A GREAT white shark was last night feared to be in the English Channel after another man-eater was savaged.
A 5ft blue shark washed up on a beach had a giant bite mark, suggesting it had been attacked by an even bigger predator.
A dog walker who discovered the dead shark sent pictures to experts who said it could have been attacked by a Jaws-like killer.
Vet nurse Nikki Lambert, 27, who found it on Camber Sands in East Sussex and emailed photos to the Marine Conservation Society, said: ““It had a hole just behind its flipper through which you could see its internal organs.
“I was told that the only animals who would attack a blue shark like this would be a great white shark or a killer whale.
“But I suppose it’s possible the wound was made after it was dead by a dog or birds.”
Blue sharks, which can grow to 12ft and have killed humans, have previously been found off England’s west coast.
There has been no confirmed great white sighting in British waters but, with warmer seas, Richard Peirce of the Shark Trust said there was a “good chance” they would stray here.
Read more: http://www.mirror.co.uk/mobile/topnews/2011/11/05/great-white-shark-feared-to-be-in-english-channel-115875-23538753/#ixzz1cvuIGFeM
Showing posts with label Great white shark. Show all posts
Showing posts with label Great white shark. Show all posts
Sunday, November 6, 2011
Friday, November 4, 2011
RIP: Monterey Bay Aquarium Great White Shark Dies Minutes After Being Returned to Ocean; Staff 'Surprised And Saddened', 'Distressed and Puzzled'
MONTEREY, California -- The Monterey Bay Aquarium is deeply saddened to announce the death of the young great white shark released nine days ago off the coast of southern California.
"This is a very difficult day for all of us, and for everyone who saw and cared about this animal," said Jon Hoech, the aquarium's director of husbandry. "Based on the shark's behavior and condition prior to release, we had every confidence that he'd do well back in the wild. Unfortunately, that's not how things turned out. We're surprised and saddened by the outcome."
The 4-foot, 10-inch, 52-pound shark, was transported south to Goleta (Santa Barbara County) by the aquarium's animal care staff on October 25 and released that afternoon. He appeared to be doing well before the release team lost sight of him as he swam away, Hoech said. According to data from the electronic tracking tag, he died minutes after being released.
The electronic tag he carried popped free on Saturday, October 29; began transmitting its stored data on Sunday, October 30; and was recovered that afternoon. It was delivered to the aquarium's white shark team on Tuesday, November 1 for analysis.
"Our animal care staff is unrivaled in its knowledge of young great white sharks," said Jim Hekkers, the aquarium's managing director. "I'm proud of the passion and dedication they demonstrate each day. This is a difficult time for all of us."
The decision to release the shark after 55 days on exhibit was based on changes in how well he was navigating in the exhibit, said aquarium staff veterinarian Dr. Mike Murray – changes that, over time, could result in abrasions that might become a source of infection.
This was not the first time a great white shark on exhibit at the aquarium has experienced "navigation" problems. Back in February 2005, the aquarium released its great white shortly after UnderwaterTimes.com and the Pelagic Shark Research Foundation published exclusive pictures showing the shark with a severely abraded nose. Again in January 2007, the aquarium had to release its captive great white shark citing "snout abrasions" and "logistical challenges" in keeping the wild animal.
"Our first concern is always the health and well-being of the animals under our care," he said. "It became clear that it was time to release him."
Read on ...
Thursday, September 1, 2011
Great white sharks 'could be in British waters'
Great white sharks could be "occasional vagrant visitors" to waters around the British Isles, according to an expert.
Richard Peirce, chairman of the Shark Trust, said the conditions and availability of prey made British waters an ideal hunting ground for the feared predator.
Mr Peirce said: "The real surprise is that we don't have an established white shark population, because the conditions here mirror those in parts of South Africa, Australia and northern California.
"Research has shown that white sharks tolerate water temperatures in a range which would make British waters perfectly suitable for this species."
British waters are home to many species of predatory sharks including blue and mako sharks which have been spotted off southwest England in the summer and threshers and porbeagles which are year-round residents.
There have also been sightings of other sharks in British waters over the summer. Earlier this month fisherman Jim Millar spotted a 15ft (4.5m) thresher shark off Dartmouth in Devon, where they are very rarely seen.
Another fisherman caught a 300lb (21 stone) porbeagle shark off the coast of Donegal, Republic of Ireland, last month.
And there were two separate sightings of what was believed to have been an oceanic whitetip shark, a species also known to attack humans, in St Ives, Cornwall, in June, although very few shark experts believe the sightings were oceanic whitetips.
Mr Peirce believes it is only a matter of time before proof is found that the species at the top of the marine food chain, the great white shark - Carcharodon carcharias - is occasionally present in British waters.
"Great whites are highly nomadic in movement around the north Atlantic so it's reasonable to say there's a good chance they may stray into British waters.
"I do suspect we do get the occasional vagrant visitor."
Mr Peirce claims he almost proved there is a great white occurrence in the UK with a photograph of a shark caught off the north east coast of Scotland.
"I sent the photo to some of the world's leading experts but as soon as they heard it was caught off Scotland they started looking at what else it could be."
Mr Peirce has investigated more than 80 reported sightings of great whites in British waters over the past 14 years but only seven were found to be credible.
'Compelling evidence'
A fisherman in Cornwall reported a great white sticking its head out of the water - known as "spy-hopping" - in the 1970s and fishermen onboard three different boats, also off Cornwall, described a sighting of a great white within three weeks of one another in 1999.
Mr Peirce said: "The reason the evidence is so compelling is that it's from independent witnesses who do not know each other on different boats.
"The problem is these things happen in a flash. Unless the shark jumps right out of the water or is caught, all we'll see is a dorsal fin sticking out the water.
"The closest capture of a great white was off La Rochelle (in western France) about 200 nautical miles from UK shores which is no distance to them."
However Dr Russell Wynn, co-ordinator of the SeaWatch SW project and a senior marine scientist at the National Oceanography Centre in Southampton, said the odds of a great white being found in British waters were extremely low as the creatures are very rare in the northeast Atlantic.
The SeaWatch SW survey team has spent more than 5,000 hours scanning the seas off southwest England in the past five years but the only predatory sharks seen have been single blues and threshers.
"The only large shark the public are likely to see is the harmless plankton-feeding basking shark, which can grow to over 10m long and is occasionally seen leaping out of the water," he said.
But Dr Wynn accepted there was a small chance of a great white sighting off the British coast.
"It's certainly not impossible that a great white could be seen or caught in British waters one day, as we know they occur off southwest Europe in very low numbers."
But despite the recent sightings, the opportunity of seeing sharks is decreasing year on year.
Research carried out by Dalhousie University, Nova Scotia, Canada, in the Western Atlantic indicate serious depletions of more than 50% for many shark species.
Mr Peirce said: "Unless we do something about shark mortality in the Atlantic we won't be having this conversation in 50 years time."
http://www.bbc.co.uk/news/uk-england-14657123
Richard Peirce, chairman of the Shark Trust, said the conditions and availability of prey made British waters an ideal hunting ground for the feared predator.
Mr Peirce said: "The real surprise is that we don't have an established white shark population, because the conditions here mirror those in parts of South Africa, Australia and northern California.
"Research has shown that white sharks tolerate water temperatures in a range which would make British waters perfectly suitable for this species."
British waters are home to many species of predatory sharks including blue and mako sharks which have been spotted off southwest England in the summer and threshers and porbeagles which are year-round residents.
There have also been sightings of other sharks in British waters over the summer. Earlier this month fisherman Jim Millar spotted a 15ft (4.5m) thresher shark off Dartmouth in Devon, where they are very rarely seen.
Another fisherman caught a 300lb (21 stone) porbeagle shark off the coast of Donegal, Republic of Ireland, last month.
And there were two separate sightings of what was believed to have been an oceanic whitetip shark, a species also known to attack humans, in St Ives, Cornwall, in June, although very few shark experts believe the sightings were oceanic whitetips.
Mr Peirce believes it is only a matter of time before proof is found that the species at the top of the marine food chain, the great white shark - Carcharodon carcharias - is occasionally present in British waters.
"Great whites are highly nomadic in movement around the north Atlantic so it's reasonable to say there's a good chance they may stray into British waters.
"I do suspect we do get the occasional vagrant visitor."
Mr Peirce claims he almost proved there is a great white occurrence in the UK with a photograph of a shark caught off the north east coast of Scotland.
"I sent the photo to some of the world's leading experts but as soon as they heard it was caught off Scotland they started looking at what else it could be."
Mr Peirce has investigated more than 80 reported sightings of great whites in British waters over the past 14 years but only seven were found to be credible.
'Compelling evidence'
A fisherman in Cornwall reported a great white sticking its head out of the water - known as "spy-hopping" - in the 1970s and fishermen onboard three different boats, also off Cornwall, described a sighting of a great white within three weeks of one another in 1999.
Mr Peirce said: "The reason the evidence is so compelling is that it's from independent witnesses who do not know each other on different boats.
"The problem is these things happen in a flash. Unless the shark jumps right out of the water or is caught, all we'll see is a dorsal fin sticking out the water.
"The closest capture of a great white was off La Rochelle (in western France) about 200 nautical miles from UK shores which is no distance to them."
However Dr Russell Wynn, co-ordinator of the SeaWatch SW project and a senior marine scientist at the National Oceanography Centre in Southampton, said the odds of a great white being found in British waters were extremely low as the creatures are very rare in the northeast Atlantic.
The SeaWatch SW survey team has spent more than 5,000 hours scanning the seas off southwest England in the past five years but the only predatory sharks seen have been single blues and threshers.
"The only large shark the public are likely to see is the harmless plankton-feeding basking shark, which can grow to over 10m long and is occasionally seen leaping out of the water," he said.
But Dr Wynn accepted there was a small chance of a great white sighting off the British coast.
"It's certainly not impossible that a great white could be seen or caught in British waters one day, as we know they occur off southwest Europe in very low numbers."
But despite the recent sightings, the opportunity of seeing sharks is decreasing year on year.
Research carried out by Dalhousie University, Nova Scotia, Canada, in the Western Atlantic indicate serious depletions of more than 50% for many shark species.
Mr Peirce said: "Unless we do something about shark mortality in the Atlantic we won't be having this conversation in 50 years time."
http://www.bbc.co.uk/news/uk-england-14657123
Thursday, July 21, 2011
Great white sharks amass off Martha's Vineyard
Gathering by the shores of Monomoy Island near Martha's Vineyard, where much of the movie "Jaws" was filmed, great white sharks have people on notice in the Northeast.
The sharks make a pilgrimage to this region every year to feed, but a particularly large gray seal population has become an enticing magnet for the large, toothy predators. The presence of the sharks has created a booming tourism business as well as some jitters in the area.
"Gray seals have a lot of blubber and meat, so they are a high efficiency preferred menu item of great white sharks," New England Aquarium spokesperson Tony LaCasse told Discovery News. "Somehow the word is out in the great white world that this is the place to be."
He added, "Humans are not on their menu because we are a completely inefficient meal, since great white sharks are looking for maximum calories per kill."
Federal protection of marine mammals has been in place since 1972, and has led to the recovery of gray seals in the area, which are larger and fattier than Harbor seals that are in the waters off of Cape Cod. LaCasse suspects it took this long for gray seals to build up their population.
When seal numbers were down, the great white sharks mostly fed on dead whale carcasses, called "floaters." LaCasse said just this May, a fisherman went to explore a dead Minke whale near Martha's Vineyard and was surprised by a great white shark that swam out from under the whale "and checked him out.” The fisherman escaped without injuries.
Monomoy Island, where the great whites have been spotted, is an 8-mile spit of sand extending southwest from Cape Cod, and a national wildlife refuge, where access is limited. This has helped to keep people safe from the sharks. A booming tourism industry, with great white sharks as the No. 1 draw, has emerged in nearby Chatham, Mass. Tourism dollars are down by 4 percent in the Cape as a whole, but Chatham has seen a 15 percent uptick, especially now that it's the summer vacation season. LaCasse said during one recent tour, "a great white took a free-swimming seal" in a bloody, violent battle viewed by families riveted to the real life event.
Recent research supports the rise in great white shark numbers off of Cape Cod. A tagging project led by Greg Skomal of the Massachusetts Division of Marine Fisheries (DMF), succeeded in tagging six white sharks, ranging from 10 to 18 feet in length, off the coast of Monomoy Island. The DMF notes there has been a "recent increase in shark sightings," mentioning "the growing population of gray seals."
Not everyone appears to be pleased by the changes. In the past several weeks, five adult gray seals were found shot on Cape Cod beaches from Dennis to Chatham. Some local fishermen have expressed concern over the seals' presence, which has decreased the prevalence of certain fish. It remains unclear, however, who shot the seals.
No shark attacks have been reported off of Massachusetts this year, according to Bethan Gillett, a technician at the International Shark Attack File at the Florida Museum of Natural History.
She did indicate there's been a modest rise in attacks nationwide since May, with seven happening that month, seven reported in June, and three occurring in July so far.
"I don't think we are seeing a spike in attacks, though," Gillett told Discovery News. "The attacks are correlated with more people in the water for recreational activities."
One shark victim was a 12-year-old boy who was bitten in the foot by a bull shark off the Texas Gulf coast. The boy has endured several surgeries and requires more, but he is expected to make a full recovery.
"This was very unusual for Texas," Mike Cox, a spokesperson for the Texas Parks and Wildlife Department, told Discovery News. "We haven't had a fatality due to shark attack since 1962, so no one feels this is cause for panic or alarm. You are more likely to be hit by lightning than to be bitten by a shark."
LaCasse pointed out that bull sharks can be particularly tenacious, since they have the highest measured testosterone of any animal. To avoid encountering one, or any shark, he advises, "If you see a seal in the water, you should not be in the water. We're poor swimmers, and when sharks see us thrashing around, they can confuse us for their desired prey."
He also advises not to swim alone in deep water and not to swim at dusk, when visibility is down and shark numbers might be up.
http://www.msnbc.msn.com/id/43797180/ns/technology_and_science-science/t/great-white-sharks-amass-marthas-vineyard/
The sharks make a pilgrimage to this region every year to feed, but a particularly large gray seal population has become an enticing magnet for the large, toothy predators. The presence of the sharks has created a booming tourism business as well as some jitters in the area.
"Gray seals have a lot of blubber and meat, so they are a high efficiency preferred menu item of great white sharks," New England Aquarium spokesperson Tony LaCasse told Discovery News. "Somehow the word is out in the great white world that this is the place to be."
He added, "Humans are not on their menu because we are a completely inefficient meal, since great white sharks are looking for maximum calories per kill."
Federal protection of marine mammals has been in place since 1972, and has led to the recovery of gray seals in the area, which are larger and fattier than Harbor seals that are in the waters off of Cape Cod. LaCasse suspects it took this long for gray seals to build up their population.
When seal numbers were down, the great white sharks mostly fed on dead whale carcasses, called "floaters." LaCasse said just this May, a fisherman went to explore a dead Minke whale near Martha's Vineyard and was surprised by a great white shark that swam out from under the whale "and checked him out.” The fisherman escaped without injuries.
Monomoy Island, where the great whites have been spotted, is an 8-mile spit of sand extending southwest from Cape Cod, and a national wildlife refuge, where access is limited. This has helped to keep people safe from the sharks. A booming tourism industry, with great white sharks as the No. 1 draw, has emerged in nearby Chatham, Mass. Tourism dollars are down by 4 percent in the Cape as a whole, but Chatham has seen a 15 percent uptick, especially now that it's the summer vacation season. LaCasse said during one recent tour, "a great white took a free-swimming seal" in a bloody, violent battle viewed by families riveted to the real life event.
Recent research supports the rise in great white shark numbers off of Cape Cod. A tagging project led by Greg Skomal of the Massachusetts Division of Marine Fisheries (DMF), succeeded in tagging six white sharks, ranging from 10 to 18 feet in length, off the coast of Monomoy Island. The DMF notes there has been a "recent increase in shark sightings," mentioning "the growing population of gray seals."
Not everyone appears to be pleased by the changes. In the past several weeks, five adult gray seals were found shot on Cape Cod beaches from Dennis to Chatham. Some local fishermen have expressed concern over the seals' presence, which has decreased the prevalence of certain fish. It remains unclear, however, who shot the seals.
No shark attacks have been reported off of Massachusetts this year, according to Bethan Gillett, a technician at the International Shark Attack File at the Florida Museum of Natural History.
She did indicate there's been a modest rise in attacks nationwide since May, with seven happening that month, seven reported in June, and three occurring in July so far.
"I don't think we are seeing a spike in attacks, though," Gillett told Discovery News. "The attacks are correlated with more people in the water for recreational activities."
One shark victim was a 12-year-old boy who was bitten in the foot by a bull shark off the Texas Gulf coast. The boy has endured several surgeries and requires more, but he is expected to make a full recovery.
"This was very unusual for Texas," Mike Cox, a spokesperson for the Texas Parks and Wildlife Department, told Discovery News. "We haven't had a fatality due to shark attack since 1962, so no one feels this is cause for panic or alarm. You are more likely to be hit by lightning than to be bitten by a shark."
LaCasse pointed out that bull sharks can be particularly tenacious, since they have the highest measured testosterone of any animal. To avoid encountering one, or any shark, he advises, "If you see a seal in the water, you should not be in the water. We're poor swimmers, and when sharks see us thrashing around, they can confuse us for their desired prey."
He also advises not to swim alone in deep water and not to swim at dusk, when visibility is down and shark numbers might be up.
http://www.msnbc.msn.com/id/43797180/ns/technology_and_science-science/t/great-white-sharks-amass-marthas-vineyard/
Friday, February 11, 2011
Great White Shark Sighting Reported Off La Jolla Coast
Warnings Issued For Swimmers, Surfers, Divers In Area
POSTED: 3:46 pm PST February 10, 2011
SAN DIEGO -- A reported sighting of a small great white shark about 500 yards off the coast of La Jolla Cove Thursday prompted lifeguards to issue precautionary warnings to swimmers, surfers and divers entering the ocean in the area.
Two scuba divers said they saw the marine predator -- a roughly 5-foot-long specimen -- under roughly 30 feet of water about 1:30 p.m., lifeguard Lt. John Everhart said.
Due to the depth and distance from land at which the pair of women spotted the shark, lifeguards did not consider the animal's possible lingering presence in the area an imminent public threat, according to Everhart.
Still, lifeguards warned all entering the water in the area through the afternoon about the reported sighting as a precaution, he said.
http://www.10news.com/news/26825764/detail.html
POSTED: 3:46 pm PST February 10, 2011
SAN DIEGO -- A reported sighting of a small great white shark about 500 yards off the coast of La Jolla Cove Thursday prompted lifeguards to issue precautionary warnings to swimmers, surfers and divers entering the ocean in the area.
Two scuba divers said they saw the marine predator -- a roughly 5-foot-long specimen -- under roughly 30 feet of water about 1:30 p.m., lifeguard Lt. John Everhart said.
Due to the depth and distance from land at which the pair of women spotted the shark, lifeguards did not consider the animal's possible lingering presence in the area an imminent public threat, according to Everhart.
Still, lifeguards warned all entering the water in the area through the afternoon about the reported sighting as a precaution, he said.
http://www.10news.com/news/26825764/detail.html
Thursday, November 18, 2010
Mediterranean sharks are Australian immigrants
Antipodean great whites took a wrong turn on the way to South Africa.
Joseph Milton
The elusive great white sharks of the Mediterranean Sea may be descended from a single small Australian population that lost its bearings while visiting South Africa 450,000 years ago.
The great whites (Carcharodon carcharias) were probably returning to the Antipodes but became trapped after passing through the Straits of Gibraltar, according to a team led by marine biologist Leslie Noble of the University of Aberdeen, UK. The sharks have since made the Mediterranean their home because they reproduced there and, like salmon, the young always return to their birthplace.
Little is known about Mediterranean great whites — sightings are rare and tissue samples even rarer — but Noble and his colleagues teamed up with Turkish researchers to get access to samples from four sharks caught in fishing nets: two from Turkey, one from Tunisia and another from Sicily.
Their research, published today in Proceedings of the Royal Society B1, suggests that a combination of climate change, high sea levels and strong ocean currents around the South African coast could have driven the migrating Australian sharks off-course, up the west coast of Africa and east into the Mediterranean. But because the initial population was small, genetic variability in modern Mediterranean sharks seems to be limited — indicating that a lack of diversity could threaten their future survival. Female sharks from the nearby Atlantic do not seem to be migrating to the region, where they could help to replenish the stagnant gene pool.
Lost at sea
The researchers sequenced an area of the four sharks' mitochondrial DNA — DNA that is passed onto offspring from the mother and encodes proteins from cells' energy factories. The team was then able to compare the genetic code with a bank of sequences derived from great whites in waters of different parts of the world, including South Africa, Australia and the Atlantic.
Noble says the team was surprised to find that the section of DNA sequenced was identical in three of the four Mediterranean sharks, and showed that they were most closely related to Australian great whites. The team had expected to see more affinity with the nearer Atlantic or western Indian Ocean populations.
Great white sharks were once thought of as a coastal species, but research has shown that they migrate long distances in the open ocean — although scientists do not know exactly why. Tagged sharks have been seen travelling between the coasts of South Africa and southern Australia, and the authors suggest that it was probably during one of these excursions that a group took a wrong turn.
The researchers used a molecular dating technique based on the number of differences between the DNA of the Mediterranean and Australian sharks to estimate that the sharks got lost during the Pleistocene epoch, around 450,000 years ago. Noble says that this was an period between ice ages: a time of high sea levels, climate change and, perhaps most importantly, an unusually fast-flowing ocean eddy off the east coast of South Africa called an Agulhas ring — which may explain why the sharks went so far astray.
The warm Agulhas Current flows down the east coast of Africa, but periodically an Agulhas ring carries its waters around the southern tip of the continent and into the Benguela Current off the west coast. "When sharks follow the Agulhas Current, the cooler waters of the Benguela probably alert them to turn east," says Nelson, "but an Agulhas ring is like a warm-water bubble." A group of sharks swimming in one of these bubbles could miss the turning and find the western coast of Africa between it and its desired destination.
The researchers speculate that the sharks then swam north until the Mediterranean basin gave them a chance to head east again. Once in the basin, they may have become trapped by the peninsulas and narrow channels of the Medterranean.
A population in peril
Paulo Prodöhl, an evolutionary geneticist at Queen's University Belfast, UK, says that although the finding "comprises a precious and unique data set, the sample sizes are really too small to draw conclusive inferences". But he admits that because shark samples are so hard to get hold of, "you have to work with what you can get".
"We recognize the sample-size problem," says Noble. "We're trying to get another 50 Mediterranean samples, which could dramatically change our inferences — we're very keen to access museum material."
But, he says, "I don't think it removes the central tenet — that as far as we're aware, a significant proportion of the Mediterranean sharks are Australian in origin."
Noble also hopes that the work will highlight the plight of a potentially fragile shark population surviving in a polluted and over-fished sea. He says that great whites occupy a "pivotal role" in the Mediterranean, and the removal of top predators from other marine ecosystems has been disastrous.
"On the east coast of America, shark eradication has caused an 'ecological cascade'," says Noble. Populations of species on which sharks prey, such as seals and dolphins, have exploded, unbalancing the whole system. "It's been instrumental in helping kill off some of the shellfish," says Noble. "I wouldn't like to speculate on the consequences for the Mediterranean if this population became extinct."
http://www.nature.com/news/2010/101117/full/news.2010.616.html
Joseph Milton
The elusive great white sharks of the Mediterranean Sea may be descended from a single small Australian population that lost its bearings while visiting South Africa 450,000 years ago.
The great whites (Carcharodon carcharias) were probably returning to the Antipodes but became trapped after passing through the Straits of Gibraltar, according to a team led by marine biologist Leslie Noble of the University of Aberdeen, UK. The sharks have since made the Mediterranean their home because they reproduced there and, like salmon, the young always return to their birthplace.
Little is known about Mediterranean great whites — sightings are rare and tissue samples even rarer — but Noble and his colleagues teamed up with Turkish researchers to get access to samples from four sharks caught in fishing nets: two from Turkey, one from Tunisia and another from Sicily.
Their research, published today in Proceedings of the Royal Society B1, suggests that a combination of climate change, high sea levels and strong ocean currents around the South African coast could have driven the migrating Australian sharks off-course, up the west coast of Africa and east into the Mediterranean. But because the initial population was small, genetic variability in modern Mediterranean sharks seems to be limited — indicating that a lack of diversity could threaten their future survival. Female sharks from the nearby Atlantic do not seem to be migrating to the region, where they could help to replenish the stagnant gene pool.
Lost at sea
The researchers sequenced an area of the four sharks' mitochondrial DNA — DNA that is passed onto offspring from the mother and encodes proteins from cells' energy factories. The team was then able to compare the genetic code with a bank of sequences derived from great whites in waters of different parts of the world, including South Africa, Australia and the Atlantic.
Noble says the team was surprised to find that the section of DNA sequenced was identical in three of the four Mediterranean sharks, and showed that they were most closely related to Australian great whites. The team had expected to see more affinity with the nearer Atlantic or western Indian Ocean populations.
Great white sharks were once thought of as a coastal species, but research has shown that they migrate long distances in the open ocean — although scientists do not know exactly why. Tagged sharks have been seen travelling between the coasts of South Africa and southern Australia, and the authors suggest that it was probably during one of these excursions that a group took a wrong turn.
The researchers used a molecular dating technique based on the number of differences between the DNA of the Mediterranean and Australian sharks to estimate that the sharks got lost during the Pleistocene epoch, around 450,000 years ago. Noble says that this was an period between ice ages: a time of high sea levels, climate change and, perhaps most importantly, an unusually fast-flowing ocean eddy off the east coast of South Africa called an Agulhas ring — which may explain why the sharks went so far astray.
The warm Agulhas Current flows down the east coast of Africa, but periodically an Agulhas ring carries its waters around the southern tip of the continent and into the Benguela Current off the west coast. "When sharks follow the Agulhas Current, the cooler waters of the Benguela probably alert them to turn east," says Nelson, "but an Agulhas ring is like a warm-water bubble." A group of sharks swimming in one of these bubbles could miss the turning and find the western coast of Africa between it and its desired destination.
The researchers speculate that the sharks then swam north until the Mediterranean basin gave them a chance to head east again. Once in the basin, they may have become trapped by the peninsulas and narrow channels of the Medterranean.
A population in peril
Paulo Prodöhl, an evolutionary geneticist at Queen's University Belfast, UK, says that although the finding "comprises a precious and unique data set, the sample sizes are really too small to draw conclusive inferences". But he admits that because shark samples are so hard to get hold of, "you have to work with what you can get".
"We recognize the sample-size problem," says Noble. "We're trying to get another 50 Mediterranean samples, which could dramatically change our inferences — we're very keen to access museum material."
But, he says, "I don't think it removes the central tenet — that as far as we're aware, a significant proportion of the Mediterranean sharks are Australian in origin."
Noble also hopes that the work will highlight the plight of a potentially fragile shark population surviving in a polluted and over-fished sea. He says that great whites occupy a "pivotal role" in the Mediterranean, and the removal of top predators from other marine ecosystems has been disastrous.
"On the east coast of America, shark eradication has caused an 'ecological cascade'," says Noble. Populations of species on which sharks prey, such as seals and dolphins, have exploded, unbalancing the whole system. "It's been instrumental in helping kill off some of the shellfish," says Noble. "I wouldn't like to speculate on the consequences for the Mediterranean if this population became extinct."
http://www.nature.com/news/2010/101117/full/news.2010.616.html
Mediterranean sharks are Australian immigrants
Antipodean great whites took a wrong turn on the way to South Africa.
Joseph Milton
The elusive great white sharks of the Mediterranean Sea may be descended from a single small Australian population that lost its bearings while visiting South Africa 450,000 years ago.
The great whites (Carcharodon carcharias) were probably returning to the Antipodes but became trapped after passing through the Straits of Gibraltar, according to a team led by marine biologist Leslie Noble of the University of Aberdeen, UK. The sharks have since made the Mediterranean their home because they reproduced there and, like salmon, the young always return to their birthplace.
Little is known about Mediterranean great whites — sightings are rare and tissue samples even rarer — but Noble and his colleagues teamed up with Turkish researchers to get access to samples from four sharks caught in fishing nets: two from Turkey, one from Tunisia and another from Sicily.
Their research, published today in Proceedings of the Royal Society B1, suggests that a combination of climate change, high sea levels and strong ocean currents around the South African coast could have driven the migrating Australian sharks off-course, up the west coast of Africa and east into the Mediterranean. But because the initial population was small, genetic variability in modern Mediterranean sharks seems to be limited — indicating that a lack of diversity could threaten their future survival. Female sharks from the nearby Atlantic do not seem to be migrating to the region, where they could help to replenish the stagnant gene pool.
Lost at sea
The researchers sequenced an area of the four sharks' mitochondrial DNA — DNA that is passed onto offspring from the mother and encodes proteins from cells' energy factories. The team was then able to compare the genetic code with a bank of sequences derived from great whites in waters of different parts of the world, including South Africa, Australia and the Atlantic.
Noble says the team was surprised to find that the section of DNA sequenced was identical in three of the four Mediterranean sharks, and showed that they were most closely related to Australian great whites. The team had expected to see more affinity with the nearer Atlantic or western Indian Ocean populations.
Great white sharks were once thought of as a coastal species, but research has shown that they migrate long distances in the open ocean — although scientists do not know exactly why. Tagged sharks have been seen travelling between the coasts of South Africa and southern Australia, and the authors suggest that it was probably during one of these excursions that a group took a wrong turn.
The researchers used a molecular dating technique based on the number of differences between the DNA of the Mediterranean and Australian sharks to estimate that the sharks got lost during the Pleistocene epoch, around 450,000 years ago. Noble says that this was an period between ice ages: a time of high sea levels, climate change and, perhaps most importantly, an unusually fast-flowing ocean eddy off the east coast of South Africa called an Agulhas ring — which may explain why the sharks went so far astray.
The warm Agulhas Current flows down the east coast of Africa, but periodically an Agulhas ring carries its waters around the southern tip of the continent and into the Benguela Current off the west coast. "When sharks follow the Agulhas Current, the cooler waters of the Benguela probably alert them to turn east," says Nelson, "but an Agulhas ring is like a warm-water bubble." A group of sharks swimming in one of these bubbles could miss the turning and find the western coast of Africa between it and its desired destination.
The researchers speculate that the sharks then swam north until the Mediterranean basin gave them a chance to head east again. Once in the basin, they may have become trapped by the peninsulas and narrow channels of the Medterranean.
A population in peril
Paulo Prodöhl, an evolutionary geneticist at Queen's University Belfast, UK, says that although the finding "comprises a precious and unique data set, the sample sizes are really too small to draw conclusive inferences". But he admits that because shark samples are so hard to get hold of, "you have to work with what you can get".
"We recognize the sample-size problem," says Noble. "We're trying to get another 50 Mediterranean samples, which could dramatically change our inferences — we're very keen to access museum material."
But, he says, "I don't think it removes the central tenet — that as far as we're aware, a significant proportion of the Mediterranean sharks are Australian in origin."
Noble also hopes that the work will highlight the plight of a potentially fragile shark population surviving in a polluted and over-fished sea. He says that great whites occupy a "pivotal role" in the Mediterranean, and the removal of top predators from other marine ecosystems has been disastrous.
"On the east coast of America, shark eradication has caused an 'ecological cascade'," says Noble. Populations of species on which sharks prey, such as seals and dolphins, have exploded, unbalancing the whole system. "It's been instrumental in helping kill off some of the shellfish," says Noble. "I wouldn't like to speculate on the consequences for the Mediterranean if this population became extinct."
http://www.nature.com/news/2010/101117/full/news.2010.616.html
Joseph Milton
The elusive great white sharks of the Mediterranean Sea may be descended from a single small Australian population that lost its bearings while visiting South Africa 450,000 years ago.
The great whites (Carcharodon carcharias) were probably returning to the Antipodes but became trapped after passing through the Straits of Gibraltar, according to a team led by marine biologist Leslie Noble of the University of Aberdeen, UK. The sharks have since made the Mediterranean their home because they reproduced there and, like salmon, the young always return to their birthplace.
Little is known about Mediterranean great whites — sightings are rare and tissue samples even rarer — but Noble and his colleagues teamed up with Turkish researchers to get access to samples from four sharks caught in fishing nets: two from Turkey, one from Tunisia and another from Sicily.
Their research, published today in Proceedings of the Royal Society B1, suggests that a combination of climate change, high sea levels and strong ocean currents around the South African coast could have driven the migrating Australian sharks off-course, up the west coast of Africa and east into the Mediterranean. But because the initial population was small, genetic variability in modern Mediterranean sharks seems to be limited — indicating that a lack of diversity could threaten their future survival. Female sharks from the nearby Atlantic do not seem to be migrating to the region, where they could help to replenish the stagnant gene pool.
Lost at sea
The researchers sequenced an area of the four sharks' mitochondrial DNA — DNA that is passed onto offspring from the mother and encodes proteins from cells' energy factories. The team was then able to compare the genetic code with a bank of sequences derived from great whites in waters of different parts of the world, including South Africa, Australia and the Atlantic.
Noble says the team was surprised to find that the section of DNA sequenced was identical in three of the four Mediterranean sharks, and showed that they were most closely related to Australian great whites. The team had expected to see more affinity with the nearer Atlantic or western Indian Ocean populations.
Great white sharks were once thought of as a coastal species, but research has shown that they migrate long distances in the open ocean — although scientists do not know exactly why. Tagged sharks have been seen travelling between the coasts of South Africa and southern Australia, and the authors suggest that it was probably during one of these excursions that a group took a wrong turn.
The researchers used a molecular dating technique based on the number of differences between the DNA of the Mediterranean and Australian sharks to estimate that the sharks got lost during the Pleistocene epoch, around 450,000 years ago. Noble says that this was an period between ice ages: a time of high sea levels, climate change and, perhaps most importantly, an unusually fast-flowing ocean eddy off the east coast of South Africa called an Agulhas ring — which may explain why the sharks went so far astray.
The warm Agulhas Current flows down the east coast of Africa, but periodically an Agulhas ring carries its waters around the southern tip of the continent and into the Benguela Current off the west coast. "When sharks follow the Agulhas Current, the cooler waters of the Benguela probably alert them to turn east," says Nelson, "but an Agulhas ring is like a warm-water bubble." A group of sharks swimming in one of these bubbles could miss the turning and find the western coast of Africa between it and its desired destination.
The researchers speculate that the sharks then swam north until the Mediterranean basin gave them a chance to head east again. Once in the basin, they may have become trapped by the peninsulas and narrow channels of the Medterranean.
A population in peril
Paulo Prodöhl, an evolutionary geneticist at Queen's University Belfast, UK, says that although the finding "comprises a precious and unique data set, the sample sizes are really too small to draw conclusive inferences". But he admits that because shark samples are so hard to get hold of, "you have to work with what you can get".
"We recognize the sample-size problem," says Noble. "We're trying to get another 50 Mediterranean samples, which could dramatically change our inferences — we're very keen to access museum material."
But, he says, "I don't think it removes the central tenet — that as far as we're aware, a significant proportion of the Mediterranean sharks are Australian in origin."
Noble also hopes that the work will highlight the plight of a potentially fragile shark population surviving in a polluted and over-fished sea. He says that great whites occupy a "pivotal role" in the Mediterranean, and the removal of top predators from other marine ecosystems has been disastrous.
"On the east coast of America, shark eradication has caused an 'ecological cascade'," says Noble. Populations of species on which sharks prey, such as seals and dolphins, have exploded, unbalancing the whole system. "It's been instrumental in helping kill off some of the shellfish," says Noble. "I wouldn't like to speculate on the consequences for the Mediterranean if this population became extinct."
http://www.nature.com/news/2010/101117/full/news.2010.616.html
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