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Sharks and rays leap out of the water for many reasons, including feeding, courtship and communication

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Sharks and rays leap out of the water for many reasons, including feeding, courtship and communication


breaching shark
Credit: Pixabay/CC0 Public Domain

Many sharks and rays are known to breach, leaping fully or partly out of the water. In a recent study, colleagues and I reviewed research on breaching and ranked the most commonly hypothesized functions for it.

We found that removal of external parasites was the most frequently proposed explanation, followed by predators chasing their prey; predators concentrating or stunning their prey; males chasing females during courtship; and animals fleeing predators, such as a ray escaping from a hammerhead shark in shallow water.

We found that the highest percentage of breaches, measured by the number of studies that described it, occurred in manta rays and devil rays, followed by basking sharks and then by eagle rays and cownose rays. However, many other species of sharks, as well as sawfishes and stingrays, also perform this behavior.

Why it matters

It takes a lot of energy for a shark or ray to leap out of the water—especially a massive creature like a basking shark, which can grow up to 40 feet (12 meters) and weigh up to 5 tons (4.5 tonnes). Since the animal could use that energy for feeding or mating, breaching must serve some useful purpose.

Sharks that have been observed breaching include fast-swimming predatory species such as blacktip sharks and blue sharks. White sharks have been seen breaching while capturing seals in waters off South Africa and around the Farallon Islands off central California.

However, basking sharks—enormous, slow-swimming sharks that feed by filtering tiny plankton from seawater—also breach. So do many ray species, such as manta rays, which also are primarily filter feeders. This suggests that breaching likely serves different functions among different types of sharks and rays.

The most commonly proposed explanation for breaching in planktivores, like basking sharks and most rays, is that it helps dislodge parasites attached to their bodies. Basking sharks are known to host parasites, including common remoras and sea lampreys. The presence of fresh wounds on basking sharks that match the shape and size of a lamprey’s mouth suggests that breaching has torn the lampreys off the sharks’ bodies.

Other species may breach to communicate. For example, white sharks propelling themselves out of the water near the Farallon Islands may do so to deter other sharks from feeding upon the carcass of a seal.

Researchers have seen large groups of mantas and devil rays jumping together among dense schools of plankton—presumably to concentrate or stun the plankton so the rays can more easily scoop them up. Scientists have also suggested that planktivorous sharks and rays may breach to clear the prey-filtering structures in their gills.

Understanding more clearly when and how different types of sharks and rays breach can provide insights into these animals’ life habits, and into their interactions with their own species and competitors.

How we did our work

I worked with marine scientists Tobey Curtis, Emmett Johnston, Alison Kock and Guy Stevens. Across our various projects, we have seen breaching in bull sharks in Florida, basking sharks in Ireland, white sharks in South Africa and central California, and manta rays in the Maldives. Each of us has proposed different explanations for why the animals did it.

We reviewed scientific studies and video footage to see what species had been observed to breach, under what conditions, and the functions that other researchers had proposed for them doing so. This included information gathered from data logging tags attached to sharks and rays, digital photography, and imagery from underwater and aerial drones.

Our review proposes further studies that could provide more information about breaching in different species. For example, attaching data loggers to individual animals would help scientists measure how quickly a shark or ray accelerates as it propels itself out of the water.

Experiments in aquarium tanks could provide more insight into why the animals breach. For example, scientists could add remoras to a tank containing bull sharks, which can live in an aquarium environment, and observe how the sharks respond when remoras attach themselves to the sharks’ bodies.

In the field, researchers could play audio recordings of splashes from breaches to elicit withdrawal or attraction responses from sharks tagged with ultrasonic transmitters. There remains much to learn about why these animals spend precious energy jumping out of the water.

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This article is republished from The Conversation under a Creative Commons license. Read the original article.The Conversation

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Sharks and rays leap out of the water for many reasons, including feeding, courtship and communication (2024, September 23)
retrieved 23 September 2024
from https://phys.org/news/2024-09-sharks-rays-courtship-communication.html

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Telegram’s Durov announces new crackdown on illegal content

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Telegram’s Durov announces new crackdown on illegal content


Pavel Durov was arrested in France in August
Pavel Durov was arrested in France in August.

Telegram founder and chief executive Pavel Durov said Monday that the messaging platform had removed more “problematic content”, weeks after his arrest in France on charges of failing to act against criminals using the app.

Telegram’s search feature “has been abused by people who violated our terms of service to sell illegal goods”, Durov told the 13 million subscribers of his personal messaging channel.

“Over the past few weeks” staff had combed through Telegram using artificial intelligence to ensure “all the problematic content we identified in Search is no longer accessible”, he said.

Durov added that the platform had updated its terms of service and privacy policy to make clear that it would share infringers’ details with authorities—including internet IP addresses and phone numbers—”in response to valid legal requests”.

“We won’t let bad actors jeopardize the integrity of our platform for almost a billion users,” he said.

Durov was arrested on August 24 as he arrived at Le Bourget airport outside Paris on a private jet.

After days of questioning, he was charged with several counts of failing to curb extremist and terrorist content and released on a five-million-euro ($5.6 million) bail.

During the investigation he must remain in France and report to police twice a week.

Durov—who holds Russian, French and United Arab Emirates passports—initially criticized his arrest, but he has since announced steps appearing to bow to Paris’s demands.

On September 6, he said Telegram would alter its “people nearby” feature to present users with “legitimate businesses” rather than “bots and scammers”.

“This year we are committed to turn moderation on Telegram from an area of criticism into one of praise,” he said at the time.

Durov, an enigmatic figure who rarely speaks in public, has a fortune estimated at $15.5 billion by Forbes magazine, but touts the virtues of an ascetic life that includes ice baths and not drinking alcohol or coffee.

© 2024 AFP

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Telegram’s Durov announces new crackdown on illegal content (2024, September 23)
retrieved 23 September 2024
from https://techxplore.com/news/2024-09-telegram-durov-crackdown-illegal-content.html

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Indigenous outback rangers in WA find up to 50 night parrots, among Australia’s most elusive birds

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Indigenous outback rangers in WA find up to 50 night parrots, among Australia’s most elusive birds


Indigenous outback rangers in WA find up to 50 night parrots, among Australia's most elusive birds
The night parrot lives in arid inland Australia. Pictured: an 1890 illustration by Elizabeth Gould. Credit: Wikimedia, CC BY

In arid inland Australia lives one of Australia’s rarest birds: the night parrot. Missing for more than a century, a live population was rediscovered in 2013. But the species remains elusive.

Until recently, Australia’s known night parrot population numbered in the tens of birds, scattered across desert in Queensland and Western Australia.

But our research team—consisting of Indigenous rangers and scientists—has made a breakthrough discovery. We’ve detected the largest known night parrot population in the world: perhaps as many as 50, living in WA’s Great Sandy Desert, on land managed by the Ngururrpa people. Our results are published today.

Urgent action is needed to protect these vulnerable populations and ensure the night parrot doesn’t go missing a second time, perhaps for good.

A highly mysterious species

The night parrot was once found throughout Australia’s arid inland, but its numbers plummeted in the late 19th century.

The bird was not definitely recorded for more than 100 years, until a dead bird was found near Boulia in western Queensland in 1990. Another dead bird was found in Diamantina National Park, also in western Queensland, in 2006.

In 2013 a small population was found by naturalist John Young in south-western Queensland. That area is now a wildlife reserve.

Night parrots are notoriously difficult to detect. They build tunnels in dense spinifex and hide there by day, emerging at night to forage. They are known only from populations in remote south-west Queensland and central and northern Western Australia. The species is critically endangered.

In Western Australia, Indigenous cultural knowledge about the species includes stories about how difficult the bird is to find. There are also whispered stories of mothers telling children the night parrot’s call was the sound of an evil spirit, and warning them not to stray from camp.






A short video explaining the night parrot project.

What we did

The Ngururrpa Indigenous Protected Area is in the Great Sandy Desert. It comprises vast areas of sandplains and dunefields, and smaller areas of floodplain and spinifex which are key night parrot habitats.

Ngururrpa Rangers worked with scientists to learn how to use sound recorders to search for night parrots. We then searched for the birds on Country between 2018 and 2023.

We combined the rangers’ detailed knowledge of habitats, water and seed resources with geology maps, satellite imagery and fire history data. From this we selected 31 potential roosting areas, then deployed sound recorders called “songmeters” at those sites.

We wanted to detect the night parrots’ distinctive calls which consist of whistles, croaks and bell-like sounds.

The acoustic data we gathered was then analyzed to extract any bird calls in the night parrot’s frequency range. Potential detections were verified using a reference library of known night parrot calls.

Our results

We detected night parrot calls at 17 of 31 sites. Of these, ten were roost sites, where night parrot calls were detected in the hour after sunset and the hour before sunrise.

Individual night parrots are thought to have unique calls. We analyzed how many different calls we could hear, and how loud they were (which can tell us when birds are calling from different locations). From this we built a picture of the identity and number of individuals regularly occupying a site.

We extrapolated this across the 58 patches of potential night parrot habitat on the Ngururrpa Indigenous Protected Area. We concluded up to 20 roosting areas may be occupied by night parrots.

Based on the numbers at roosting sites where we recorded calls, we estimate 40–50 night parrots could be present in the Ngururrpa Indigenous Protected Area.

Fire and predators pose grave threats

Once we found the night parrot populations, we wanted to know what threats they faced.

We used camera-traps to identify predators and also collected their scats (poos) to analyze their diets.

Dingoes were the predator detected most frequently in night parrot roosting habitat. Our cameras captured them ten times more often than feral cats. And we found dingoes regularly eat feral cats at night parrot sites.

Based on information from other areas, we suspect cats are a key predator of night parrots. Dingoes could be important in suppressing cat numbers and helping the parrots survive. So, attempts to limit predators in night parrot habitat should not harm dingoes.

We also analyzed 40 years of satellite imagery to assess the threat of fire to night parrots’ roosting habitat. Based on the vegetation types and flammability of surrounding landscapes, we found bushfires sparked by lightning are a much bigger threat to night parrots in the Great Sandy Desert than in Queensland.

Strategic aerial and ground burning, to reduce fuel loads, already occurs in the Ngururrpa Indigenous Protected Area. As our knowledge of night parrots improves, these programs can become more targeted to protect key night parrot areas.

Keeping night parrots alive

A long-term monitoring program for night parrots on Ngururrpa Country should be established to help better understand and protect this vitally important population.

And the remote, wild nature of the landscape should be retained. This means minimizing disturbance from people and vehicles, and continuing to exclude livestock and weeds.

Ngururrpa Ranger Clifford Sunfly exlpains how rangers want to help protect night parrots into the future: “We would like to spend more time on Country to find where [night parrots] are and understand what they are doing. We want those scientists to come and help us catch some night parrots and tag them. We also need more snake-cams (inspection cameras) too and more songmeters. And a kit for collecting scats for DNA. One day we would love to have our own research facility for doing our night parrot surveys. It would be our dream to have our own research base on Ngururrpa.”

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This article is republished from The Conversation under a Creative Commons license. Read the original article.The Conversation

Citation:
Indigenous outback rangers in WA find up to 50 night parrots, among Australia’s most elusive birds (2024, September 23)
retrieved 23 September 2024
from https://phys.org/news/2024-09-indigenous-outback-rangers-wa-night.html

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Could a wealth tax help reduce inequality?

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Could a wealth tax help reduce inequality?


tax
Credit: CC0 Public Domain

The idea of taxing personal fortunes is under increasing discussion amid the growing disparity in wealth distribution in society.

It’s not in your imagination—the gap between the wealthy and everyone else is growing.

Research by ACOSS and UNSW Sydney shows that the average wealth of Australia’s highest 10% is growing much faster than the lowest 60%. And now, nearly half of all wealth is held by the top 10% of households. So, as the rich get richer and the rest face a seemingly uphill battle to stay afloat, do we need to find ways to rebalance the economic scales?

Associate Professor Bruce Bradbury from the Social Policy Research Center at UNSW Arts, Design & Architecture says wealth inequality—that is, the unequal distribution of wealth in society—is coming under increasing public scrutiny.

“For a long time, interest in inequality has tended to focus on income and ability to consume, but now there’s an increasing focus on what role wealth plays in determining opportunities,” A/Prof. Bradbury says. “And as wealth has become more and more concentrated, that’s caught the eye of more people as a marker of disparity.”

Emeritus Professor Chris Evans, School of Accounting, Auditing & Taxation at UNSW Business School, says there will always be differences in wealth—and wealth inequality, up until a point, isn’t inherently problematic. It is when wealth is too unequally distributed that it can lead to the concentration of economic power and opportunities in the hands of just a few at the top, while those at the bottom are left out.

“It’s when there is gross inequality in wealth that it is a disaster for social cohesion because it unfairly limits opportunities for those less well-off to fulfill their potential,” Prof. Evans says. “So, there is certainly an argument for using some of the excess money at the top end to help some of the people at the bottom, and we might just find that we’ll have a much fairer and more efficient society.”

Taxing wealth at the top

The premise of a wealth tax is to take a small portion of the large amount of money tied up in the fortunes of wealthy individuals and redirect it towards those less well-off via taxation. Governments can then use the revenue raised from the tax to close the wealth inequality gap by improving essential services like education, building more social housing, or increasing supplements for low-income households.

One method of doing this is through an annual net worth tax—a small recurrent financial charge imposed on the value of a person’s wealth (the sum of assets minus their liabilities). It differs from income tax, which is the levy charged on the money received from work or through investments, and arguably provides a more complete picture of their financial power.

A variation of a net worth tax called a billionaire’s tax works similarly in principle but is levied on the highest-net-worth individuals. The idea for a global minimum tax on billionaires of 2% already has some support in principle from countries like Brazil, South Africa, and Germany.

Supporters of net wealth taxes argue it’s fair that the wealthiest have the means and should contribute more, Prof. Evans says. Critics say it unfairly punishes success, could discourage innovation, and lead the rich to move their investments to countries with more favorable tax laws.

“For Australia to introduce a net wealth tax, it would likely need to be either a progressive rate or very modest rate and have a very high threshold to hope to work,” Prof. Evans says. “So, it should probably be less than 1% tax and only for those in the 99th%ile of wealth.

“But even so, it would still need to overcome some complexities to be administered.”

Challenges to implementing a net-worth tax

Implementing a net worth tax in practice is easier said than done. While net worth taxes were once commonplace in the OECD, most have abandoned them due to disclosure, valuation, and mobility challenges.

“Net wealth taxes tend to be very easily evaded as lots of assets are hard to identify or value,” Prof. Evans says. “For example, hiding assets like cryptocurrency is easy; property must be valued yearly, which is a significant undertaking; and many shares are held in private firms with no disclosed market value.”

Some assets are also difficult to convert into money quickly to pay for a new tax.

“Some forms of wealth are just not very liquid,” A/Prof. Bradbury says. “Some people may have one main asset like a valuable property but don’t have much by way of income, so they wouldn’t have a way to pay a net wealth tax.”

All these challenges are manageable, but they require more robust solutions. For example, Prof. Evans says insurance companies could tackle disclosure and valuation by revealing what assets are insured and for what value.

“It sounds like an intrusion, but we already do this with banks who disclose to the ATO the interest they’re paying out to people,” Prof. Evans says. “You can also use good proxies for valuation, such as whatever it costs, and adjust for inflation each year.”

Prof. Evans says wealthy individuals would still have access to the best accountants and asset managers to minimize their tax bills. Still, even if a net wealth tax wasn’t effective in raising revenue, it may send a message to wealthy individuals about the need to contribute a fair share.

The estimated effective tax rate on the wealth held by billionaires worldwide is currently just 0.3%.

“The more non-compliance, the less valuable a tax becomes for raising revenues,” Prof. Evans says. “The few countries that have them now, like Spain, are only raising a small fraction of what they should be in theory.

“Even Switzerland, which has had a reasonably successful annual wealth tax in place in its cantons for many years, raises a relatively insignificant amount of its total tax by taxing wealth.”

Reforming other taxes on wealth

Wealth taxes could bring sufficient revenue to address inequality in a perfect world. But if they don’t work that way in practice, there are some alternatives.

Prof. Evans argues that the next best idea could be reintroducing an inheritance tax—a levy placed on the value of a person’s estate that would be payable at death.

“There is an argument that inheritance tax is fairer in some ways than a net wealth tax because the deceased no longer need their assets,” Prof. Evans says. “The way to tax it would be at a certain threshold, such as the increase on the value of the assets.”

An inheritance tax would also overcome some challenges plaguing the administration of net worth taxes.

“Because the beneficiaries want to know the assets and their value, the valuation and disclosure problems are gone,” Prof. Evans says. “Any liquidity problems are also solved because the assets are sold off as part of the process, or there could be exemptions for spouses or direct relatives with the family home.”

A/Prof. Bradbury says another alternative could be to reshape property taxation by reforming stamp duty to make it work like a tax on land value. It would be particularly effective for raising revenue in Australia, where a significant amount of personal wealth is tied up in real estate.

“A one-off stamp duty transfer levy when a property is purchased is inefficient because it discourages people from moving,” A/Prof. Bradbury says. “Instead, proper land valuations and property taxes paid annually rather than in one lump sum would raise more revenue over time.”

Likelihood of introducing a wealth tax

A/Prof. Bradbury says back home, changes to any tax regime targeting wealth will likely receive significant pushback from some quarters.

“The losers in any tax change tend to make more noise than the winners benefiting,” A/Prof. Bradbury says. “And in this case, the losers likely have significant political influence.”

Prof. Evans agrees, saying it would be a daring move for any government to pull off a form of wealth tax, at least in the short term.

“The public is becoming more receptive to it, but introducing a wealth tax of any kind is still not likely to be popular politically,” Prof. Evans says. “It would take a courageous government with a big majority to attempt it, and there would be big scare campaigns to shut it down.”

While no perfect solution exists, Prof. Evans says more action to tackle wealth inequality should be welcomed.

“As the problem of wealth inequality gets worse, solutions that once seemed pie in the sky may become more palatable and even necessary,” Prof. Evans says. “Ultimately, if there are reforms, I hope we end up with a fairer and more efficient taxation system for all as a result.”

Citation:
Could a wealth tax help reduce inequality? (2024, September 23)
retrieved 23 September 2024
from https://phys.org/news/2024-09-wealth-tax-inequality.html

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High-pressure reactions can turn nonporous rocks into sponges

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High-pressure reactions can turn nonporous rocks into sponges


High-pressure reactions can turn nonporous rocks into sponges
Photographs of natural rocks showing (a) hydration and (b) dehydration features. (a) Eclogite shear zone with eclogitization associated to deformation from Holsnøy, western Norway (60°35’11”N, 5°07’34”E). (b) Metamorphic olivine veins in antigorite serpentinite from the Erro Tobbio ultramafic rocks, Ligurian Alps, Italy (44°33’38.9″N, 8°48’49.5″E). Credit: Geochemistry, Geophysics, Geosystems (2024). DOI: 10.1029/2023GC011422

In deep Earth, rocks take up and release water all the time, and the effects can be wide reaching. Dehydration can cause rocks to crack and trigger earthquakes, and over geologic timescales, this water cycling can influence plate tectonics and move continents.

Schmalholz and team asked how water can move through impermeable rocks, such as those found in mantle wedges, the deep lithosphere, and the lower crust. They hypothesize that certain reactions can cause temporary porosity in these rocks. By mathematically modeling the hydration and dehydration of rock at high pressure, they derived equations to estimate how the porosity of rock changes as water cycles through it.

The research is published in the journal Geochemistry, Geophysics, Geosystems.

Previous work suggested that at very high temperatures, minerals can react with each other to form denser minerals, squeezing water out of the minerals and generating less dense, more porous rocks in the process.

As the reaction progresses, a “dehydration front” moves through the rock. On the other hand, some reactions cause rocks to act like dry sponges, soaking up surrounding water and becoming denser. The progression of this reaction is known as a hydration front.

In the study, the researchers presented 1D simulations for three scenarios (one for a hydration front and two for dehydration fronts) in which a rock with no porosity becomes temporarily porous.

In a hydration reaction, water flows into the rock from an external source, so the hydration front always moves in the same direction as the fluid is flowing. Dehydration reactions have two possible scenarios. In simple dehydration, water flows out of the rock and into the surrounding environment, moving in the opposite direction of the dehydration front.

In the second scenario, called dehydration inflow, water is squeezed out of minerals, and additional water flows in to fill up the created porosity, so the fluid moves in the same direction as the dehydration front.

Whichever direction water is pushed, it has the potential to enter impermeable surrounding rocks if the reactions generate a porosity that allows for it. Describing how water moves through deep Earth is challenging, the researchers note, but their newly derived equations provide a framework for others researching how water drives geological processes beneath Earth’s surface.

More information:
Stefan M. Schmalholz et al, (De)hydration Front Propagation Into Zero‐Permeability Rock, Geochemistry, Geophysics, Geosystems (2024). DOI: 10.1029/2023GC011422

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original storyhere.

Citation:
High-pressure reactions can turn nonporous rocks into sponges (2024, September 23)
retrieved 23 September 2024
from https://phys.org/news/2024-09-high-pressure-reactions-nonporous-sponges.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.





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