Is the World's Largest Shark Shrinking?

Humans have over-exploited the whale shark -- the world's largest living fish -- to such a degree that the ocean giants are actually shrinking in size, according to new research.

The whale shark population has also fallen by approximately 40 percent over the past decade in Western Australian waters, the new study has found, suggesting that this once prevalent shark, which can reach lengths up to 42 feet, is undergoing a severe decline in certain regions.

"We are all very alarmed at our findings, which really did defy our expectations," co-author Ben Fitzpatrick, a University of Western Australia biologist, told Discovery News.

The researchers analyzed the largest-ever database of sightings and size information on whale sharks. The database represents a long-term, continuous record of sightings -- 4,436 in total -- as well as photo ID information concerning age and size, all pertaining to whale sharks at Ningaloo Reef, Western Australia.

Because the sharks gather seasonally at the picturesque reef from March to June, a profitable industry has been built around "dive with sharks" activities. Usually by air sightings, tour operators regularly gather information on the sharks, compiled in the extensive database.

Fitzpatrick and his colleagues not only detected the population drop at the reef, but they also discovered the sharks have shrunk in body length by an average of over 6.5 feet. The overall reduction appears to be due to the disappearance of older, larger females, along with some males, within whale shark groups.

"I think it is mostly because the larger animals are being hunted for food and other products, such as for soup fins," explained Barry Brook, another co-author of the study and director of the Research Institute for Climate Change and Sustainability at The University of Adelaide.

"The larger the fin, the more valuable it is," Brook added.

The findings are published in the latest issue of Biological Conservation.

The scientists believe a selection effect may also be at work, whereby pressures are forcing smaller, younger whale sharks to breed earlier, but they believe this is just "a minor piece of the puzzle."

Brook said that while the whale sharks enjoy protection in Ningaloo Reef waters, the sharks migrate over large distances, often traveling thousands of miles.

"Artisanal fisheries via harpoons for meat, for example, off the coasts of India and Indonesia, but mostly by Taiwanese and Chinese commercial fisheries" are likely responsible for the declines, he said, adding that whale shark meat is referred to as "tofu fish" due to its texture, which is also prized in shark fin soup and Chinese medicine.

Ship strikes also tend to kill larger adults, he said, though evidence for the strikes is hard to compile since resulting deaths would usually remain unknown.

These latest findings counter a study late last year by Brad Norman and Jason Holmberg of ECOCEAN, a research education and conservation organization. That report, based on multiple underwater images of the sharks, concluded that Ningaloo Reef whale sharks are thriving. Norman did, however, admit to Discovery News that the species is "rare" and "vulnerable to extinction."

Brook and his colleagues have authored a written response to Norman's paper, which is still under consideration by the journal, Ecological Applications. They say that while whale sharks receive some trade protection from the Convention on International Trade in Endangered Species, "it is difficult to police non-international trade or local hunting by indigenous people."

The migratory habits of whale sharks, Brook said, "mean it is impossible to protect the Ningaloo population once the sharks leave Australian waters for Indonesia and the Philippines."

The researchers urge officials to establish well-enforced international protection for the sharks. They also hope that collaborative tagging studies in the future will help to better identify and monitor whale shark migration routes.

Distant Wildfires Cause Arctic Cooling

It's hard to imagine that the raging blazes of wildfires could cool things down, but that is the conclusion of a new study.

Robert Stone of the University of Colorado, Boulder, and colleagues report that wildfire smoke that reaches the Arctic has the net effect of cooling the surface by reducing the amount of sunlight that makes it through.

The effect of smoke and other aerosol particles in the atmosphere is a large source of uncertainty in climate models. The new work removes some of that uncertainty.

"They have given us a much better understanding of what the effect of smoke is on the climate system," said Alan Robock of Rutgers University in New Brunswick, N.J.

The team made measurements in 2004 when widespread wildfires in Alaska and western Canada sent large plumes of smoke into the Arctic, including over their research station in Barrow, Alaska.

They measured the density of the smoke in the atmosphere and the net amount of energy from the sun hitting the surface to find the relationship between the amount of smoke and the reduction in energy reaching the ground.

When plugged into models, this information helped predict how the smoke would behave over other surfaces, such as the ocean, where the researchers could not make measurements.

The team found that smoke particles tend to absorb energy well above ground, but because they also reflect incoming radiation, the net effect at the surface is cooling. They published their results today in the Journal of Geophysical Research-Atmospheres.

The effect is greatest over dark surfaces, including the ocean, where most of the energy that makes it through is absorbed. Smoke still reduces the amount of radiation that hits ice-covered surfaces, but since these bright areas already reflect most of the radiation that hits them, smoke cover doesn't change the net amount of energy at the surface by as much.

"If the climate warms and you have more severe and frequent wildfires, that will have this tendency to cool the surface," Stone said. It is not yet possible to say how significant of an effect this might be, he added.

California's ongoing wildfires are unlikely to have a large effect on the Arctic, he said, because circulation patterns don't favor California's air masses reaching the Arctic.

However, "every year there are tremendous natural wildfires in Siberia," Stone said. "Once they take off they can burn for weeks and months." That air is readily carried to the Arctic, he added.

The smoke may have additional effects that Stone's models don't account for. For instance, the warming effect of smoke particles at higher altitudes may evaporate clouds, or the particles may also act to seed cloud formation, increasing cloudiness.

"This is a natural phenomenon, in that lightning starts the fires," Robock said. "But it's an anthropogenic phenomenon if the trees are more susceptible to fires because of greenhouse gases."

Earth, As E.T. Would See It

In the ongoing quest to find life elsewhere in the universe, it helps to have a role model. Presently, however, there's just one to choose from: Earth.

"It is terra-centric of us," said planetary scientist Sara Seager. "It's like that story of a person who loses their keys on a dark sidewalk and looks for them under the street light because that is the only place he can see."

Seager, with the Massachusetts Institute of Technology, is among dozens of researchers in the hunt for Earth-like worlds. She spends her time modeling what the atmospheres and interiors of planets outside our solar system might look like. Many of her ideas come from the home planet.

"If we get data, we want to know what it means," she said in an interview with Discovery News.

Twinkle, Twinkle

For example, at a planet-hunters conference in France last month, researchers reported that from the perspective of space, light from Earth twinkles as clouds pass in and out of view.

"A distant extraterrestrial observer would see Earth as a point source of light that varies in brightness in a repeating, predictable pattern, just like spots on a spinning ball," Science magazine reported in an article last month about the research, which was headed by Enric Palle of the Institute of Astrophysics of the Canary Islands.

If similar patterns were discovered on an extrasolar Earth, scientists might be able to look for what would appear to be variations in the planet's rotation, a phenomenon actually due to clouds.

On Earth, clouds indicate the presence of water vapor, and water, as far as scientists know, is a key ingredient for life.

This sort of detective work is what scientists searching for habitable planets have available. Direct imaging of large planets, let alone smaller Earth-sized worlds, is not possible with the telescopes and technologies that exist today.

The Next Pale Blue Dot

Even with the sophisticated observatories in the planning stages, such as NASA's Terrestrial Planet Finder, scientists' best hope is to discern a pale blue dot.

Their most important tool will not be a camera, but a spectrograph, which can split light bouncing off a target planet into individual wavelengths, much like visible light can be broken into a rainbow array of colors. Chemicals in a planet's atmosphere will absorb particular wavelengths, resulting in dropouts, like black lines in the rainbow.

"So from afar, we can see that there's water vapor, for example, which may be an indication of water on the planet's surface," Seager explained. "We can detect oceans, maybe weather."

After water, oxygen would be the next key find. Earth's atmosphere is rich with oxygen due to plant life. Uninhabited sister planet Venus, in comparison, has just a trickle.

"You can't generate that much oxygen by geologic processes," Seager said. "Life produces the same thing that can be produced naturally but, there's lots more of it."

Earth From a Distance

Among Seager's projects is a recycled asteroid probe now on an extended mission to hunt for extrasolar planets as it makes it way toward a comet. NASA on Thursday released one of the first offerings from Deep Impact's second life: a movie of Earth.

"It helps the search for other life-bearing planets in the universe by giving insights into how a distant, Earth-like alien world would appear to us," said University of Maryland astronomer Michael A'Hearn, the lead scientist for the Deep Impact extended mission, called EPOXI.

For example, in the video, sunlight can be seen bouncing off Earth's oceans.

"Similar glints to be observed from extrasolar planets could indicate alien oceans," said Drake Deming, with NASA's Goddard Space Flight Center in Greenbelt, Md.

The team also found eye-popping reflections of the planet's plant-covered continents in near-infrared imagery taken by Deep Impact.

"They're brighter in that wavelength," Seager observed. "I didn't really appreciate how that makes the continents stand out until I saw it."

Tiny Bug Threatens to Take Down U.S. Citrus Crops

Border agents have stepped up searches and hundreds of traps have been placed on the California-Mexico line in an aggressive campaign to stop a tiny bug from bringing in a disease farmers say could wipe out the $1.3 billion citrus industry here.

Already, Asian citrus psyllid has hurt citrus production in parts of China and infested millions of dead and dying trees in Florida and Brazil. Growers say the bug has the potential to be more damaging than the Mediterranean fruit fly because entire groves -- not just fruit -- are at risk.

"This is not one more thing, this might be the last thing," said Al Stehly, who manages 200 acres of oranges near Valley Center in San Diego County.

The tiny psyllids are the only transmitters of the disease, officially known by its Chinese name, huanglongbing, or "yellow dragon disease" for its visual effect on leaves. In the U.S., growers call it "citrus greening" disease because fruit fails to ripen.

Psyllids feed on the liquid inside citrus leaves, and once a psyllid eats from an infected tree, it carries the bacteria for life. Diseased trees wither and die within a few years.

More than 22 years of research by the U.S. Department of Agriculture has not yet revealed genetic or biological controls for the disease.

"There is no place in the world this disease is under adequate control," said plant pathologist Tim Gottwald of the USDA's agricultural research service in Florida and one of the world's leading authorities on citrus greening. "We don't have an adequate strategy at this moment."

Gottwald likens the potential impact to Dutch elm disease, which has wiped out nearly the entire elm population in England and Europe.

Recent news that the bug was found within four blocks of the San Diego County line sent orange juice futures up and spread panic through the industry. Industry officials worry international trade could be affected, as California supplies 85 percent of the U.S. fresh orange market, and 30 percent of the state's production is shipped overseas.

"The sky could fall unless everybody is constantly on top of everything on this," said Christopher Mundt, a plant epidemiologist at Oregon State University who studies grains, but was asked recently to bring fresh eyes to the citrus problem. "There's not going to be much room for error on this one."

DNA tests on 138 psyllids trapped so far in Tijuana have given no indication those bugs carry the bacteria.

Still, officials are being vigilant.

Border patrol agents have stepped up monitoring for orange tree cuttings and even certain types of curry leaves at airports and crossings. Some nursery ornamentals such as mock oranges and certain orange jasmines can be silent carriers of the disease. Officials also worry that citrus greening already could be present in California but until now has lacked a carrier.

California agricultural officials have placed 1,065 traps in a 120-square-mile grid at the border in San Diego and Imperial counties.

"Unfortunately, pests don't observe international borders," said Steve Lyle of the California Department of Agriculture. "Should the pest cross the border, and there's little reason to believe that it won't, we'll be able to detect it as fast as we can."

After that, agriculture officials say they aren't sure what they'll do and that "response options are under evaluation."

The California Citrus Research Board also is launching its own fight Friday, enlisting growers and master gardeners from San Diego to Ventura to help bait and trap the bug by pruning sentinel trees to encourage the new growth the psyllids favor. It will form a line of defense against the San Joaquin Valley, where 80 percent of the state's oranges grow.

The group, funded by state growers, will also set up labs in Riverside and Tulare counties to expedite testing for the disease on suspect trees. The cost will be about $1.5 million a year.

"We're throwing everything at it but the kitchen sink," said Ted Batkin, the board's president.

The bugs arrived in the U.S. in Florida in 1998, and the disease was in full-swing by 2005. Costly spraying of a variety of insecticides toxic to bees

Florida growers have contributed more than $20 million for research this year.

When the disease hits, growers must decide whether to cull and replace trees, or abandon operations.

"We can slow it down," Stehly said, "but we can't stop it. I'll be out of business in a few years."