora, believed to enable the fish to acutely sense contact pressure with host surfaces and gauge ocean forces in order to determine when to initiate their attachment, as well as adjust their hold on hosts while traversing long distances.

Remoras are among the most successful marine hitchhikers, thanks to powerful suction discs that allow them to stay tightly fastened to the bodies of sharks, whales and other hosts despite incredible drag forces while traveling through the ocean. But how do these suckerfish sense the exact moment when they must “stick their landing” and board their speedy hosts in the first place?

A team of biologists at New Jersey Institute of Technology (NJIT), Friday Harbor Labs at University of Washington (FHL-UW) and The George Washington University (GWU) now offers an answer.

In findings published in the Journal of the Royal Society Open Science, researchers have detailed the discovery of a tactile-sensory system stowed within the suction disc of remora, believed to enable the fish to acutely sense contact pressure with host surfaces and gauge ocean forces in order to determine when to initiate their attachment, as well as adjust their hold on hosts while traversing long distances.

Specifically, the study describes the discovery of groupings of push-rod-like touch receptors, or mechanoreceptor complexes, embedded in the outer lip of the remora adhesive disc, which have been known to aid other organisms in responding to touch and shear forces.

Researchers say the finding marks the first time such touch-sensory complexes have been described in fishes, as the structure was previously only known in extant monotremes — platypus and echidnas.

“One of the wildest things about this work was not only finding a mechanoreceptor complex not previously known to fishes, but that the only other organisms known to possess them are monotremes,” said Brooke Flammang, NJIT professor of biological sciences and lead author of the study. “This is exciting because it shows how much we as integrative comparative biologists still have to learn about the sensory world of organisms.”

“When I was in graduate school, conventional wisdom was that fishes did not have such mechanoreceptors,” said Patricia Hernandez, one of the study’s authors at The George Washington University. “The discovery that these fishes share convergent receptors with echidnas is really exciting and points us in the right direction for discovering similar convergence in other fishes.”

While conducting various imaging studies to examine the head and disc of Echeneis naucrates, a common sharksucker remora, the team successfully identified the complexes: dome-like protrusions along the surface of the soft tissue lip surrounding the remora’s adhesive disc. Each dome packs below it a column of cells with three vesicle chains containing sensory nerves that stretch from the disc’s epidermal layer down to its dermal layer. In addition to sensing contact, these complexes are thought to respond to shear stress, which would provide feedback information to the remora if it was losing its grip and sliding backward on its host.

“When we first noticed these structures we were a little thrown off,” said Karly Cohen, a Ph.D. biology student at FHL-UW and an author on the study. “We knew they had to be sensory because of the plethora of nerves, but they didn’t look like lateral line structures, which are one of the main ways fishes sense their environment. We dove into the literature to try and find structures that fit the morphology of those we saw in the remora histology. Finally landing on the push-rod receptors known in echidnas was so exciting. … It was validation of the morphology we were seeing and it took us into a realm of mechnosensation that we were not necessarily considering when thinking about how the remora stick.”

Notably, in further examining seven other remora species, the team found that those species known to frequently piggyback on larger and faster hosts, like pelagic billfish, are equipped with nearly double the mechanoreceptor complexes of remora species that typically hitchhike on slower swimmers, such as reef fishes.

“On animals swimming very fast where the remora may be under increased drag conditions, the need to recognize loss of contact and make an instant correction is more crucial than on slower swimming hosts,” noted Flammang.

Flammang and colleagues say that the touch-signaling complexes found in remoras suggest not only that fishes may be able to sense their environment in ways not previously realized, but that specialized mechanoreceptors may also be a much more common feature among basal vertebrates than was previously thought as well.

“The interesting aspect here is that push-rods are only otherwise known in platypus and echidnas,” said Flammang. “Obviously, there is no close phylogenetic relationship between remoras and monotremes, so this likely means that there are a lot of mechanoreceptors in vertebrates that just haven’t been found in a wide breadth of organisms. We hope this paper brings this structure to the attention of other researchers for comparative study on how their organisms sense the environment.”

Great white sharks off Canada

This December 2019 video says about itself:

Todd Battis sits down with a team of researchers working to capture, tag, and track great white sharks off the coast of Atlantic Canada.

Ocean acidification could degrade sharks’ tough skin. Exposure to pH levels projected for 2300 damaged the denticles that make up sharkskin: here.

United States diver discovers megalodon shark teeth

This 5 October 2019 video from South Carolina in the USA says about itself:

I found huge megalodon shark teeth while scuba diving in the Cooper River. Huge thanks to Captain Alan Devier for putting us onto an amazing site. This was a very exciting diving adventure! I can’t wait to do this again! Who else enjoys finding shark teeth?

How great white sharks feed, new research

This 19 September 2019 video says about itself:

Wildlife expert Steve Backshall dives with the ocean’s ultimate predator, the Great White Shark, in the waters off Guadalupe Island, Mexico.

From the Research Organization of Information and Systems:

Technology provides insight into how white sharks hunt

October 2, 2019

White sharks are top predators in the marine environment, but unlike their terrestrial counterparts, very little is known about their predatory activity underwater, with current knowledge limited to surface predation events. Now, a team of international scientists has used video- and data-logging technology to shed new light on predator-prey interactions of these mighty sea creatures.

Their findings were published on July 4, 2019 in Marine Ecology Progress Series.

The white shark is an iconic species found in surface- and deep-waters in all major oceans of the world. With a lifespan that can stretch 70 years or more, these formidable predators can reach over six meters (20 feet) in size when fully mature. They prey on marine mammals, such as seals, as well as fish, and are responsible for more shark bites on humans than any other shark.

“Their breaching behavior — where they jump out of the water to catch seals — observed in South Africa, is especially famous, and has attracted the attention of a lot of people, including scientists,” said Yuuki Watanabe, associate professor in marine biology at the National Institute of Polar Research in Japan and lead author of the study.

“Although breaching behavior can be seen from boats and is well studied, what happens underwater is mostly unknown,” Watanabe added. “Moreover, in other aggregation sites of white sharks, including our study site in Australia, breaching behavior is rarely seen, suggesting that different hunting strategies are employed by these sharks.”

To gain a better understanding of the strategies white sharks use to scout and hunt their prey, the researchers needed to dive deeper — literally. “That’s why we decided to attach video cameras and other sensors to white sharks to directly observe their underwater hunting behavior on seals,” explained Watanabe, who has been engaged in biologging research for many years and has made unique discoveries about the ecology of marine life.

The international research team, including Watanabe and his colleague Charlie Huveneers (associated professor at Flinders University in Australia), lured sharks to their research boat by throwing ‘chum’ into the shark inhabited waters off Neptune Islands Marine Park in Australia. Chum, a fishy bait mixture consisting of fish blood and flesh, is very effective at attracting sharks due to their highly developed sense of smell. Using a deployment pole, metal clamps containing a data logging package were placed onto the front edge of the dorsal fins of eight white sharks. The data loggers included an accelerometer that recorded swim speed, depth and water temperature at one second intervals. It also recorded triaxial acceleration (measurements of body movement across three perpendicular axis) at shorter intervals. The data-logging package fitted onto three of the sharks also contained a tiny video camera, which recorded video footage for six hours at pre-programmed intervals. After 1-2 days, the data logger packages detached from the shark and were located and recovered on the surface using radio signals. The researchers then analyzed the accelerometer records and linked them to the video footage.

Acceleration data recorded by these devices allowed researchers to distinguish behavioral patterns while the animals were out of view by measuring tailbeat movement frequency.

“We obtained video footage showing how a white shark chased a seal in the water. In Japanese, we say ‘seeing is worth of a thousand words.’ This is also the case for ecological studies of marine animals,” said Watanabe.

The video footage showed one of the sharks attacking a seal. During this event, the attached data logger recorded intensive swimming action with a rapid burst in lateral acceleration, tailbeat frequency and swim speed. After analyzing 150 hours of recorded acceleration data, the researchers identified seven potential predation events at various depths ranging from the surface to a depth of 53 meters (174 feet). These predation events occurred both at nighttime and during the twilight hours of dawn and dusk, which partially contrasts with the breaching behavior observed by white sharks hunting seals in South African coastal waters that primarily occurs at dawn and dusk.

These findings suggest that white sharks do not only prey on seals on the surface (attacking from below after searching for a seal silhouetted against the surface, illuminated by the sunlight shining from above) with the momentum of their upward thrust causing them to leap into the air in a breaching motion, as observed in South Africa. At the study site in Australia, sharks also actively search and pursue seals in deeper waters, and this predatory activity is not limited to dawn and dusk but rather also occurs at night, suggesting that white sharks do not depend on vision to locate and hunt their prey.

The researchers would like to get more footage of seal-hunting behavior of sharks to understand variations. “It appears that hunting strategies of white sharks in South Africa are very different to those in Australia, and we would like to understand what kinds of factors (biological or non-biological) are driving the difference,” he explained.

How basking sharks dive, new research

This 2015 video says about itself:

Breaching Basking Sharks | World’s Weirdest

Basking sharks have weird ways of ridding themselves of parasites.

From the University of Exeter in England:

Basking sharks exhibit different diving behavior depending on the season

September 26, 2019

Tracking the world’s second-largest shark species has revealed that it moves to different depths depending on the time of year.

Basking sharks spend most of the summer months at the ocean’s surface, but dive to deeper depths in winter.

This seasonal variation in behaviour is likely caused by environmental conditions: sharks could be exploring different areas of the ocean to deal with changes in food abundance.

Basking sharks also perform “yo-yo” dives towards late winter and early spring. “Yo-yo” dives are rapid and repeated movements between deep and surface waters.

Whilst performing these dives, several of the studied sharks reached depths of over 1000 m, and two were tracked as far as 1500 m below the surface.

Dr Phil Doherty, a postdoctoral researcher at the University of Exeter’s Penryn Campus and lead author of the study, said: “We do not know exactly why the sharks are performing these dives. They may be sampling the water column in efforts to detect prey, or attempting to re-orientate themselves for navigation purposes.”

Dr Doherty and his colleagues from the University of Exeter teamed up with Scottish Natural Heritage, MarAlliance, Manx Basking Shark Watch and Wave Action to study how the movements and diving behaviour of basking sharks change throughout the year.

The team attached satellite tags to 32 of these gentle giants off the coast of Scotland from a boat and monitored their movements. The tags collected data on depth and temperature, along with ambient light levels, which can be used to estimate the sharks’ location each day.

The collected data reveal a seasonal change in diving behaviour, it also showed that basking sharks move to different depths depending on the time of day.

“We found that sharks spent most of the summer near the surface of the water, occupying the top few metres during the day, moving down to depths of 10-25 m at night. But in winter, they did the opposite, spending the majority of time between 50 and 250 m, but more often shallower during the night,” said Dr Doherty.

Moving to shallower depths during the day and diving down at night is referred to as “reverse diel vertical migration.” All three planktivorous sharks — basking sharks, whale sharks and megamouth sharks — have been shown to display this behaviour.

Scientists believe that it enables them to track their main food source, plankton. Like basking sharks, plankton can remain close to the ocean’s surface during the summer and move to deeper depths to over winter.

Dr Doherty and his team hope to use their study as a starting point for further investigations to identify “depth hotspots” of basking shark activity.

Dr Suzanne Henderson, from Scottish Natural Heritage, said: “It’s great to see further analysis and publication of the data collected in 2012-2014. Behaviour at depth is the most challenging to obtain and understand and this adds to that knowledge for basking sharks.”

Basking sharks are a protected species considered as “threatened” globally, with the north-east Atlantic population considered “endangered”. Understanding their diving behaviour and preferred depths could help determine where shark presence overlaps with different types of fishing gear.

This information could be used to reduce the risk of incidental catch of these sharks by commercial fisheries, although we don’t know to what extent these sharks are at risk in Scottish waters. It could also help inform conservation measures to better protect sharks and their habitat.