'Silent extinctions' tied to human changes in habitat, experts say

WASHINGTON - About four out of 10 freshwater fish species in North America are in peril, according to a major study by U.S., Canadian and Mexican scientists.

And the number of subspecies of fish populations in trouble has nearly doubled since 1989, the new report says.

One biologist called it "silent extinctions" because few people notice the dramatic dwindling of certain populations deep in American lakes, rivers and streams. And while they are unaware, people are the chief cause of the problem by polluting and damming freshwater habitats, experts said.

In the first massive study of freshwater fish on the continent in 19 years, an international team of dozens of scientists looked not just at species, but at subspecies — physically distinct populations restricted to certain geographic areas. The decline is even more notable among these smaller groups.

The scientists found that 700 smaller but individual fish populations are vulnerable, threatened, or endangered. That's up from 364 subspecies nearly two decades ago.

And 457 entire species are in trouble or already extinct, the study found. Another 86 species are OK as a whole, but have subspecies in trouble.

The study, led by U.S. Geological Survey researchers, is published in the current issue of the journal Fisheries. Researchers looked at thousands of distinct populations of fish that either live in lakes, streams and rivers or those that live in saltwater but which migrate to freshwater at times, such as salmon that return to spawn.

Some vulnerable fish are staples of recreational fishing and the dinner plate. Striped bass that live in the Gulf of Mexico, Bay of Fundy and southern Gulf of St. Lawrence are new to the imperiled list. So are snail bullhead, flat bullhead and spotted bullhead catfish. Sockeye, Chinook, coho, chum and Atlantic salmon populations are also called threatened or endangered in the study. More than two dozen trout populations are considered in trouble.

About 6 percent of fish populations that were in peril in 1989, including the Bonneville cutthroat trout, have made a comeback, said lead author Howard Jelks of the U.S. Geological Survey. But one-third of the fish that were in trouble in 1989 are worse off now, said the Gainesville, Fla., biologist.

The study includes far more species and populations than those that are on the official U.S. government endangered species list.

Jelks said the number of species in trouble was close to double what he expected and that means people should be "considerably worried."

The biggest cause, Jelks said, is degraded freshwater habitat, both in quality and quantity of water for fish to live in. Invasive species crowding out native fish is also to blame, he said.

Fish "live in a freshwater habitat that's pretty much under assault by people," said Duke University marine biologist Larry Crowder, who wasn't part of the study. "Things are tanking all around us. When does it have to be bad enough to get people's attention?"

Many of the species in trouble or already extinct are small minnows and darters whose absence is little noticed, but they play a vital role in the food chain.

Hardest hit is Mexico where nearly half the fish species are in trouble. One in three species in the United States are in peril — up from about one in five in 1989. About 10 percent of Canadian species dwindled. In the United States, the most vulnerable populations are in the Southeast, not counting Florida.

In the U.S., 263 fish species are in trouble or are already extinct, and nearly 500 have no problems.

The number of fish species and subspecies in North America that went extinct rose from 40 to 61 since 1989.

Anthony Ricciardi, a McGill University biologist who was not part of the research, found that about 10 years ago freshwater extinctions were happening at a faster pace than on land or in the sea. And yet few people notice, he said.

"A lot of silent extinctions are happening," Ricciardi said. "What we're doing is widespread, it's pervasive and it's rapid."

ScienceDaily (Aug. 12, 2008) — Amphibians, reigning survivors of past mass extinctions, are sending a clear, unequivocal signal that something is wrong, as their extinction rates rise to unprecedented levels, according to a paper published by the Proceedings of the National Academy of Sciences (PNAS). Humans are exacerbating two key natural threats – climate change and a deadly disease that is jumping from one species to another.

The authors confront the question of whether Earth is experiencing its sixth mass extinction and suggest that amphibians, as a case study for terrestrial life, provide a clear answer. "A general message from amphibians is that we may have little time to stave off a potential mass extinction," write co-authors Vance T. Vredenburg, assistant professor of biology at San Francisco State University, and David B. Wake, curator of herpetology in the Museum of Vertebrate Zoology at University of California, Berkeley, in the August 12 issue of PNAS.

Amphibians are among the oldest organisms on earth, having survived the last four mass extinctions. The current extinction rate of amphibians is cause for alarm, according to biologists.

"An ancient organism, which has survived past extinctions, is telling us that something is wrong right now" Vredenburg said. "We -- humans -- may be doing fine right now, but they are doing poorly. The question, really, is whether we'll listen before it's too late."

While many factors have been cited for the profound change in global amphibian populations, a new emerging infectious disease, chytridiomycosis, is thought to be directly responsible for wiping out more than 200 species. It poses the greatest threat to biodiversity of any known disease. An aquatic fungus of unknown origin, it's the first of its kind to infect vertebrates, and only amphibians.

Understanding the ecology of chytridiomycosis may not only help amphibians, but human health. Scientists seek to map how the pathogen is transmitted from one species to another to develop ways to prevent or control outbreaks.

The Sierra Nevada Yellow-legged Frog is an example of a species under threat of extinction. In 2001, chytridiomycosis was detected in the mountains of the Sierra Nevada, and subsequently the authors have documented mass die-offs and the collapse of populations because of outbreaks. The fungus is surprisingly virulent, according to authors, and how it causes death is not yet known.

"It's important for people to understand what's infecting and killing these frogs," Vredenburg said. "This disease is a remarkable example of a pathogen jumping boundaries and causing havoc. If we can understand how it is able to do so, we may be able to help the frogs as well as ourselves."

David B. Wake served as the director of the Museum of Vertebrate Zoology (MVZ) for 27 years and is now curator of herpetology and professor of the Graduate School at the University of California, Berkeley. MVZ is a center for research and education in the biology of amphibians, reptiles, birds and mammals. Founded in 1908, the Museum's mission is to document and increase understanding of the diversity of terrestrial vertebrates, with particular emphasis on western North America.

Vance T. Vredenburg is an assistant professor at San Francisco State University. His research focuses broadly on the ecology, evolution and conservation of amphibians and incorporates elements of population, community and behavioral ecology to investigate the impacts of emerging infectious disease, introduced predators, and habitat loss on threatened amphibians. He is the co-founder of AmphibiaWeb.org (http://amphibiaweb.org) an online bioinformatics project promoting science and conservation of the world's amphibians.

ScienceDaily (Aug. 13, 2008) — Human activities are cumulatively driving the health of the world's oceans down a rapid spiral, and only prompt and wholesale changes will slow or perhaps ultimately reverse the catastrophic problems they are facing.

Such is the prognosis of Jeremy Jackson, a professor of oceanography at Scripps Institution of Oceanography at UC San Diego, in a bold new assessment of the oceans and their ecological health. Publishing his study in the online early edition of the Proceedings of the National Academy of Sciences (PNAS), Jackson believes that human impacts are laying the groundwork for mass extinctions in the oceans on par with vast ecological upheavals of the past.

He cites the synergistic effects of habitat destruction, overfishing, ocean warming, increased acidification and massive nutrient runoff as culprits in a grand transformation of once complex ocean ecosystems. Areas that had featured intricate marine food webs with large animals are being converted into simplistic ecosystems dominated by microbes, toxic algal blooms, jellyfish and disease.

Jackson, director of the Scripps Center for Marine Biodiversity and Conservation, has tagged the ongoing transformation as "the rise of slime." The new paper, "Ecological extinction and evolution in the brave new ocean," is a result of Jackson's presentation last December at a biodiversity and extinction colloquium convened by the National Academy of Sciences.

"The purpose of the talk and the paper is to make clear just how dire the situation is and how rapidly things are getting worse," said Jackson. "It's a lot like the issue of climate change that we had ignored for so long. If anything, the situation in the oceans could be worse because we are so close to the precipice in many ways."

In the assessment, Jackson reviews and synthesizes a range of research studies on marine ecosystem health, and in particular key studies conducted since a seminal 2001 study he led analyzing the impacts of historical overfishing. The new study includes overfishing, but expands to include threats from areas such as nutrient runoff that lead to so-called "dead zones" of low oxygen. He also incorporates increases in ocean warming and acidification resulting from greenhouse gas emissions.

Jackson describes the potently destructive effects when forces combine to degrade ocean health. For example, climate change can exacerbate stresses on the marine environment already brought by overfishing and pollution.

"All of the different kinds of data and methods of analysis point in the same direction of drastic and increasingly rapid degradation of marine ecosystems," Jackson writes in the paper.

Jackson furthers his analysis by constructing a chart of marine ecosystems and their "endangered" status. Coral reefs, Jackson's primary area of research, are "critically endangered" and among the most threatened ecosystems; also critically endangered are estuaries and coastal seas, threatened by overfishing and runoff; continental shelves are "endangered" due to, among other things, losses of fishes and sharks; and the open ocean ecosystem is listed as "threatened" mainly through losses at the hands of overfishing.

"Just as we say that leatherback turtles are critically endangered, I looked at entire ecosystems as if they were a species," said Jackson. "The reality is that if we want to have coral reefs in the future, we're going to have to behave that way and recognize the magnitude of the response that's necessary to achieve it."

To stop the degradation of the oceans, Jackson identifies overexploitation, pollution and climate change as the three main "drivers" that must be addressed.

"The challenges of bringing these threats under control are enormously complex and will require fundamental changes in fisheries, agricultural practices and the ways we obtain energy for everything we do," he writes.

"So it's not a happy picture and the only way to deal with it is in segments; the only way to keep one's sanity and try to achieve real success is to carve out sectors of the problem that can be addressed in effective terms and get on it as quickly as possible."

The research described in the paper was supported by the William E. and Mary B. Ritter Chair of Scripps Institution of Oceanography.

ScienceDaily (Aug. 5, 2008) — Most of the world's plant species rely on animals to transfer their pollen to other plants. The undisputed queen of these animal pollinators is the bee, made up of about 30,000 species worldwide, whose daily flights aid in the reproduction of more than half of the world's flowering plants.

In recent years, however, an unprecedented and unexplained decline in bee populations across the U.S. and Europe has placed the health of ecosystems and the sustainability of crops in peril.

In an oral session at the Annual Meeting of the Ecological Society of America, an interdisciplinary group of scientists will explore the problem of bee habitat loss at a broad scale to determine what can be done to preserve bees in their native habitats. The session, titled "The Landscape-Scale Ecology of Pollinators and Pollination," will include scientists in the fields of computer science, mathematics and ecology from institutions in the U.S., Europe and Asia.

The most recent and headline-capturing phenomenon, known as colony collapse disorder, is characterized by the disappearance of adult honeybees from beekeeper hives, leaving behind bee larvae with no caretakers. The bee decline is particularly unnerving for farmers because an estimated 80 percent of all food crops are pollinated by honeybees and their wild cousins.

Stymied scientists have proposed a host of reasons for managed honeybee declines, including climate change, parasites, diseases, overexposure to pesticides and loss of suitable habitat; most researchers believe that a combination of these factors is responsible. In this oral session, scientists turn their attention to native, wild bees to determine whether they are undergoing – or might undergo – the same decline.

One of the session's organizers, Neal Williams of Bryn Mawr College, hopes that the session will result in the synthesis of ideas from many disciplines. "We want to know: Can we look at landscape models in a predictive way and use those to inform us about natural populations and how they deliver pollinator services to crops?" he asks.

Rachael Winfree of Rutgers University is particularly interested in the health of native bees as "biological insurance" against the decline of honeybees. "Over half of the world's native plants require animal pollinators, and most of those are bees," she says. "Native pollinators are serving as a backup plan for the honeybee."

Winfree will present a study that combines data from over 50 published studies of bee population sizes and diversity. She found that in areas of extreme fragmentation due to human development, animal grazing, logging and crop fields, bee populations were smaller and the number of bee species was lower than in natural or minimally disturbed areas.

Scientists are also using technological methods to further understand bee communities. Daniel Chalk, a graduate student at the University of Exeter in the United Kingdom, used an artificial intelligence computer model to predict flight patterns of wild bumblebees. His model is useful because it can predict how bees would forage, or look for food resources, in different landscapes.

"Crucially, our model is able to predict the behavior of bees in larger-scale foraging environments, where the foraging patches can be thought of as large fields of crops," says Chalk. His model, he says, could help scientists understand how land disturbance caused by humans affects bee species richness and density.

Williams used an experimental approach to understand the landscape-scale ecology of native bumblebees. He and his colleagues established 38 bee colonies across central California, ranging from undisturbed chaparral to organic and conventional farms. During the course of the summer months, they found that the further a colony was from natural areas, the fewer worker bees it sustained. Williams' team also found that bees always collected pollen from both crops and native plants. Since crop fields aren't in bloom for the entire bee active season, Williams says, the bees need an adequate alternative source of nectar and pollen, and may travel several kilometers to find it. Therefore, a mosaic landscape that has natural areas mixed in with agriculture is important to keep bee colonies healthy.

"Today's landscape is both natural and managed," says Williams. "It's not just matrix of natural areas with agriculture mixed in, but a patchwork quilt with animals using all of the areas in the landscape."

ScienceDaily (Aug. 5, 2008) — Mankind's closest relatives – the world's monkeys, apes and other primates – are disappearing from the face of the Earth, with some literally being eaten into extinction.

The first comprehensive review in five years of the world's 634 kinds of primates found that almost 50 percent are in danger of going extinct, according to the criteria of the IUCN Red List of Threatened Species.

Issued at the 22nd International Primatological Society Congress in Edinburgh, Scotland, the report by the world's foremost primate authorities presented a chilling indictment on the state of primates everywhere. In Asia, more than 70 percent of primates are classified on the IUCN Red List as Vulnerable, Endangered or Critically Endangered – meaning they could disappear forever in the near future.

The main threats are habitat destruction, particularly from the burning and clearing of tropical forests that also emits at least 20 percent of the global greenhouse gases causing climate change, and the hunting of primates for food and an illegal wildlife trade.

"We've raised concerns for years about primates being in peril, but now we have solid data to show the situation is far more severe than we imagined," said Russell A. Mittermeier, president of Conservation International (CI) and the longtime chairman of the IUCN Species Survival Commission's Primate Specialist Group. "Tropical forest destruction has always been the main cause, but now it appears that hunting is just as serious a threat in some areas, even where the habitat is still quite intact. In many places, primates are quite literally being eaten to extinction."

The review funded by CI, the Margot Marsh Biodiversity Foundation, Disney's Animal Kingdom and the IUCN is part of an unprecedented examination of the state of the world's mammals to be released at the 4th IUCN World Conservation Congress in Barcelona in October.

With the input of hundreds of experts worldwide, the primate review provides scientific data to show the severe threats facing animals that share virtually all DNA with humans. In both Vietnam and Cambodia, approximately 90 percent of primate species are considered at risk of extinction. Populations of gibbons, leaf monkeys, langurs and other species have dwindled due to rampant habitat loss exacerbated by hunting for food and to supply the wildlife trade in traditional Chinese medicine and pets.

"What is happening in Southeast Asia is terrifying," said Jean-Christophe Vié, Deputy Head of the IUCN Species Program. "To have a group of animals under such a high level of threat is, quite frankly, unlike anything we have recorded among any other group of species to date."

Elsewhere, species from tiny mouse lemurs to massive mountain gorillas face challenges to survive. In Africa, 11 of the 13 kinds of red colobus monkeys assessed were listed as Critically Endangered or Endangered. Two may already be extinct: Bouvier's red colobus (Procolobus pennantii bouvieri) has not been seen in 25 years, and no living Miss Waldron's red colobus (Procolobus badius waldroni) has been seen by a primatologist since 1978, despite occasional reports that some still survive.

"Among the African species, the great apes such as gorillas and bonobos have always tended to grab the limelight, and even though they are deeply threatened, it is smaller primates such as the red colobus that could die out first," said IPS President Richard Wrangham.

As our closest relatives, nonhuman primates are important to the health of their surrounding ecosystems. Through the dispersal of seeds and other interactions with their environments, primates help support a wide range of plant and animal life in the world's tropical forests. Healthy forests provide vital resources for local human populations, and also absorb and store carbon dioxide that causes climate change.

Meanwhile, scientists continue to learn more about primates and their role in the world. Since 2000, 53 species of primates previously unknown to science have been described – 40 from Madagascar, two from Africa, three from Asia and eight from Central and South America. In 2007, researchers found a long-rumored population of Critically Endangered greater bamboo lemurs (Prolemur simus) in a wetland 400 kilometers (240 miles) from the only other known home of the species. In total, the species numbers about 140 individuals in the wild.

The IUCN Red List sets a series of criteria for a species to be categorized as threatened. In cases lacking the necessary information, the species can be listed as Data Deficient, which applied to nearly 15 percent of the primates in the new review. Many of those species, particularly newly discovered ones, are expected to eventually be classified as threatened.

Despite the gloomy assessment, conservationists point to a notable success in helping targeted species recover. In Brazil, the black lion tamarin (Leontopithecus chrysopygus) was downlisted to Endangered from Critically Endangered, as was the golden lion tamarin (Leontopithecus rosalia) in 2003, as a result of three decades of conservation efforts involving numerous institutions. Populations of both animals are now well-protected but remain very small, causing an urgent need for reforestation to provide new habitat for their long-term survival.

"If you have forests, you can save primates," said CI scientist Anthony Rylands, the deputy chair of the IUCN Primate Specialist Group. "The work with lion tamarins shows that conserving forest fragments and reforesting to create corridors that connect them is not only vital for primates, but offers the multiple benefits of maintaining healthy ecosystems and water supplies while reducing greenhouse gas emissions that cause climate change."

Researchers also considered reclassifying the mountain gorilla (Gorilla beringei beringei) to Endangered from Critically Endangered due to increasing populations in their only habitat – the protected mountain jungles of Rwanda, Uganda and Democratic Republic of Congo. However, the slayings of eight mountain gorillas in 2007 and continuing political turmoil in the region delayed the planned reclassification.

ScienceDaily (Aug. 2, 2008) — Just three years after it was discovered, a new species of monkey is threatened with extinction according to the Wildlife Conservation Society, which recently published the first-ever census of the endangered primate. Known as the "kipunji," the large, forest-dwelling primate hovers at 1,117 individuals, according to a study released in the July issue of the journal Oryx.

The population estimate was the result of more than 2,800 hours of field work by WCS scientists in the Southern Highlands and Udzungwa Mountains in Tanzania where the kipunji was discovered. The team found that the monkey's range is restricted to just 6.82 square miles (17.69 square kilometers) of forest in two isolated regions.

The authors also discovered that much of the monkey's remaining habitat is severely degraded by illegal logging and land conversion. In addition, the monkey itself is the target of poachers. Because of these combined threats, WCS proposes that the kipunji should be classified by the World Conservation Union (IUCN) as "critically endangered" – which means it is threatened with extinction in the wild if immediate conservation action is not taken.

"The kipunji is hanging on by the thinnest of threads," said Dr. Tim Davenport, Tanzania Country Director for the Wildlife Conservation Society. "We must do all we can to safeguard this extremely rare and little understood species while there is still time."

Along with the IUCN designation, WCS is investing in the protection and restoration of the kipunji's remaining habitat and local conservation education of local people to help safeguard remaining populations.

The kipunji first made headlines in 2005 when a team of scientists led by WCS announced its discovery. Then in 2006, the monkey made news again when DNA analysis revealed that the species represented an entire new genus of primate—the first since 1923.

ScienceDaily (Aug. 1, 2008) — African elephants are being slaughtered for their ivory at a pace unseen since an international ban on the ivory trade took effect in 1989. But the public outcry that resulted in that ban is absent today, and a University of Washington conservation biologist contends it is because the public seems to be unaware of the giant mammals' plight.

The elephant death rate from poaching throughout Africa is about 8 percent a year based on recent studies, which is actually higher than the 7.4 percent annual death rate that led to the international ivory trade ban nearly 20 years ago, said Samuel Wasser, a UW biology professor.

But the poaching death rate in the late 1980s was based on a population that numbered more than 1 million. Today the total African elephant population is less than 470,000.

"If the trend continues, there won't be any elephants except in fenced areas with a lot of enforcement to protect them," said Wasser.

He is lead author of a paper in the August issue of Conservation Biology that contends elephants are on a course that could mean most remaining large groups will be extinct by 2020 unless renewed public pressure brings about heightened enforcement.

Co-authors are William Clark of the Interpol Working Group on Wildlife Crime and the Israel Nature and Parks Authority, Ofir Drori of the Last Great Ape Organization in Cameroon, Emily Kisamo of the Lusaka Agreement Task Force in Kenya, Celia Mailand of the UW, Benezeth Mutayoba of Sokoine University in Tanzania and Matthew Stephens of the University of Chicago.

Wasser's laboratory has developed DNA tools that can determine which elephant population ivory came from. That is important because often poachers attack elephants in one country but ship the contraband ivory from an adjacent nation to throw off law enforcement.

For instance, 6.5 tons of ivory seized in Singapore in 2002 were shipped from Malawi, but DNA tracking showed the ivory came originally from an area centered on Zambia. Similarly, a 2006 shipment of 3.9 tons seized in Hong Kong had been sent from Cameroon, but DNA forensics showed it came from an area centered on Gabon.

Evidence gathered from recent major ivory seizures shows conclusively that the ivory is not coming from a broad geographic area but rather that hunters are targeting specific herds. With such information, Wasser said, authorities can beef up enforcement efforts and focus them in specific areas where poaching is known to occur as a means of preventing elephants from being killed. But that will only happen if there is sufficient public pressure to marshal funding for a much larger international effort to halt the poaching.

In 1989, most international ivory trade was banned by the Convention on International Trade in Endangered Species of Wild Fauna and Flora, which regulates trade in threatened and endangered species. The restrictions banned ivory trade except for ivory from elephants that nations legally culled from their herds or those that died naturally.

At the time the treaty was enacted, poachers were killing an average of 70,000 elephants a year. The ban instigated much stronger enforcement efforts, nearly halting poaching almost immediately. However, that sense of success resulted in waning enforcement. Western aid was withdrawn four years after the ban was enacted and poaching gradually increased to the current alarming rates, Wasser said.

"The situation is worse than ever before and the public is unaware," he said, "It's very serious because elephants are an incredibly important species. They keep habitats open so other species that depend on such ecosystems can use them. Without elephants, there will be major habitat changes, with negative effects on the many species that depend on the lost habitat.

"Elephants also are a major part of ecotourism, which is an important source of hard currency for many African countries."

The illegal ivory trade is being carried out mostly by large crime syndicates, Wasser believes, and is being driven by growing markets in China and Japan, where ivory is in demand for carvings and signature stamps called hankos.

In addition, in the last few years demand has risen sharply in the United States, where much of the ivory is used to make knife handles and gun grips. In fact, a May report from the Care for the Wild International, a not-for-profit British natural protection organization, ranks the U.S. second behind China as a marketplace for illegal ivory.

But the illegal ivory trade has gotten relatively low priority from prosecutors, and new laws promoting global trade have created "a policing nightmare," Wasser says, which makes ivory poaching a high-profit, low-risk endeavor.

The only way to curb the trade, he believes, is to focus enforcement in areas where the ivory comes from in the first place, before it enters the complex, global crime trade network. Public support is crucial to helping reduce demand and to spur the needed enforcement help from the West.

However, Wasser believes that news reports about the need to cull excess elephants from managed populations in three or four countries have led many people to believe incorrectly that there are too many elephants in Africa. Those managed populations are confined by fences that limit the elephants' natural movements.

"Public support stopped the illegal ivory trade back in 1989 and can do so again," Wasser said. "The work with DNA sampling allows us to focus law enforcement on poaching hot spots.

"It forces countries to take more responsibility for what goes on within their borders, and it also gives us more insight on where to look so that, hopefully, we can stop the poachers before the elephants are actually killed."

The work was funded by the U.S. Fish and Wildlife Service African Elephant Conservation Fund, the University of Washington Center for Conservation Biology and the International Fund for Animal Welfare.

HOUSTON - A "dead zone" in the Gulf of Mexico off the Texas-Louisiana coast this year is likely to be the biggest ever and last longer than ever before, with marine life affected for hundreds of miles, a scientist warned.

"It's definitely the worst we've seen in the last five years," said Steve DiMarco, a Texas A&M University professor of oceanography who for 16 years has studied the Gulf of Mexico dead zone, so named because the oxygen-depleted water can kill marine life.

The phenomenon is caused when salt water loses large amounts of oxygen, a condition known as hypoxia that is typically associated with an area off the Louisiana coast at the mouth of the Mississippi River. The fresh water and salt water don't mix well, keeping oxygen from filtering through to the sea bottom, which causes problems for fish, shrimp, crabs and clams.

This year's dead zone has been aggravated by flood runoff from heavy spring rains and additional runoff moving into the Gulf from record floods along the Mississippi.

DiMarco, joined by researchers from Texas A&M and the University of Georgia, just returned from an examination of 74 sites between Terrebonne and Cameron, La. He said the most severe hypoxia levels were recorded in the mid-range depths, between 20 and 30 feet, as well as near the bottom of the sea floor at about 60 feet.

Some of the worst hypoxic levels occurred in the western Gulf toward the state line.

"We saw quite a few areas that had little or no oxygen at all at that site," DiMarco said Tuesday. "This dead zone area is the strongest we've seen since 2004, and it's very likely the worst may be still to come.

"Since most of the water from the Midwest is still making its way down to the Gulf, we believe that wide area of hypoxia will persist through August and likely until September, when it normally ends."

Last year, DiMarco discovered a similar dead zone off the Texas coast where the rain-swollen Brazos River emptied into the Gulf.

The zone off Louisiana reached a record 7,900 square miles in 2002. A recent estimate from the National Oceanic and Atmospheric Administration and Louisiana State University shows the zone, which has been monitored for about 25 years, could exceed 8,800 square miles this year, an area roughly the size of New Jersey.

DiMarco said a tropical storm or hurricane likely would have no impact on this year's zone, believed to be caused by nutrient pollution from fertilizers that empty into rivers and eventually reach the Gulf.