Great white sharks, much like humans, tend to stick to familiar turf, according to new research. Also like a lot of people, they like to hang out along the coastal waters of California. Sharks tagged with acoustic devices often spent up to 107 days at four key sites along the central and northern California coast where seals and sea lions are abundant: Southeast Farallon Island, Tomales Point, Año Nuevo Island and Point Reyes [LiveScience]. A few of the fearsome predators were tracked as far inland as the Golden Gate Bridge, apparently in search of snacks, say the researchers. The study, the largest and most detailed study of North American great white sharks, provides evidence contrary to the popular notion of great white sharks swimming aimlessly in the ocean.
The sharks under study divided most of their time between three locations: Northern California, Hawaii, and an area that the researchers called the white shark café, a spot in the open ocean about halfway between the Baja Peninsula and the Hawaiian Islands. Exactly what goes on at the café is still unknown–although researchers suspect it may be a hot spot for mating. Lead researcher Salvador Jorgensen explains that male white sharks “converge in a very specific area of the cafe,” Jorgensen said, while female sharks move in and out of the area. “It adds a little more evidence to the argument that this could be an important reproductive area” [Washington Post].
The scientists tracked the snaggly toothed predators between 2000 and 2008 from the Bay Area to San Diego, Hawaii and back as the sharks followed a route that was carried out with surprising precision and under a strict time frame [San Francisco Chronicle]. These great whites have been isolated from other great white sharks near Australia and South Africa for so long that they are now genetically distinct. The study was published in the journal Proceedings of the Royal Society B.
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Image: flickr / hermanusbackpackers
The tiny island nation of Palau has taken a big step to protect the ocean’s endangered sharks, by designating all of its territorial waters a shark sanctuary within which all commercial shark fishing is prohibited. Palau’s president, Johnson Toriboing, announced the plan at a meeting of the UN General Assembly last Friday. Sharks are increasingly under threat as the demand for shark-fin soup—a delicacy in many Asian countries—has risen worldwide. “The need to save the ocean and save sharks far outweighs the need to enjoy bowls of soup,” Toriboing said [National Geographic News].
Palau consists of about 200 small islands in the Pacific Ocean to the east of the Philippines; its expansive marine territory spans 230,000 square miles, an area about the size of Texas. About 130 species of rare sharks either make their homes or pass through these waters, including hammerheads, leopard sharks, and reef sharks, as well as the related stingrays.
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Extinction threatens four more species of deep-sea sharks and rays than a year ago, bringing the total species classified as “threatened” to 20 species, or nearly a third of the world’s 64 species, according to a report (pdf) released today by the International Union for Conservation of Nature. Rays and sharks are already two of the most endangered fish groups, researchers say.
The threat facing pelagic sharks and rays stems largely from overfishing; in many parts of the world, shark meat is considered a delicacy, and some animals become ensnared in fishing nets intended to catch tuna or swordfish. The report also urges governments to halt shark “finning,” the slicing of fins from captured sharks which are then tipped back into the sea to die, which it says is a growing industry providing ingredients for the Asian delicacy, shark fin soup. Although finning bans have been declared in most global waters, little effort is made to enforce them, said the IUCN [Reuters].
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The most menacing predator of the seas has something in common with the most terrifying human predator: A new study has revealed similarities between great white sharks and serial killers. When a great white shark gets hungry, it doesn’t simply head for a crowd of seals and pick off the closest one. Instead, the great white lurks in its favorite hunting spot, waiting for a young and unwary seal to venture into the invisible danger zone. Then, it strikes silently from below.
Researchers used a serial killer profiling method to figure out just how the fearsome ocean predator hunts, something that’s been hard to observe beneath the surface. “There’s some strategy going on,” said study co-author Neil Hammerschlag…. “It’s more than sharks lurking at the water waiting to go after them” [AP].
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Birds and vacationing humans aren’t the only animals to migrate south for the cold months of winter. It turns out that basking sharks do, too.
They are the ocean’s second largest fish, and live in temperate waters from late spring until early fall. But then they disappear, and until now scientists have only been able to guess where they go–some have even suggested that the sharks hibernate on the ocean floor. To find the real answer, the team tagged 25 basking sharks off the coast of Cape Cod and tracked them as they made their wintertime trip. The researchers found that the sharks headed south [to the Caribbean], some going as far as Brazil [Science News].
The basking shark is a benign behemoth. It swims at about three miles per hour with its four-foot-wide mouth gaping open, filtering through almost 500,000 gallons of water every hour for its plankton sustenance [Wired]. They can grow to 35 feet or longer, but aside from knowing the sharks spend most of their time in temperate waters, scientists have been mystified by these fish for years: no one has ever examined a newborn basking shark. No one has seen a pregnant female. No one knows where the animals give birth [Discovery News].
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Using boat, tags, nets, and submarines, marine biologists from 82 nations have been canvassing the oceans for the first Census of Marine Life, an ambitious effort to get a rough tally of all the creatures in the world’s oceans. The 10-year project is expected to conclude in 2010, and researchers say the broad survey will help them observe changes to marine ecosystems. Says co-senior scientist Ron O’Dor: “We are moving into this period of global warming, which is resulting in the acidification of the oceans, melting of the polar ice cap. We can use the first census as a benchmark to see what happens in the oceans over the next decade or more” [BBC News].
Although the project still has two years to go, researchers have already made a host of startling discoveries, many of which will be discussed this week at the World Conference on Marine Biodiversity in Valencia, Spain. In one study, researchers conducted a genetic analysis of deep sea octopuses from around the world, and determined that most descended from a common ancestor species that still lives near Antarctica. Researchers believe that octopuses started migrating to new ocean basins more than 30 million years ago when, as Antarctica cooled and a large icesheet grew, nature created a “thermohaline expressway,” a northbound flow of tasty frigid water with high salt and oxygen content. Isolated in new habitat conditions, many different species evolved; some octopuses, for example, losing their defensive ink sacs — pointless at perpetually dark depths [LiveScience].
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A female blacktip shark in a Virginia aquarium got pregnant despite the fact that no male blacktip sharks shared her tank in her eight years of residency, researchers say. This is the second documented case of asexual reproduction, or parthenogenesis, among sharks; the first example of a shark “virgin birth” occurred with a hammerhead shark in a Nebraska zoo. The new findings suggest that the previous event wasn’t a marine miracle. “This first case was no fluke,” Demian Chapman, a shark scientist and lead author of the second study, said in a statement. “It is quite possible that this is something female sharks of many species can do on occasion” [AP].
Now scientists are debating whether asexual reproduction is a backup method for female sharks that can’t find a mate, or whether the pregnancy was a developmental aberration that occurs from time to time. Chapman argues for the first camp: “The reason this has happened in captivity isn’t because there’s a change in their reproductive biology,” he explains. “It is more likely to happen if female sharks aren’t having enough dates,” he says. “These females did it because they were in captivity and ovulating” [Science News].
But others say that since the shark didn’t produce a normal litter of four to six pups, the pregnancy could have been an anomaly. “The fact that only one shark embryo was formed may suggest that this is more a case of an egg developmental aberration rather than a physiological response to the lack of a mate,” said [shark expert Robert] Hueter [National Geographic News].
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An extinct ancestor of the great white shark had a powerful bite that wouldn’t just put Jaws to shame, according to a new fossil analysis by Australian researchers. The colossal force of Carcharodon megalodon – also known as Big Tooth – made even Tyrannosaurus rex look puny [Telegraph].
In the study, to be published in an upcoming issue of the Journal of Zoology [subscription required], researchers took CT scans of both the skulls of great white sharks and those of the prehistoric megalodon, who swam the oceans about a million and a half years ago. They made computer models of the skulls, and then ran an analysis on the models that engineers use to determine how machinery holds up under stress.
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For a big, lumbering creature, it sure is mysterious. Marine biologists don’t know much about the massive whale shark, which is considered the biggest fish on the planet. They don’t know how many there are or whether they are migratory, and its reproductive habits are obscure. There are even disputes about its size but it can grow reputedly to 60 feet long and weigh as much as 40 tonnes [Telegraph].
However, one thing researchers thought they knew was that whale sharks aren’t the speediest fish in the sea; in all previous sightings, the behemoths have always been cruising slowly just beneath the ocean’s surface. Now, after a couple of enterprising researchers clipped electronic tags to wild whale sharks near western Australia, biologists have realized that deep below the surface the creatures dive at great speeds, and that they use the same principles as a diving hawk. “It is like the way a bird dives – but, in this case, a bird as large as a bus,” said Professor Rory Wilson, who has tracked the movements of the threatened species [Daily Mail].
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It’s not all about the cute fuzzy critters — we’ve got to save the toothy, menacing, bloodthirsty endangered species, too. That’s the message from a new study, which examined shark populations in the Mediterranean and found a lot to be alarmed about. Numbers of some species have fallen 97 percent over the last two hundred years due largely to overfishing, and researchers say that because sharks have been “much maligned,” no one seems to care.
[Lead author Francesco] Ferretti, a researcher at the Biology Department of Dalhousie University in Nova Scotia, said that Steven Spielberg’s 1975 film Jaws had given a misleading impression of sharks. “Spielberg has a lot to answer for,” he said. “In reality you have about as much chance of being eaten by a shark as you have of winning the lottery twice” [Times Online].
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