A new U.S. Geological Survey study shows how mercury pollution contaminates fish in the North Pacific
A federal study released today explains for the first time the link between global mercury emissions and the contamination of tuna and other marine life in the North Pacific Ocean.
The U.S. Geological Survey study [pdf] documents the formation in the North Pacific of methylmercury, a highly toxic form of mercury that rapidly accumulates in the food chain to levels that can cause serious health concerns for people who consume seafood. Scientists have known for some time that mercury deposited from the atmosphere can be transformed into methylmercury, but the study focuses on how that transformation occurs.
USGS showed that methylmercury is produced in mid-depth ocean waters by processes linked to “ocean rain.” Algae, which are produced in sunlit waters near the surface, die quickly and “rain” downward to greater water depths. The settling algae are decomposed by bacteria and the interaction of this decomposition process in the presence of mercury results in the formation of methylmercury.
Many steps up the food chain later, predators like tuna receive methylmercury from the fish they consume, the study shows.
The study unexpectedly reveals the significance of long-range movement of mercury within the ocean that originates in the western Pacific Ocean, off the coast of Asia, USGS scientist and co-author David Krabbenhoft said.
“Mercury researchers typically look skyward to find a mercury source from the atmosphere due to emissions from land-based combustion facilities,” Krabbenhoft said in a statement.
“In this study, however, the pathway of the mercury was a little different. Instead, it appears the recent mercury enrichment of the sampled Pacific Ocean waters is caused by emissions originating from fallout near the Asian coasts. The mercury-enriched waters then enter a long-range eastward transport by large ocean circulation currents.”
The Obama administration said the study demonstrates the need to curb global mercury emissions.
“This unprecedented USGS study is critically important to the health and safety of the American people and our wildlife because it helps us understand the relationship between atmospheric emissions of mercury and concentrations of mercury in marine fish,” Interior Secretary Ken Salazar said in a statement.
Scientists have predicted an additional 50 percent increase in mercury in the Pacific Ocean by 2050 if mercury emission rates continue as projected. USGS water sampling shows mercury levels in 2006 were approximately 30 percent higher than those measured in the mid-1990s.
“This study gives us a better understanding of how dangerous levels of mercury move into our air, our water, and the food we eat, and shines new light on a major health threat to Americans and people all across the world,” EPA Administrator Lisa Jackson added. “With this information in hand, plus our own mercury efforts, we have an even greater opportunity to continue working with our international partners to significantly cut mercury pollution in the years ahead and protect the health of millions of people.”
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The aesthetic appeal of symmetry is obvious whether you are a child playing with a kaleidoscope or a Great Mogul emperor building the Taj Mahal as a monument to eternal love. That preference, as it turns out, greatly shapes how we see the world when items are in motion. More on that shortly.
In the natural, as opposed to man-made, world, symmetry—whether we see it in prey, predator, mate or mother—serves as an early-alert system, drawing your attention. Even an infant, who has blurry views of his or her surroundings because of not yet developed acuity, has an innate preference for symmetry. Babies stare longer at faces that have two eyes in the normal position than they do at those that have a cyclopean or a stacked-eyes configuration.
Symmetrical faces tend to be judged as more attractive than asymmetrical ones. Some researchers have postulated that this partiality may be because infestation with parasites can cause visible asymmetry in victims. As a parasite species evolves, it continuously tries to match its surface antigens to those of its host to evade immunological rejection. At the same time, there is a strong selection pressure on the host to be able to detect parasitic infestation and other abnormalities that might potentially reduce fitness and reproductive success. If parasitic infestation occurs sufficiently early in development, it can produce minor deviations from symmetry—hence the adaptive advantage of using asymmetry as a marker to avoid potential mates with poor health, weak genes or a challenged immune system.
Balance on the Whole
Early in the 20th century Gestalt psychologists started exploring the perceptual importance of symmetry. They rejected and attacked the prevailing atomistic, or reductionist, approaches to perception. The Gestaltists, beginning with Max Wertheimer, identified “laws” of perceptual organization and emphasized how the relation of all the elements in a scene, rather than the individual elements by themselves, will influence the final perception. For example, three collinear dots suggest a line, but three dots when misaligned will evoke an unmistakable perception of triangleness—even though the display lacks the shape’s hallmark of three lines and three vertices (a).
The illustration in b demonstrates one of the most basic Gestalt principles—organization of a scene into “figure” and “ground.” Even in novel, abstract images, a perceptual division exists between an object, or thing, and the background. Contours are seen to belong to the figure, which is seen to be lying in front of the shapeless ground. Here you see a black vase , but with some time and effort, you should be able to perceive an alternative percept of two white faces in profile in front of a dark ground.
Gestaltists identified many “laws” for determining what is seen as figure or ground in a display. In general, if contours are near each other, they will be perceived as belonging together, as being part of the same figure, a tendency termed the Law of Proximity. If contours are mirror-symmetric, they also will group together and define a figure, known as the Law of Symmetry.
So what happens when symmetry is pitted against proximity? Symmetry tends to dominate; that is, we usually see the shapes defined by mirror-symmetric contours as figure rather than as ground (c). Our brain is choosing symmetry to perceive objects.
Now we return to the idea of considering how symmetry can influence the processing of motion. Let us begin with apparent motion, the illusion of movement that you get when, for instance, two spatially separated spots are presented in rapid temporal succession (as in a string of Christmas bulbs that appear to jump back and forth). Even though the spots/bulbs themselves do not budge, your perception of motion between them is vivid. Because the same brain mechanisms appear to process real motion (your cat walking across the room) and apparent motion (holiday lights), apparent-motion displays provide a convenient tool for the study of motion perception.
RENO, Nev. – Conservationists say livestock grazing poses a threat to a wide variety of fish and other wildlife across more than three-fourths of their dwindling habitats onin the West.
Using satellite mapping and federal records, WildEarth Guardians began a study last year matching wildlife habitat and U.S. grazing allotments across more than 260 million acres of federal land in the West.
It includes practically all of the remaining habitat of the Greater sage grouse, a hen-sized game bird the U.S. Fish and Wildlife Service is considering adding to the list of threatened or endangered species in 11 Western states from California to Wyoming. The environmental group wants the bird protected.
“The results confirm — in graphic form — previous research finding that incessant, ubiquitous public lands grazing has contributed to the decline of native wildlife,” concludes the report entitled “Western Wildlife Under Hoof.” The report is scheduled to be released Friday.
The group said continued grazing in ever-shrinking habitat hampers the recovery of fish and wildlife and in some cases threatens them with extinction.
Cattle and sheep trample vegetation, damage soil, spread invasive weeds, spoil water and deprive native wildlife of forage, the report said. It notes that then-Interior Secretary Bruce Babbitt said in 2005 that livestock grazing “is the most damaging use of.” (emphasis added)
Mark Salvo, WildEarth Guardians’ grazing program specialist and author of the report, said the new data suggest livestock have “done more damage to the Earth than the chain saw and bulldozer combined.”
Jeff Eisenberg, director of federal lands for the National Cattleman’s Beef Association, criticized the findings as part of an effort to shut down grazing on federal lands.
“There’s a number of environmental groups that have decided the best way to spend their time and the money of their funders is to eliminate the families and communities that have made the West what it is today,” he told AP in an e-mail. “These groups don’t deserve a dignified response.”
Don Kirby, president of the Society for Range Management and director of North Dakota State University’s School of Natural Resource Sciences, said livestock grazing is an important part of a “landscape management toolbox” that can be used to reduce wildfires and improve wildlife habitat.
“Western rangelands and the wildlife species that live there have coexisted with grazing by large herbivores for tens of thousands of years,” Kirby said.
The report found livestock grazing is permitted on 91 percent of the Greater sage grouse’s habitat and that grazing operations are active on 72 percent of the habitat. Grazing is active on 55 percent of the federal range of the Gunnison sage grouse and is permitted on 84 percent of it.
Likewise, grazing is permitted on about 80 percent of public land in the historic range of several cutthroat trout species, including 88 percent of the Lahontan and 76 percent of the Bonneville.
It’s also permitted on about 75 percent of the federal habitat of four species of prairie dogs.
“The species included in our report are representative of the hundreds of wildlife species that are threatened by public lands grazing,” said Salvo, whose group has offices in Colorado, New Mexico and Arizona.
The bulk of the federal land studied is managed by the , which issued grazing permits and leases to 15,799 ranchers and other operators covering 128 million acres of U.S. land in 2006.
BLM spokesman Jeff Krauss said the agency has not fully reviewed the report but maintains “well-managed grazing provides numerous ecological and environmental benefits.”
Among other things, WildEarth Guardians recommends buying out permits from ranchers and others willing to remove their livestock from grazing land.
“There is a greater economic value in non-consumptive uses of public land — hunting, fishing, birdwatching, hiking, camping — than livestock grazing,” the report said.
Theshares concerns about dwindling wildlife populations but believes there is a place for grazing on public land, spokesman Chris Healy said.
If ranchers end up selling their land, it could be subdivided and lead to development even more problematic for wildlife, he said.
“It behooves us to get everybody who uses the land to be part of the solution and that’s what we’ve been trying to do with the sage grouse. If one sector or user of the land feels like they are being ganged up on, the odds of coming up with a solution that will work are not good,” he said.
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