joi, 18 septembrie 2008

'Day-Glo' Fish Shine Red Light

Seeing Red
- It was staring them in the face, but somehow generations of marine biologists have failed to notice that a lot of fish in the sea glow a fluorescent red, according to a study published Monday.

This unheralded talent for neon-like crimson displays is more than a curiosity, and is sure to create waves -- and a bit of embarrassment -- among ichthyologists, as fish experts are called.

It has long been axiomatic that red light is simply not part of the mental universe of marine fish because the sunlight's longest visible wavelengths do not penetrate below a depth of 30 feet.

A fire-engine red diving suit at 65 feet, for example, will appear dark grey or black to anyone -- or any fish -- that happen to be in the vicinity.

Dive far enough beneath the surface, and there is simply no red to be seen.

This foreshortening of the color spectrum under the waves was also assumed to correspond to a narrowed field of vision in fish, said the study's lead researcher in an interview.

"The general consensus, which dominated fish literature for 20 or 30 years, was that fish don't see red very well or at all," explained Nico Michiels, a researcher at the University of Tubingen in Germany.

From an evolutionary standpoint, in other words, why develop a skill that you will never be able to use?

But conventional wisdom, it seems, was flat-out wrong.

"We have been blinded, literally, by the blue-green light that is available on reefs in the daytime," said Michiels.

At least 32 species of reef fish -- including pygmy gobies and some wrasses -- can shine like a red Christmas bulb, not by reflecting sunlight but by emitting their own, the study found.

Dissection revealed that the fluorescence originates in guanine crystals, a chemical compound that is added to nail polish and car paint to give added luster.

And because the light is coming from the fish themselves, it remains visible at depth and is easily seen -- but only at close distances.

Michiels and his colleagues saw the light, as it were, by accident.

Looking through a filter while scuba diving that blocked out the brighter green and blue light waves, leaving only red ones, they suddenly saw a whole universe of sea creatures glowing various hues of cherry, crimson, ruby and rust.

"Besides fish, there are lots of fluorescent organisms on the reef, including algae, coral and other small organisms," Michiels said.

That some fish glow is certain, and was confirmed using spectrometry in laboratory experiments. It is also very likely that many can see red perfectly well, and do so for a reason.

One possibility is that they emit the color -- visible only within a small circumference -- as a means of intimate communication, perhaps for mating or to signal danger.

There is also evidence that turning red could serve as a kind of camouflage.

"It may seem strange, using fluorescence to make yourself invisible," Michiels said. "But fish that sit on a reef have a lot of fluorescence around them, so they blend in."

The next step is to figure out how day-glo fish might use their color-generating power to exchange information. Adapting techniques proven in other experiments with fish, Michiels is creating an environment in which fish can court each other via video.

By controlling which part of the color spectrum the fish can see, the researchers will seek to verify that some fish do, indeed, see red.

luni, 15 septembrie 2008

Antarctic Krill Found at Crushing Depths

Hearty Prey
Hearty Prey
- Scientists have discovered Antarctic krill living and feeding at crushing depths of 3,000 meters (9,800 feet) in waters around the Antarctic Peninsula, according to a study released Monday.

Until now the shrimp-like crustaceans were thought to only live within several hundred meters (yards) of the ocean surface, the study said.

The discovery radically changes the scientific understanding of the major food source for marine animals including fish, squid, penguins, seals and whales, said the study, published in the journal Current Biology.

"Most krill make their living in the ocean's surface waters," said Andrew Clark of the British Antarctic Survey.

"It was a surprise to observe actively feeding adult krill--including females that were apparently ready to spawn--close to the seabed in deep waters."

Antarctic krill feed on tiny phytoplankton and live in schools, called swarms, sometimes reaching densities of 10,000 individuals.

A key link in the Antarctic food chain, they grow to lengths of six centimeters (2.4 inches) and weigh up to two grams (0.7 ounces). They have a lifespan of up to eight to ten years.

Researchers from the British Antarctic Survey and the National Oceanography Center in Southampton used a deep-diving, remotely operated vehicle to film the krill in the nearly pitch-black depths.

Antarctic Warming Creating Predator 'Smorgasbord'

Headed South?

- Global warming is setting the stage for an invasion of predators on the sea floor around Antarctica, the likes of which have not been there for more than 40 million years.

Back in the late Eocene epoch, predatory animals such as sharks and crabs were driven away from Antarctic depths when the continent and its surrounding waters turned into an icebox, said researchers on Friday at a symposium at the meeting of the American Association for the Advancement of Science in Boston.

The result was a virtually predator-free zone on the seafloor and a paradise for worms, sea lilies, clams, brittle stars and other bottom-dwelling animals.

All that is about to end, however. Global warming is now raising water temperatures to the point where, very soon, those long-exiled predators could return and wreak havoc on the ocean floor, say biologists.

"It's going to be a smorgasbord," said researcher Cheryl Wilga of the University of Rhode Island. She studies the metabolic limitations of sharks that have kept them from Antarctic waters for millions of years, but may not do so much longer.

"The species in the Antarctic (seafloor) have no defense for shell-crushing predators," said extreme species researcher Brad Seibel, also of the University of Rhode Island. "I don't think that anyone was really aware of this issue."

Along the Antarctic Peninsula, the northernmost, warmest part of the continent, global warming is raising air temperatures quickly. Water temperatures have been warming as well, at a rate of about 0.04 degrees Celsius per year, Wilga says. That comes to about one degree per 25 years.

Compared to the relative stability seen for tens of millions of years, that's incredibly fast. Already, crabs are showing up, and some sharks are poised to pounce once the thermal dinner bell rings.

Antarctic King Crab?

The first exiled predator to return to Antarctica is the king crab. The leggy crustaceans have been found way down on the deep slopes off the Antarctic continental shelf -- where the water is slightly warmer than elsewhere.

There they are fighting the cold, explained marine scientist Richard Aronson of Dauphin Island Sea Lab and the University of South Alabama.

The frigid water makes it hard for the crabs to efficiently flush magnesium out of their bodies, said Aronson. Too much magnesium acts like a narcotic on a crab.

"When it's too cold, the magnesium makes them pass out and die," Aronson said. That's probably why the crabs have been absent for eons. Now, however, in those slightly warmer depths off the continental shelf, it's just warm enough for the crabs to survive there.

As the upper waters continue to warm, nothing will stop the king crabs from moving up onto the continental shelf and feasting. That will "hammer" the old seafloor communities, Aronson said.

"We expect the populations (of seafloor invertebrates) to take a dive," said Aronson.

Giant Starfish, Lilly Fields Found in Antarctic Waters

Well-Fed Starfish

- Scientists who conducted the most comprehensive survey to date of New Zealand's Antarctic waters were surprised by the size of some specimens found, including jellyfish with 12-foot tentacles and 2-foot-wide starfish.

A 2,000-mile journey through the Ross Sea that ended Thursday has also potentially turned up several new species, including as many as eight new mollusks.

It's "exciting when you come across a new species," said Chris Jones, a fisheries scientist at the U.S. National Oceanic and Atmospheric Administration. "All the fish people go nuts about that -- but you have to take it with a grain of salt."

The finds must still be reviewed by experts to determine if they are in fact new, said Stu Hanchet, a fisheries scientist at New Zealand's National Institute of Water and Atmospheric Research.

But beyond the discovery of new species, scientists said the survey, the most comprehensive to date in the Ross Sea, turned up other surprises.

Hanchet singled out the discovery of "fields" of sea lilies that stretched for hundreds of yards across the ocean floor.

"Some of these big meadows of sea lilies I don't think anybody has seen before," Hanchet said.

Dolphin Rescues Stranded Whales

Stranded? Try Me
Stranded? Try Me

- A dolphin guided two stranded whales to safety after human attempts to keep the animals off a New Zealand beach failed, a conservation official said Wednesday.

"I've never heard of anything like this before, it was amazing," Conservation Department officer Malcolm Smith said.

The actions of the dolphin, well known locally for playing with swimmers at Mahia beach on the east coast of the North Island, probably meant the difference between life and death for the whales, Smith said.

Smith had been working for over an hour and a half to save the two pygmy sperm whales which had repeatedly become stranded despite his attempts to push them back out to sea.

A bottlenose dolphin, named Moko by locals, appeared and guided the whales to safety after apparently communicating with them, Smith said.

The whales, a 10-foot female and her male calf, were apparently confused by a sandbar just off the beach and could not find their way back to open water.

Smith had been alerted at daybreak on Monday by a neighbor about the two stranded whales on Mahia beach near his home.

"Over the next hour and a half I pushed them back out to sea two or three times and they were very reluctant to move offshore," Smith said.

"I was starting to get cold and wet and they were becoming tired. I was reaching the stage where I was thinking it's about time to give up here, I've done as much as I can."

In that situation, whales are often humanely killed to end their suffering.

Smith said Moko arrived on the scene and he could hear the whales and the dolphin making noises, apparently to one another.

"The whales made contact with the dolphin and she basically escorted them about 200 yards parallel with the beach to the edge of the sandbar.

"Then she did a right-angle turn through quite a narrow channel and escorted them out to sea.

"There's been no sign of the whales since Monday, they haven't re-stranded."

"What the communication was I do not know, and I was not aware dolphins could communicate with pygmy sperm whales, but something happened that allowed Moko to guide those two whales to safety."

Moko has become famous for her antics at Mahia, which include playing in the surf with swimmers, approaching boats to be patted and pushing kayaks through the water with her snout.

Such close interaction with humans is rare among dolphins but not unknown. "She's become isolated from her pod obviously for one reason or another, but obviously made Mahia home just at the moment."

Mahia gets up to 30 whale strandings a year, most of which end with the whales having to be put down.

"I don't know if next time we have a whale stranding we can get her to come in again. She certainly saved the day for us and the whales this time."

North American Fish Under Threat

Keen SniffersaPacific Salmon
Pacific Salmon | Video: Discovery Earth

- Nearly 40 percent of fish species in North America are imperiled, according to a new survey by fish experts, the U. S. Geological Survey, and the American Fisheries Society, up 92 percent from the last survey done in 1989.

North America hosts perhaps the greatest diversity of temperate freshwater organisms on Earth, including aquatic insects, mussels, crayfish and fish.

The new report, compiling assessments from fish experts in the United States, Canada and Mexico, found that of the 700 types of fish in the survey, 230 are "vulnerable," 190 are "threatened," 280 are "endangered," and 61 are believed extinct.

"A lot of effort has been expended since 1989, but things are still in a sorry state in many ways," said study author Eric Taylor of the University of British Columbia in Vancouver. "We can't be complacent with trying to address some of these declines."

No single cause explains the ongoing fish losses, Taylor and others agree. Habitat loss, invasive species, diseases, dams, and water contaminants all contribute.

"Fish are kind of canaries in the coal mine," said Howard Jelks of the USGS and lead author of the report, published in Fisheries. "If you change the water to something that's not able to support these fish, it's also not going to be as high quality for recreating, for eating the fish out of these streams, for drawing water that's ultimately used for drinking, or for other things."

Certain regions were identified as hotspots with both high fish diversity and high degrees of threat. These included the Pacific central valley, the western Great Basin, the Rio Grande, and several river systems in the southeast such as the Tennessee and Mobile.

Pacific Coast salmon and trout were among the most at-risk types of fish, as were minnows, suckers, and catfish across the continent. Almost half of the carp and minnow family and the family of fish including perch and darters were identified in one of the imperiled categories.

The new report lists distinct sub-populations of certain fish separately, even if they are classified as the same species, which accounts for part of the increase.

joi, 11 septembrie 2008

Fish to Be Trained to Jump Into Nets

Jump, Roll Over

- Call them Pavlov's fish: Scientists are testing a plan to train fish to catch themselves by swimming into a net when they hear a tone that signals feeding time.

If it works, the system could eventually allow black sea bass to be released into the open ocean, where they would grow to market size, then swim into an underwater cage to be harvested when they hear the signal.

What's next, teaching them to coat themselves in batter and hop inside a fryer?

"It sounds crazy, but it's real," said Simon Miner, a research assistant at the Marine Biological Laboratory at Wood's Hole, which received a $270,000 grant for the project from the National Oceanic and Atmospheric Administration.

Miner said the specially trained fish could someday be used to bolster the depleted black sea bass stock. Farmed fish might become better acclimated to the wild if they can be called back for food every few days.

The bigger goal is to defray the costs of fish farming, an increasingly important source of the world's seafood. If fish can be trained to return to the farmer after feeding in the open ocean for several days, farms could save money on feed and reduce the amount of fish waste released in concentrated areas.

The key question for fish farmers: How many fish will actually return, and how many will be lost to predators or simply swim away?

Randy MacMillan, president of the National Aquaculture Association, said fish farmers won't be easily convinced to adopt open-ocean ranching.

"The commercial side is going to be skeptical," said MacMillan, who works on a trout farm in Idaho.

The Massachusetts project is one of several experiments funded by the federal government last year as part of aquaculture research.

"We're looking for innovations that will actually make a difference for coastal communities and the environment," said Michael Rubino, manager of NOAA Aquaculture. "It fits in both."

Previous experiments have used sound to train a fish to feed -- similar to what Russian scientist Ivan Pavlov did in his famous dogs that salivated at the sound of a bell, expecting food.

In Japan, scientists have used sound to keep newly released farmed fish in certain areas, where they could be caught in traditional ways.

But no one has ever tried to get fish to leave and return to an enclosure where they can be scooped up.

The project began last summer using 6,500 black sea bass, a stout, bottom-dwelling fish found between Florida and Cape Cod that migrates south of New Jersey in the winter. The species grows up to 3 pounds and 20 inches long and has a thick, white flesh that can be filleted for broiling or cut into nuggets for frying.

Miner said the first objective was to see if the fish could truly be trained. He got his answer after keeping the fish in a circular tank, then sounding a tone before he dropped food in an enclosed "feeding zone" within the tank that the fish could enter only through a small opening.

Researchers played the tone for 20 seconds, three times a day, for about two weeks. Afterward, whenever the tone sounded, "you have remote-control fish," Miner said.

"You hit that button, and they go into that area, and they wait patiently," he said.

Miner is now trying to figure out how long the fish remember to associate the tone with food. He feeds the fish outside the feeding zone without a tone for a few days and then tests if they will still head for the feeding area when the tone sounds again.