joi, 11 septembrie 2008

Colossal Squid Dissection Reveals Toothfish Diet

Big, Hungry Squid

Big, Hungry Squid

- Scientists examining the world's largest known colossal squid this week could find nothing in the cephalopod's stomach, suggesting the large marine animal was starving when it was captured in February of 2007.

That might help to explain why the squid was caught in the first place. The huge, jelly-like animal from Antarctica was voraciously eating an Antarctic toothfish hooked in a New Zealand long-line fishing operation in the Ross Sea when fishermen hauled up their catch, revealing the then half-dead, enormous squid.

View a slideshow of the colossal squid here.

The fishermen netted the squid and placed it in their vessel's freezer. It remained frozen until last week, when scientists at The Museum of New Zealand Te Papa thawed and analyzed the squid. Part of that investigation involved the insertion of an endoscope into the specimen's stomach.

"The endoscope revealed nothing," museum spokesperson Jane Keig told Discovery News. "Its stomach was empty."

Last week, the squid project's director, Carol Diebel, told Discovery News there were plans to remove tissue samples from the squid's stomach, but the researchers instead decided not to cut into the colossal squid, as "any kind of dissection could harm it" before the squid goes on public display in a specially constructed fluid-filled tank.

The Colossal Squid's Favorite Food

Diebel and her team instead focused their dissection efforts on yet another colossal squid housed in the museum. This second squid was laid out on a trough-like table next to the primary specimen for much of the week.

The stomach of that second squid yielded the remains of toothfish. Prior studies of colossal squid remains found in the stomachs of whales also revealed evidence of toothfish consumption, so scientists believe this fish could comprise a large portion of the colossal squid's diet.

The word "toothfish" generally refers to two closely related species: the Patagonian toothfish, popularly known as Chilean sea bass, and Antarctic cod, which is sometimes referred to as Antarctic toothfish. Both species possess a rather toothy, gaped mouth, hence the name, and can grow to around 7 feet or more in length.

Recently it was determined that the Antarctic toothfish possesses special proteins in its body that act like anti-freeze, preventing its blood from freezing into a solid block in the ice-laden, high latitude waters where it lives. Both the toothfish and the colossal squid favor deep water, 3,000 or more feet below the surface, and each has developed special adaptations to live and hunt in the darkness of that environment.

Hunting in the Dark

During this week's colossal squid investigation, the researchers were able to get an up-close look at the squid's tentacles. The tentacle tips -- appropriately called "clubs" -- are armed with two rows of sharp hooks that can swivel in all directions.

While no one has closely observed a colossal squid in hunting action, it's believed the animal moves quickly, grabbing toothfish and other prey with these spiked tentacles, which ironically somewhat resemble long-line fishing lines.

The scientists also discovered the squid has basketball-sized eyes, "the largest known in the animal kingdom," according to Diebel, along with a light organ right near the eye sockets. She believes this organ may function like a searchlight.

Toothfish also possess special eyes, with retinas that are well adapted to low light levels. While the mostly clear squid is nearly invisible in deep water, it's probable that colossal squid and toothfish play a continual hide and seek game of survival, where who spots whom first determines which one could live another day.

The Big Beak's Bite

The defrosted colossal squid's beak suggests the animal was much larger than it is now, a fact that's been supported by the men who witnessed the squid before it went into the freezer. Due to water and temperature changes, the squid shrunk to around 14 feet in length. Despite such alteration of the squid's flesh, its beak remains fully intact.

Among the colossal squid's many mysteries has been: How can an animal the consistency of firm Jell-O bite into prey without tearing itself to pieces?

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