Feeds:
Posts
Comments

Archive for the ‘sharks’ Category

great hammer beaufort north carolina

This hammerhead, which I think is a great hammerhead, was killed in the harbor at Beaufort, North Carolina, a place that was once frequented by both Blackbeard and yours truly.

This shark is depicted in an article entitled “What Sharks Really Eat” in Natural History in 1921. The article explains what normally has been found in the stomachs of dead sharks, and it’s an obvious attempt to convince people that sharks aren’t that dangerous to people.

Yes. Scientists have been making those claims for that long!

Read Full Post »

great white nice doggy

Nice doggy!  

As it is currently construed, the genus Canis includes certain dog-like species, including the dog/dingo/wolf species, the coyote, the Ethiopian wolf, and the jackals. However, recent genomic analysis suggests that this genus is paraphyletic, and it is in need of revision. In order to make Canis monophyletic, one wold have to include the dhole and African wild dog within the genus or create a genus for the side-striped and black-backed jackals.

But as messed up as the genus Canis is now, just imagine what it was like when there was a Canis carcharias.

This name is the old scientific name for the great white shark. “Canis” means dog in Latin, and “carcharis” means sharp and jagged in Greek.

It was never meant to reflect evolutionary relationships between dogs and sharks. Instead, it was just simple common scientific name that was given to this shark. Some early naturalists even used it as the generic name for all sharks, but my sources show that it almost always referred to the great white.

Classifying animals according to their evolutionary relationships is a very new development in science. Before that, animals were given scientific names based upon the whim of the classifier.

After all, before Buffon and Darwin, it was just assumed that all these creatures were divinely created and calling a shark a “sea dog” or “sea hound” made as much sense as using the term Canis carcharias to classify it.

The first person to use the scientific name Canis carcharias was Guillaume Rondelet, a professor of medicine at the University of Montpellier in southern France in sixteenth century.  Rondelet is considered the father of modern ichthyology, for he was the first to describe fishes and other marine creatures using clearly defined anatomical principles in his Libri de piscibus marinis in quibus verae piscium effigies expressae sunt (1556).  In the text, he describes several massive great whites, which the French and Italians called “lamia,” that were captured in Mediterranean. It’s from him that we get the apocryphal story of a great white that was capture with a full suit of armor in its stomach. These sharks were once quite common throughout the Mediterranean, and they were a very real problem for mariners and swimmers in that region. The reason why the French and Italians called them lamia is in reference to a child devouring sea monster in Greek mythology, and they were certainly very well aware of them.

Rondelet tried to describe this shark as something other than a great hulking sea monster. He tried place it as a naturally defined entity, and in this he did science a great service.

However, he lived before Linnaeus, so he didn’t use the Linnaean classification sytem. Canis was not the genus of the shark, and carcharias was not its species name.

It was just a name he divined, and unfortunately, because he was the first to do this, this became the scientific name used for the species for centuries afterward. In the early nineteenth century. Canis carcharias was still very commonly used to refer to great white sharks.

If one performs a simple search in Google Books for the term “Canis carcharias,” one will find any number of commentaries on great white sharks. However, Linnaeus himself called the species “Squalus carcharias” and dropped any reference  to dogs in the name.

And by the end of the nineteenth century, this name had finally fallen from favor.

Richard Lydekker describes “Rondeleti’s shark” in his The Royal Natural History: Fishes and Reptiles (1896.) The sizes are somewhat exaggerated:

The most formidable of all the existing members of the group is the gigantic Rondeleti’s shark (Carcharodon rondeletii), distinguished from the porbeagles by the great size of the broadly triangular teeth, which have strongly serrated edges, and may possess basal cusps. The existing species, which is a purely pelagic creature ranging over all the warmer seas, is known to attain a length of 40 feet, one of the teeth of a specimen of 36 feet in length measuring 2 inches along the edge of the crown, and 1 3/4 inches across the base. Similar teeth are found in the Crag deposits of Suffolk, and are referred to the existing species; but from these same beds, and also from the bottom of the Pacific, between Polynesia and Australia, there are obtained other teeth of much larger dimensions, some of them measuring upwards of 5 inches along the edge and 4 inches in basal depth. These teeth evidently indicate sharks beside which the existing form is a comparative dwarf; and it is not a little remarkable that the specimens dredged from the bed of the Pacific indicate that these giants must in all probability have survived to a comparatively recent date. Observations are still required as to the mode of life and breeding-habits of Rondeleti’s shark. Two other species of large sharks constitute the genus Odontaspis. With teeth almost indistinguishable from those of the porbeagles, these species differ by the second dorsal and anal fins being nearly as large as the first dorsal, and the absence of a pit at the root of the caudal fin, and of a keel on the sides of the tail (pg. 526).

In Lydekker’s time, it was now more acceptable to classify things using Linnaean taxonomy, and he was also trying to place this shark with its closest relatives. The great white is a giant mackerel shark, and he correctly placed it with the porbeagle, a type of shark that is actually quite common in British waters. (I was always told that porbeagle is a portmanteau between the words porpoise and beagle, another canine reference in shark nomenclature. However, other etymologies have been suggested.)

Further, Lydekker was using the new scientific name for the species that had been given to it by the Scottish zoologist Sir Andrew Smith, who had encountered them in his years as a naturalist in the Cape Colony. South Africa  is still a major stronghold for great white sharks, and they likely were more common in the 1820’s and 1830’s when Smith was living there.

The genus name  “Carcharodon” means jagged tooth, and the species name rondeletiirefers to Rondelet, who was the first to systematically describe the species.

However, Rondelet called the species Canis carcharias, so following the scientific tradition of allowing the first discoverer to name the species, we now call the great white Carcharodon carcharias.

It matter not that Rodelet wasn’t trying to classify the great white in the way we do now.

In fact, we really don’t use the same Linnaen system anymore.

We now used cladistic classification, which is why we’re now arguing about how to classify African wild dogs and black-backed jackals in the genus Canis and no serious person would try to call a great white shark a dog.

Great whites are sharks we’ve known for quite some time. They’ve likely attacked humans for thousands of years before we ever had any idea of what they were.

Ancient man just thought of them as evil sea monsters.

More advanced civilizations thought of them as great sea dogs.

And now we know them as amazingly derived mackerel sharks whose predatory prowess is rivaled by few other ocean creatures.

Ranging throughout the world’s oceans, the great white has been one of the most successful species of shark on the planet. Its ability to generate its own body heat has mean that it can travel into quite cold seas in search of marine mammal prey, and they have even been found 4,000 feet below the ocean’s surface.

But now the species is vulnerable.

We’ve killed them by the score. We have thought that if we killed off these sea demons, the oceans would be safe for everyone. Maybe even safe for democracy.

But the truth is the great white does play a vital role as one of the ocean’s top predators.

Without them, the ecosystem falls out of balance, and certain species begin to overpopulate.

We are only just now beginning to realize how important this giant sea dog actually is to maintaining the health of the oceans.

And we may have figured this out before it’s too late.

 

 

 

 

 

 

Read Full Post »

From the BBC:

Lemon sharks have the ability to learn from each other’s behaviour, scientists have found.

The team compared the performance of inexperienced juvenile sharks working with both trained and untrained partners.

The results showed that sharks working with trained partners could complete tasks more quickly and successfully.

The study is thought to be the first to demonstrate social learning in any cartilaginous fish.

“I think it’s a really cool finding,” said lead author Dr Tristan Guttridge, director of the Bimini Biological Field Station in the Bahamas, whose paper was published in the Journal of Animal Cognition.

The results are a significant breakthrough, according to Dr Guttridge.

“It’s a pretty exciting finding that these little lemon sharks are able to pick up social cues from each other,” he said.

The evidence came from a task-based experiment with juvenile sharks conducted in an underwater pen.

The pen contained an “indicator zone” which functioned as the start area. In the other corner was a “target zone” in which there was a black and white marker that could be covered or exposed by the scientists.

When the sharks swam into the indicator zone, the target was exposed.

By swimming into the target zone and bumping the black and white target they earned a piece of barracuda, which was lowered into the pool.

One group of sharks, the “trained demonstrators” was trained in this task until they could complete it roughly six times every minute. Another group, the “sham demonstrators”, was left untrained.

Members of each group were then paired up with “naive”, untrained sharks and the pairs were introduced to the pool, observed and filmed.

“You can see the shark that’s been with the demonstrator, how interested he is in the particular zones, moving between them,” said Dr Guttridge of the video footage.

“It’s really quite obvious that they’re picking up social cues from the other individual and the excited behaviour of the demonstrator is getting the other guy interested as well.”

The study then isolated those sharks that had observed the demonstrators to see how they performed on their own.

The juveniles that had been paired with “demonstrator sharks” completed a greater number of trials more quickly than those with untrained partners.

Wow.

So at least with lemon sharks, there is quite a bit of social learning going on.

 

 

Read Full Post »

Shark Week

My sister caught an Atlantic sharpnose shark (Rhizoprionodon terraenovae) while at Myrtle Beach, South Carolina, this week.  Casey and Zech, her fiancé, are displaying the trophy. She also caught an Atlantic croaker while on this fishing trip.

Read Full Post »

Well, there was a great white attack in Massachusetts on July 30.

It was just confirmed yesterday:

The Massachusetts Division of Marine Fisheries (DMF) confirmed on Tuesday that the shark that bit a Colorado man swimming off a Cape Cod beach on July 30 was a white shark. It marks the first confirmed white shark attack in Massachusetts in 76 years.

“Working with George Burgess, the curator of the International Shark Attack File, officials from the Massachusetts Division of Marine Fisheries have determined that the injuries sustained by Chris Myers off Ballston Beach, Truro on July 30 can be attributed to a great white shark,” said Reginald Zimmerman, a spokesman for the Executive Office of Energy and Environmental Affairs. “This conclusion was reached after examination of the injuries and testimony from Myers.”

Over the last several years white shark sightings have increased off the coast of Massachusetts. DMF researchers have been monitoring and tagging white sharks since 2009.

Cape Cod is home to a relatively large colony of gray seals, which the sharks are definitely hunting.

This part of the country has had very few shark attacks.

Shark attacks aren’t that common anyway, but on the Atlantic Coast, they are virtually unheard of north of Cape Hatteras.

There have been fatal great white attacks in Massachusetts history.

My personal favorite story is the one where a great white took a man off a dory in 1830.

Joseph Blaney rowed a small dory off the main ship and began fishing.

And this his fellow fishermen saw a big fish jump onto the dory.

He fell into the water, and all that was recovered was his hat.

Blaney’s family later went fishing for sharks at that same location in hopes of catching the man-eater.

They caught two great whites, one of which was too big to haul into shore.

Great whites still rarely attack people.

So I don’t think they should call in this guy just yet:

 

Read Full Post »

This was the first time this guy ever kayaked!

MSNBC reports:

A first-time kayaker had a close encounter with a great white shark off the coast of Massachusetts over the weekend.

Sunbathers first spotted the shark following two kayakers on Saturday afternoon off Nauset Beach, the Cape Cod Times reported, and yelled to the men offshore.

One of the kayakers saw the shark and quickly paddled in, while it took the other one, Walter Szulc Jr., of Manchester, N.H., a little while longer to notice the dorsal fin just feet away from him.

“There were hundreds of people on the beach, and they were all at the edge, yelling paddle paddle, paddle!” Dave Alexander told the NBC News affiliate in Boston, WHDH.com.

Szulc said when he looked behind him, the shark “was pretty much right there.”

“It was good-sized, it had a fin sticking out, so I just turned and paddled,” he told WHDH.com. It was the first time Szulc had kayaked.

Since June 30, three sharks have been seen plying the waters off Cape Cod for food, the Cape Cod Times reported. The large number of seals in the area is believed to be drawing the sharks.

Orleans Harbormaster Dawson Farber said he and his team went out in a boat to confirm the sighting – he noted the shark was an estimated 12 to 14 feet long — and they had all bathers get out of the water. The beach was also closed.

“Everyone was very relaxed and the shark put on quite a show moving back and forth out in front of the beach, but it was done in a very orderly fashion,” Farber told ABC News.

Witness Debbie Sutton said Szulc “started booking it.”

“You could see the darkness of it,” she told WHDH.com. “It was longer than the kayak … it was crazy big.”

Not all beachgoers were scared by the great white. Some even got into the water at the beach later in the day.

“Everyone wanted to see it,” Karen O’Connell of Medfield told the Cape Cod Times. “There were people running toward it.”

The last shark attack on a human in the area was in 1936, when a man was killed swimming near Mattapoisett, the newspaper reported.

Great white sharks come to New England for a very simple reason:

The New England gray seal population is continuing to grow.  And we all know that great whites are major predators of marine mammals.

Gray seals have made a comeback in the northwestern Atlantic. Both Massachusetts and Maine had bounties on gray seals, and they were heavily persecuted in Atlantic Canada for transmitting the cod worm.

The United States has very strict regulations for protecting seal and sea lions. The Marine Mammal Protection Act of 1972 has allowed seals and sea lions to thrive in our waters.

Of course, as they have been able to thrive, so may their predators.

Great whites are currently protected in US waters.

So people are going to be swimming in water that contains a predator and prey dynamic of two protected species.

It’s actually somewhat amazing that these sharks haven’t attacked anyone since 1936.

The potential is there.

It just hasn’t happened yet.

Read Full Post »

From Sea and Land by J. W. Buel, 1889

Read Full Post »

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 :

Source.

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.”

Read Full Post »

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.

Read Full Post »

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.

 

 

 

Read Full Post »

Older Posts »

%d bloggers like this: