Science Digest

Monday, May 11, 2009

Case Closed On Shark Mystery

How do you lose the world's second-largest fish?

It had been happening for decades to researchers studying the basking shark, a plankton-eating species that can grow to be 35 feet long -- only the whale shark is bigger. Basking sharks were easy to spot in summer and fall. Many cruised near the surface off New England, filtering water through an impossibly wide mouth.

But then, in winter, the sharks vanished from these waters, and scientists couldn't find them anywhere else. One guess was that they sank to the bottom and hibernated, waiting out a food shortage. But nobody knew for sure: The basking shark became a reminder of the unsolved mysteries of the oceans.

Last week, however, a group of researchers from Massachusetts and Maine said they had found the answer. Like many New Englanders, the basking sharks spend their winters in the Caribbean.

The scientists, whose study was published in the journal Current Biology, had tagged 25 sharks off Cape Cod with tracking devices, designed to release from the animals' skin after days or weeks and transmit data about where it had been.

Soon, the tags began popping up in places that nobody expected a basking shark to be: near the Bahamas, off Puerto Rico, even the mouth of the Amazon River in Brazil. The sharks had remained undetected because they stayed so deep, between 650 and 3,300 feet, that they were not caught in fishing gear.

There is more plankton in warmer waters, scientists said -- but it would be abundant enough off Florida, so there would be no reason to visit Brazil. Gregory B. Skomal of the Massachusetts Division of Marine Fisheries said there could be another reason drawing the sharks south. Female sharks could be giving birth and raising young in tropical waters.

"We've never seen pregnant females, and we've never seen a newborn basking shark," he said -- and that could be because they haven't been looking in the right place. Skomal said the data could be used to add protections for the sharks in the newly discovered habitat.

-- David A. Fahrenthold

Skin Color Linked To Smoking Risk

African Americans may be at greater risk for cigarette addiction and smoking-related disease than whites, and darker-skinned African Americans may be at higher risk than those who are lighter-skinned, because the pigment responsible for dark skin color appears to play a role in nicotine addiction and disease, researchers said last week.

Melanin, the coloring pigment in skin and hair, has a biochemical affinity for nicotine, the drug that smokers crave. The greater the amount of melanin people have, the harder it could be for them to quit smoking, according to a report in the journal Pharmacology, Biochemistry and Behavior.

The researchers found an increased risk of addiction not only among people who had darker skin as a result of their genes but also among people whose skin had been darkened as a result of exposure to sunlight. In both cases, those with the darkest skin tended to smoke the largest number of cigarettes.

One implication of the research is that studying smokers at different times of the year could produce different results, because of varying amounts of sunlight.

"One of the questions we want to address is why African Americans have lower quit rates than whites," one of the authors, Gary King, a professor of biobehavioral health at Penn State, said in a statement.

-- Shankar Vedantam

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