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Posts Tagged ‘sharks’

So says a new genetic study that examined samples from 4,283 individual sharks.  It found 574 species, and 79 of these are likely new species.

These new species are actually cryptic species.  A cryptic species is one that is suddenly discovered from a population of what appear to a species already known to science, or it can happen when two populations that have been classified as the same species turn out to have quite a bit more genetic diversity than was previously thought.

For example:

For example, Naylor’s work suggests that the endangered scalloped hammerhead (Sphyrna lewini) is actually two separate species. “Scalloped hammerheads in general have taken a huge hit, so it may be even worse than has been documented if there’s more than one species out there,” he says.

Now, this is really an interesting find.

I’ve often wondered if our traditional classification of shark species would withstand molecular genetic analysis.

It doesn’t look like it will.

For example, I’ve often questioned whether all the sand tiger sharks (Carcharias taurus) are all really of the same species. These sharks are found only near coasts, and they are found in quite isolated populations in different parts of the world.

I bet there isn’t much gene flow between those populations– if any– and they likely have been reproductively isolated for a fairly long time.

Sharks have been around for a long time, and even modern species have had more than enough time to experience multiple divergences from a common ancestor.

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Source.

The tiger shark is one of the species that does occasionally attack people.

But this footage shows them to have a certain amount of grace and beauty that one might not suspect from a creature known as the “garbage man of the sea.”

They tend to eat just about anything– as you may remember from Jaws. In that film, the amateur bounty fishermen catch a big tiger shark and claim it as the beast that has been terrorizing Amity Island. Hooper, the marine biologist played by Richard Dreyfuss, demands that he cut open the shark to see what it has been eating. He finds a Louisiana license plate inside.

One would expect an animal that eats things like license plates to be very dull and brutish.

But when you look into the eyes of these tiger sharks, you see something one would never expect to see in a fish.

It’s a kind of glimmer of intelligence.  It’s not quite mammalian, but it’s  more of a spark than one would find in a largemouth bass or a bluegill.

Tiger sharks are one of the species targeted by shark finners, and in North American waters, they have been heavily persecuted.

I remember seeing one when I was a small boy. It has been captured by a charter fishing boat that had seen the shark devouring a loggerhead sea turtle. (Tiger sharks are excellent sea turtle predators. Sea turtles are one of their favorite prey items.)

The boat’s captain had seen the shark eating the turtle, but he decided to not to catch it.

They didn’t have a very good day out pursuing billfish, so on their way back, they cast lines for the shark. They snagged it, and after a struggle, they hauled it in.

They had not caught a great blue marlin that day.

The fishermen had been failures.

But now they had tangled with a murderous beast of prey.

They had vanquished the great sea monster, and now they could come back to port as heroes.

Knowing that such a creature could live in the water in which people swam scared me a bit. When I was younger, I used to have dreams about being attacked by a big shark that grabbed me with its jaws in the surf.

Even today, I won’t swim in murky ocean water off the coast. I don’t mind swimming in clear ocean water– one of my favorite days was when I went snorkeling in Hawaii.

But I won’t get in the water if I can’t see to the bottom.

However, as I look at the spark in the eyes of these tiger sharks, they seem less scary, less menacing.  I feel for them in the way I have felt for wolves and other terrestrial carnivores.

Just as the land needs tigers and wolves, the ocean will need tiger sharks.

That tiger sharks sometimes attack people should not given us license to exterminate them.

Look into those eyes, and the being that is a tiger shark is revealed.

A commonality is there.

I just didn’t expect it.

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From Science Daily:

Researchers have found antibiotic-resistant bacteria in seven species of sharks and redfish captured in waters off Belize, Florida, Louisiana and Massachusetts. Most of these wild, free-swimming fish harbored several drug-resistant bacterial strains.

The study, published in the Journal of Zoo and Wildlife Medicine, found antibiotic-resistant bacteria in every fish species sampled.

The researchers also found multidrug-resistant bacteria in fish at nearly all of the study sites, said Mark Mitchell, a professor of veterinary clinical medicine at the University of Illinois and a senior author of the paper.

“Ultimately the idea of this study was to see if there were organisms out there that had exposures or resistance patterns to antibiotics that we might not expect,” Mitchell said. “We found that there was resistance to antibiotics that these fish shouldn’t be exposed to.”

Among the animals sampled, nurse sharks in Belize and in the Florida Keys had the highest occurrence of antibiotic-resistant bacteria. These sharks feed on crustaceans, small fish and other animals living in shallow waters close to shore.

Random mutations may account for drug-resistant bacteria in marine environments, Mitchell said, but there is a lot of evidence for a human origin.

“The shark population in Belize, for example, is a big tourist area, so there are people in the water right there,” he said. “The sampling site is not far from a sewage plant, and so all those exposures we think are playing a role.”

Sewage also is a problem in the Atlantic coastal waters of the United States, he said. Previous studies have shown that sewage outflows can leak antibiotic-resistant bacteria into the environment.

In the new study, the researchers looked for and found bacterial resistance to 13 antibacterial drugs in the fish. Patterns of resistance varied among the sites.

Bacteria from sharks off Martha’s Vineyard in Massachusetts and in offshore Louisiana were resistant to the fewest number of antibiotics, while sharks in the Florida Keys and Belize harbored bacteria that were resistant to amikacin, ceftazidime, chloramphenicol, ciprofloxacin, doxycycline, penicillin, piperacillin, sulfamethoxazole and ticarcillin.

Redfish in the Louisiana offshore site hosted more varieties of drug-resistance than sharks in the same waters. This may reflect differences in their age (the redfish were more mature than the sharks), feeding or migratory habits, Mitchell said.

While the presence of antibiotic-resistant bacteria in sharks and other fish does not necessarily harm them, Mitchell said, the findings point to a growing problem for human health.

“There are estimates of over 100,000 deaths from infections in hospitals per year, many of them from antibiotic-resistant organisms,” Mitchell said. “And we’re creating even more of these organisms out in the environment. … Unfortunately, as these things collect, there’s probably a threshold at some point where there’s going to be a spillover and it will start to affect us as a species.”

People do eat sharks and redfish, Mitchell said, and now these fish represent a potential new route of exposure to drug-resistant bacteria. Sharks and redfish also are predators, and so may function as sentinels for human health.

“Some people might say, well, a bull shark in offshore Louisiana doesn’t really have an influence on my health,” Mitchell said. “But these fish eat what we eat. We’re sharing the same food sources. There should be a concern for us as well.”

This study was the thesis for first author Jason Blackburn, a former master’s student at Louisiana State University now on the faculty at the University of Florida. The team included researchers from LSU, the University of Florida, the U. of I. and the University of Southern California.

This means that fish could be a source for drug-resistant bacteria, which is not a very good thing.

Of course, redfish from the Gulf are probably a thing of the past.

If that’s any consolation.

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Sandbar shark

I’ve been spending a few days at my relatives’ beach house in Myrtle Beach, South Carolina– a place I call “West Virginia’s coast,” simply because so many people from West Virginia come here on holidays.

Now, I am far from the typical beachgoer.

I don’t like spending hours sitting in the sun. I’m very fair-skinned, and I have to put on very high-powered sunscreen. And I actually don’t like swimming in salt water.

But I am a nature nut.

And I love to go on long nature walks.

Here, I have to walk three or four miles before I get beyond all the resorts and into the open beach, where I can see all sorts of little shore birds. I have yet to see any dolphins or porpoises here, but I know that if I’m going to see any of those, it will be away from the crowded beaches. That’s why I’m willing to take such long journeys away from the beach house.

I did, however, see something quite amazing this week.

On the Outer Banks of North Carolina,  I have seen many dolphins and porpoises, and from the shore, I’ve seen a few blacktip sharks and bonnetheads. I certainly wasn’t expecting to see those animals. The female sharks whelp just off the coast where I used visit in North Carolonia, and in June, the fishermen would catch scores of young blacktips and bonnetheads from the shore.

But I’ve never seen anything like that here.

But as I was walking along, I noticed a brown triangle poking above the foamy wayes. As I walked closer, a distinctive shark tail appeared behind the triangle. I knew instantly what I was observing. It was a sandbar shark. it was only about 3 or 4 feet long, and it was probably chasing small bait fish that it had chased into the surf.

What amazed me was the shark was only about ten feet from the beach in about 18 inches of frothing water.

Now, I’ve always been fascinated by sharks. My grandparents took me to the beach when I was about two, and according to my grandpa, he took me on a beach combing expedition, when we came across a ghastly sight. A large hammerhead, which could have been a bonnethead, had been caught by a fisherman. It had been fileted, and the rest of its body was left to lie there on the beach.  According to him, I was so fascinated by the creature that he knew that the next thing to do was to take me to the local aquarium. And so fascinated was I by all the fish at the aquarium that he had to take me three times a day on that particular vacation.

To see that sandbar shark rise from the surf took me back to that time. I long for that childlike sense of wonder, back when I was a fully subjective human being without all of this rationality to cloud my thinking.

I saw the sandbar shark for only a few brief seconds. Then the waves crashed down upon it, and it swam back into the depths. But for a brief moment, I was a child again.

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