Marine Life & Conservation
Study solves deep diving devil rays’ warm brain mystery
A new study shows that devil rays dive nearly 2km below the ocean surface, making some of the deepest and fastest dives ever observed in the sea.
Scientists tracked 15 of the large, winged fish, previously thought to be surface dwellers, for several months.
In between their icy dives, they appear to bask near the surface to warm up.
The findings from the study offer an explanation for a mysterious mass of blood vessels, thought to keep the ray’s brain warm.
The front part of the animal’s skull is stuffed with a sponge-like mesh of large and small arteries. This network, called a rete mirabile, was discovered in the devil rays 30 years ago.
“It was a mystery as to why they had this system, which is a way of keeping brain activity high, even in a cold environment,” said Dr Simon Thorrold, an ocean ecologist at the Woods Hole Oceanographic Institution and the new paper’s lead author.
The scientists who discovered the rete mirabile in devil rays were so baffled by its presence in a warm-water species that they even suggested it might be working in the opposite direction from usual, helping cool the brain while the rays basked in the sun.
Dr Thorrold’s results appear to have solved that mystery. “We looked at the data and of course, it made complete sense.”
He believes the rays are feeding at the bottom of their remarkable dives, using a well-heated, active brain to forage for small fish that abound in deeper layers of the ocean.
To reveal the ray’s secret submarine lifestyle, Dr Thorrold and his colleagues tagged 15 Chilean devil rays (Mobula tarapacana) using special tags tethered to darts.
“We actually jump in the water and tag them ourselves,” he said. “We take a polespear, we swim down and deploy the tag. The animal’s not restrained in any way.”
The researchers don’t suffer either. “It’s pretty good work, right? Free-diving in the Azores.”
This autonomous Portuguese archipelago happens to be one of the best places to find these particular devil rays, since they congregate there in the summer, around the top of underwater mountains.
But then, in the autumn, they disappear. “We had no idea where they were going,” said Dr Thorrold. “We had an idea that they were moving a long way, perhaps several thousand kilometres.”
That was where the tags came in. These programmable gadgets recorded depth, light, temperature and position data for up to five months, before detaching themselves and bobbing to the surface, where they beamed their data back to the researchers via satellite.
Perhaps unsurprisingly, the rays all headed south, with several being tracked almost as far as the equator.
This was the first time devil ray migration had been recorded and the distances were as much as 3,800km. But it was the other measurements that got the team excited.
“The first thing I looked at was the temperature data,” said Dr Thorrold, “and I saw temperatures of about 4C – and this is an animal that’s supposed to be living in the tropics! I suspected there was probably a mistake.”
The depth data confirmed, however, that the freezing temperatures were a result of incredibly deep dives, typically lasting 60-90 minutes and reaching 1,848m beneath the waves.
Very few fish, among them whale sharks, have been shown to dive this deep, and the all-time record (2,992m) is currently held by a mammal: the beaked whale.
During the day (but not at night), the devil rays tend to loiter within 2m of the water surface for periods before and after their deepest expeditions. This suggests they are using the sun’s warmth to prepare and recover.
One ray plunged below 1,400m on six consecutive days – behaviour that places these devil rays “right at the limit” of known diving behaviour, according to Dr Thorrold.
What is more, they were fast. The rays swam downward at up to 22km/h (13mph), which is much faster than sharks and whales typically descend.
That speed is another surprise. Because the rays are negatively buoyant, they could simply allow themselves to sink, gliding with little effort to their deep-sea feast.
“Our rays are swimming basically as hard as they can, straight down,” said Dr Thorrold. He believes this is another strategy for keeping warm.
Heat generated by their muscles could be stored and used by the specialised brain blood supply, to keep brain function high in the icy depths.
Dr Thorrold says the new findings highlight how little is known about these deeper ecosystems.
“We’re hoping that the rays are going to lead us to some really interesting biology, at depth, that we wouldn’t necessarily have been able to find ourselves – but we can use the rays to lead us to the biologically interesting layers and zones within those depths,” he said.
“These rays, in effect, connect the surface, epipelagic layers in the ocean, with the mysterious deep.”
Source: bbc.co.uk/news
Marine Life & Conservation
Paul Watson Released as Denmark Blocks Japan’s Extradition Bid
Renowned anti-whaling activist Paul Watson has been released from custody in Greenland after spending five months in detention. Denmark’s Justice Ministry rejected Japan’s request for his extradition, citing insufficient guarantees that his time already served in custody would be credited against any potential sentence.
The 74-year-old Canadian-American was arrested on July 21 in Nuuk, Greenland’s capital, when his ship docked to refuel. His arrest was based on a 2012 Japanese warrant related to a 2010 encounter in Antarctic waters. Japan alleged Watson obstructed operations and caused damage to a whaling research ship during efforts to disrupt illegal whaling. Watson has consistently denied these claims, maintaining his commitment to marine conservation.
Denmark, which oversees extradition matters for Greenland, concluded that while the legal conditions for extradition were met, the lack of assurances from Japan regarding time-served credit made extradition untenable.
In a video shared by his foundation, Watson expressed gratitude and relief, saying, “After five months, it’s good to be out… and good to know they’re not sending me to Japan.” He added that the most difficult part of his time in custody was being separated from his two young sons.
Watson is a pioneering figure in marine conservation, known for founding the Captain Paul Watson Foundation in 2022 after decades of activism with the Sea Shepherd Conservation Society. His bold efforts to defend marine life have earned him widespread support, including from celebrities and conservationists. His work has also been featured in the acclaimed reality TV series Whale Wars.
Watson’s lawyer, Jonas Christoffersen, praised the decision, stating, “We are happy and relieved that Paul Watson is now free.” He added that Watson is eager to reunite with his family and continue his vital work.
The arrest occurred while Watson’s vessel, the M/Y John Paul DeJoria, was en route to the North Pacific with a team of 26 volunteers to intercept a Japanese whaling ship. His foundation described the arrest as politically motivated and emphasized that Watson’s actions were focused on ending illegal whaling practices.
Japan resumed commercial whaling in 2019 after leaving the International Whaling Commission, asserting that whale meat is a cultural tradition. Conservationists, however, continue to challenge these practices, highlighting their impact on marine ecosystems.
Despite the challenges, Watson remains steadfast in his mission to protect marine life and bring attention to whaling practices. His dedication to ocean conservation has made him a globally respected advocate for the environment.
Marine Life & Conservation
12 Days of Zero-Waste Fish-mas
This holiday period, the Marine Conservation Society, the UK’s leading ocean membership charity, invites you to make some simple changes to eating fish this Christmas to help our seas.
Dr Kenneth Bodles, Head of Fisheries and Aquaculture at the Marine Conservation Society, said, “During the festive season, our consumption increases, but so does waste. Sustainability isn’t just about where food comes from – it’s also about how you use it. By reducing waste and making the most out of your seafood, you’re not only taking steps to be more ocean-friendly, but can also help to cut costs during what is often one of the most expensive times of the year”.
The Marine Conservation Society has compiled twelve tips on how to consume seafood sustainably with zero-waste this Christmas:
Buy whole fish instead of fillets
Instead of fillets, consider buying whole fish such as salmon, hake, or lemon sole. By adopting a “nose to tail” approach with cooking, whole-baked fish not only feeds a crowd, but also helps to minimise waste and maximise sustainability by using up every part of the animal, including bones, skin, and fat.
Make fish stock
Leftover fish bones or shells can be put to good use by boiling them to make a nourishing fish stock or bisque. This can be frozen and preserved for later use and makes for a flavourful base in a soup.
Make your own fish pâté
Avoid waste by turning leftover fish, such as smoked mackerel or salmon, into a delicious pâté by blending with cream cheese and lemon. Perfect when paired with crackers.
The sustainability of salmon and mackerel varies depending on where and how it is caught or farmed. For more information on green-rated options, check the charity’s Good Fish Guide.
Buy frozen
By purchasing seafood that is frozen or vacuum-packed, this helps to reduce waste by extending the shelf life of your food.
Fish pie
If you’re wondering what to do with leftover cooked fish, why not opt for a classic fish pie with mashed potatoes, leeks, and a cheesy sauce? A sure crowd pleaser on Boxing Day.
Use the head
Don’t forget the fish head! The meat is incredibly tender and flavourful. The charity recommends a cod’s head curry or recreating Fallow’s renowned cod’s head in siracha butter.
By stretching your ingredients further, not only is this a more sustainable way to enjoy seafood, but also cost-effective by repurposing leftovers and cooking creatively.
Boxing Day brunch
Mix leftover kippers or smoked salmon with scrambled eggs for a tasty, zero-waste, Boxing Day brunch.
For best choice, make sure you buy kippers, or herring, from the North Sea and the North Irish Sea.
Zero-waste storage
A top tip from the Marine Conservation Society to avoid waste is freezing fish offcuts to save for future use.
Crisp up the skin
Even leftover fish skin can be turned into a quick savoury snack by crisping it up in an air fryer with a little olive oil and salt.
Anchovies two ways
Leftover anchovies can either be blended with butter to make a delicious anchovy butter or tossed into pasta for a hit of umami flavour.
The charity recommends opting for anchovies caught in the Bay of Biscay for best choice.
Fishcakes
For an easy, zero-waste meal, leftover seafood trimmings can be mixed with mash and fried in breadcrumbs to make fishcakes.
Pickled mussels
Try pickling mussels in 1:1 vinegar and water, with a dash of sugar for a sustainable, zero-waste snack that can be enjoyed well beyond the festive season.
Mussels farmed in the UK are a seafood superhero. Grown using low-impact methods and harvested by hand, they get all the food they need from the sea around them. This makes them one of the most sustainable, ocean-friendly, and cost-effective seafood options.
Players of People’s Postcode Lottery have raised £6.6M towards the Marine Conservation Society’s vital work in making seafood more sustainable.
Laura Chow, Head of Charities at People’s Postcode Lottery, said: “Fish is a festive favourite for many, but making sustainable choices when it comes to how we buy and eat seafood makes all the difference for our ocean. Support from players of People’s Postcode Lottery has helped the Marine Conservation Society further its sustainable seafood work, so that we can all enjoy healthier, better protected seas.”
The Marine Conservation Society encourages you to make sustainable seafood choices a year-round habit, not just for Christmas. To check how sustainable the seafood on your plate is, you can visit the charity’s Good Fish Guide. The Guide helps consumers and businesses identify the most sustainable seafood using a simple traffic light system, based on where and how species are caught or farmed. Green is the best choice, amber means improvements are needed, and red indicates fish to avoid buying.
Zero-waste gift idea
Why not embrace a zero-waste Christmas by gifting a membership to support marine conservation? It’s a meaningful, low-waste gift that helps protect our ocean for generations to come. Memberships start from as little as £5 a month – the price of a sandwich and drink from your local coffee shop.
Find the latest sustainable seafood advice for wild-caught and farmed seafood on the Good Fish Guide, downloadable to your phone from www.mcsuk.org/goodfishguide.
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