Archive for the ‘sharks’ Category

A baby salmon shark chases baitfish too close to the shore. It gets stranded. (I can’t see claspers, so I think it’s a female).

Three rescue attempts later, and it finally makes it into the water :


Salmon sharks are closely related to great whites, porbeagles, and the two species of mako.

Salmon sharks are found on both sides of the North Pacific.

Ecologically, they are more like the Pacific version of the porbeagle, which some call a “mackerel shark.”

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From Wired.com:

In the stomachs of tiger sharks in the Gulf of Mexico, researchers are finding something unusual: land-faring migratory birds.

Sharks are known to eat seafaring birds, but land birds such as woodpeckers, meadowlarks, swallows and tanagers are unexpected.

“We’re the first to look this exhaustively at the diet of tiger sharks, as far as I know, and this certainly seems surprising,” said fisheries ecologist Marcus Drymon, leader of an ongoing tiger shark diet study at the Dauphin Island Sea Lab in Alabama.

The American Bird Conservancy thinks the research suggests oil platforms are to blame for dropping migratory birds into Gulf waters. Night-flying birds are known to get trapped in bright light sources, including offshore oil platforms and the 9/11 memorial lights. More than 6,000 illuminated platforms that pepper the Gulf could become giant nighttime bird lures, causing birds to circle in confusion until they’re exhausted, drop into the water and become shark food.

“Unfortunately, we don’t have good baseline data to know that,” Drymon said. “We don’t know if migratory birds are normal things for them to eat or not. There’s no data on tiger shark diet from 100 or 50 or even 30 years ago.”

Migratory land birds in the U.S. typically overwinter in South America and return in the spring or summer. Each leg of the migration is a non-stop flight covering hundreds or even thousands of miles. Threats range from storms and airborne predators to exhaustion and malnutrition.

The birds stay on course in part by using moonlight and starlight to calibrate internal compasses. Human light pollution can interfere with that ancient system, and poses an evolutionarily unique challenge that researchers have just started to study.

These are all interesting theories, but there are a few possible problems with interpreting these facts in this fashion.

First of all, I don’t know how clearly we know that birds use the moon and starlight to migrate.  It has been one of the theories postulated, but I don’t think we have any kind of definitive evidence of how birds migrate.

Tiger sharks are called the garbage men of the sea for a very simple reason:  they will eat anything.  The ones around Hawaii have been found with mongooses in their stomachs.  The small Indian mongoose that was introduced from Jamaica is not an aquatic animal, but whenever there are heavy rains in Hawaii, some mongooses get flushed out to see, where the tiger sharks pick them off.

And anyone who has ever seen Jaws can remember the scene where Hooper dissects a large tiger shark that had been caught by a mob of bounty fishermen.  When Hooper opens up the tiger shark’s stomach, he finds a Louisiana license plate.

The discovery of what appear to be rather large numbers of land-based migratory birds in the stomachs of tiger sharks is really interesting, and it does raise an interesting hypothesis.

Are oil rigs causing the problem with the collapse of so many migratory birds?

Counting the number of birds in tiger shark stomachs is not a very good measure for the reasons I’ve just described.

Further, we don’t know how many land-based birds are normally found inside tiger sharks.

To do the experiment, we’d have to get some analysis from tiger sharks that are found in seas without oil rigs and that exist along major migratory routes for birds.

I don’t know of any regions that meet those criteria.

So it’s an interesting hypothesis, but it is going to require a lot more study to be in any way definitive.

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From the Washington Post:

Scientists have identified the first-ever hybrid shark off the coast of Australia, a discovery that suggests some shark species may respond to changing ocean conditions by interbreeding with one another.

A team of 10 Australian researchers identified multiple generations of sharks that arose from mating between the common blacktip shark (Carcharhinus limbatus) and the Australian blacktip (Carcharhinus tilstoni), which is smaller and lives in warmer waters than its global counterpart.

“To find a wild hybrid animal is unusual,” [This is not true.] the scientists wrote in the journal Conservation Genetics. “To find 57 hybrids along 2,000 km [1,240 miles] of coastline is unprecedented.”

James Cook University professor Colin Simpfendorfer, one of the paper’s co-authors, emphasized in an e-mail that he and his colleagues “don’t know what is causing these species to be mating together.” They are investigating factors including the two species’ close relationship, fishing pressure and climate change.

Australian blacktips confine themselves to tropical waters, which end around Brisbane, while the hybrid sharks swam more than 1,000 miles south to cooler areas around Sydney. Simpfendorfer, who directs the university’s Centre of Sustainable Tropical Fisheries and Aquaculture, said this may suggest the hybrid species has an evolutionary advantage as the climate changes.

As a result, he wrote, “We are now seeing individuals carrying the more tropical species genes in more southerly areas. In a changing climate, this hybridization may therefore allow these species to better adapt to different conditions.”

The researchers — who had been working on a government-funded study of the structure of shark populations along Australia’s northeast coast — first realized something unusual was going on when they found fish whose genetic analysis showed they were one kind of blacktip but their physical characteristics, particularly the number of vertebrae they had, were those of another. Shark scientists often use vertebrae counts to distinguish among species.

The team also found that several sharks that genetically identified as Australian blacktips were longer than the maximum length typically found for the species. Australian blacktips reach 5.2 feet; common blacktips in that part of the world reach 6.6 feet.

Demian Chapman, assistant director of science of Stony Brook University’s Institute for Ocean Conservation Science, said the idea that sharks can interbreed is “something a lot of shark biologists thought could happen but now we have evidence, and it’s fantastic evidence.”

He added, however, that the fact that these two species were so closely related made it easier for them to mate than wildly-divergent ones.

“It doesn’t mean we’re going to see great-white-tiger sharks anytime soon, or bull-Greenland sharks,” he said. “If any species was going to hybridize, it was going to be this pair.”

Chapman, who first documented in 2008 that some female sharks can reproduce without having intercourse, said this latest discovery suggests “there’s yet another path to reproduction that these species can do. It just reinforces that sharks can do it all when it comes to reproduction.”

Hybridization with related species happens much more often in the wild than scientists have ever realized.

Hybridization in the wild is pretty common with dogs in the genus Canis and the cats in the genus Lynx.  Various waterfowl species regularly hybridize in the wild.

However, hybridization with sharks has never been seen before.

The authors of this study think that these hybrid sharks are the result of some problems with climate change and overfishing.

However, one has to realize that species are never static things.

Purportedly distinct species have occasionally hybridized, and this hybridization may have conferred upon the hybrids advantages.

There are some studies that have suggested that the hybridization between modern humans and Neanderthals (and possibly Denisovans)  may have given us unique MHC genes that allowed us to colonize Eurasia.

With these sharks, the cold tolerance of the common blacktip has been conferred onto the hybrid, and because these hybrids are likely fertile, the blacktip species will be able to colonize the coast of southern Australia.

We can think of this as the result of a species in trouble, which is certainly a possibility.

Or we can think of this as another evolutionary offshoot. Hybridization can be an opportunity, not a loss.




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Wait until the end.  You know it’s gonna happen, and it does.


He doesn’t know how lucky he is.

Would I try to hand-feed a hammerhead from the boat?

Not on your life!

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More about him here.

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From the Sydney Morning Herald:

A British man has been mauled by a shark while swimming in South Africa, authorities said.

The 42-year-old man is fighting for his life after the attack by a great white at Fish Hoek beach in Cape Town.

Reports said the man, who is believed to live in the city, was rescued by a bystander after he ignored shark warnings to go swimming.

National Sea Rescue Institute (NSRI) spokesman Craig Lambinon told the South African Press Association (Sapa): “It appears he was rescued from the water by a bystander who left the scene before we could identify him.

“On arrival, a 42-year-old man was found on the shore suffering complete amputation of his right leg, above the knee, and partial amputation of his left leg, below the knee.”

Mr Lambinon said the victim was believed to live in the suburb of Plumstead.

He was stabilised at the scene and then airlifted to Constantiaberg Medi-Clinic in a critical condition.

Mr Lambinon said: “The man was conscious when paramedics attended to him on the beach, but was sedated on-scene by paramedics in their efforts to stabilise the patient.”

The city of Cape Town told Sapa that, when the man entered the water, the beach was still closed. A shark flag, indicating the presence of a great white, was flying.

A shark spotter stationed on the beach was warned by a spotter on the mountain that someone had entered the water.


The shark spotters tell the authorities to warn everyone.

Everyone gets out of the water.

This man goes in.

Shark eats his legs.

Maybe he thought they were like dolphins.





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The documentary is in German, but I don’t know where this was filmed.

Tiger sharks and blue whales are both wide ranging species.

This is not a big blue whale. It’s only about 60 feet long!

Nature isn’t always so nice.

This would be like a human being eaten alive by pack of weasels.

Not a great way to go.


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