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  Yahoo News 30 Mar 07
Over-fishing of Atlantic sharks upsets ecosystem balance: study

Yahoo News 30 Mar 07
Shark deaths endanger scallop population
By Randolph E. Schmid, AP Science Writer

National Geographic 29 Mar 07
Shark Declines Threaten Shellfish Stocks, Study Says
Helen Scales

Yahoo News 29 Mar 07
Alarming Decline of Sharks Causing Other Species to Vanish
Andrea Thompson LiveScience

PlanetArk 30 Mar 07
Overfishing of Sharks Makes Scallops Vanish - Study
Story by Deborah Zabarenko, Environment Correspondent

WASHINGTON - Overfishing of big sharks in the Atlantic has cut stocks by 99 percent, dooming North Carolina's bay scallop fishery and threatening other species including shrimp and crabs, researchers reported on Thursday.

With most of the great predatory sharks -- bull, great white, dusky and hammerhead -- gone from northwest Atlantic waters, the rays and skates the sharks normally feed on had a population explosion, the scientists said in the journal Science.

"With fewer sharks around, the species they prey upon -- like cownose rays -- have increased in numbers, and in turn, hordes of cownose rays dining on bay scallops have wiped the scallops out," said study co-author Julia Baum of Dalhousie University in Halifax, Nova Scotia.

Bull, dusky and hammerhead sharks have declined by more than 99 percent between 1970 and 2005, Baum said in a statement.

This coincided with a rise in Asian demand for shark fins for medicinal uses and for food. Shark fins currently sell for about US$22 a pound, Peterson said, citing a local fisherman.

Now that the ravenous rays and skates have feasted on bay scallops, they are likely to look for food in protected areas along the coast where other fish and shellfish shelter in their early months of life, said co-author Charles "Pete" Peterson of the University of North Carolina at Chapel Hill.

"We know that once they eat the things that are the most easy, evident and obvious to get, which are those on the surface of the bottom like a scallop and an oyster, they turn to digging in the bottom to get buried shellfish," Peterson said by telephone.


Rays and skates are good diggers and can excavate seagrass beds along the Atlantic coast, Peterson said.

Seagrass beds are normally used as nurseries for young fish and shellfish like shrimp and crabs because they protect against predation by what Peterson called "wimpier predators" such as crabs; they are not build to stand up to raids by bigger species like rays.

"It's a nice hiding place and a productive habitat," Peterson said of the seagrass beds. "It tends to be warmer and less violent physically. ... You probably don't have nannies, but outside of that, you've got everything you'd want in a nursery in the seagrass bed."

Many Atlantic coast and Gulf of Mexico fisheries are dominated by animals and plants that depend on estuaries, the parts of rivers that connect to the sea.

If rays and skates prey on these shellfish and some of the young grouper and snapper fish that begin their lives in the seagrass, these species could also be threatened, Peterson said.

The overfishing of sharks may be a consequence of a previous overfishing of cod, Peterson said. When fishing agencies looked for an unexploited resource to replace cod as a mainstay, they settled on shark about 25 years ago.

Sharks, in huge demand in Asia, are also frequently caught inadvertently by nets meant to snare swordfish, he said.

Yahoo News 30 Mar 07
Over-fishing of Atlantic sharks upsets ecosystem balance: study

The virtual elimination of large sharks from coastal waters off the US eastern seaboard has disturbed the marine ecosystem, and wiped out one US bay scallop fishery, a study released Thursday said.

The massive over-fishing of the largest predatory sharks in the coastal waters of the Atlantic over the past 30-some years has led to an explosion in the ray, skate and small shark species that they prey on, with devastating effects for one of the organisms at the bottom of the food chain.

"Large sharks have been functionally eliminated from the east coast of the US, meaning that they can no longer perform their ecosystem role as top predators," said Julia Baum, a doctoral student at Dalhousie University in Halifax, Canada and co-author of the paper.

"With fewer sharks around, the species they prey upon -- like cownose rays -- have increased in numbers, and in turn, hordes of cownose rays dining on bay scallops have wiped the scallops out."

Several of the larger shark species in the northwest Atlantic are verging on extinction, according to Baum and colleagues who analyzed a dozen surveys dating from 1970 up to 2005. The numbers of scalloped hammerhead and tiger sharks appear to have declined by more than 97 percent over that period, while populations of bull, dusky and smooth hammerhead sharks could be down as much as 99 percent, according to this analysis.

The reasons are not hard to find, say the marine biologists. The growing demand for shark fins and shark meat, particularly in Asia, has led to a rapid escalation in shark-fishing.

With the drop in shark population, a dozen species of rays, skates and small sharks have increased in numbers over the past 16 to 35 years, some of them tenfold, according to other data reviewed by the marine biologists. Perhaps the most conspicuous beneficiary of the decline in shark numbers is the east coast cownose ray, whose numbers have exploded, rising an average of eight percent a year to bring the total population to an estimated 40 million, according to the study in the journal Science.

The rays feed on mollusks including bay scallops, oysters, and soft-shell and hard clams.

The boom in cownose ray numbers has been nothing short of a disaster for North Carolina's bay scallop fishermen. In the early 1980s, researchers who sampled the bay scallops in the North Carolina sounds before and after the rays' annual summer feeding session, found their numbers were sufficient to sustain a commercial fishery and still replenish themselves every year.

By 1996, the migrating rays were consuming nearly all of the scallops in the area by early fall, except those protected by fences the researchers had put up to keep the rays out. By 2004, the fishermen who harvested the scallops had gone out of business, ending a century-old North Carolina tradition.

"This is just a small window into this domino effect," said Charles Peterson, a professor at the Institute of Marine Sciences, University of North Carolina at Chapel Hill and co-leader of the study.

The effects on the ecosystem of increases in the other rays, skate and smaller shark species is still unclear, but there may be a cascade effect there too, the authors of the paper said.

"Our study provides evidence that the loss of great sharks triggers changes that cascade throughout coastal food webs," said Baum. "Solutions include enhancing protection of great sharks by substantially reducing fish pressure on all of these species and enforcing bans on shark finning both in national waters and on the high seas."

Yahoo News 30 Mar 07
Shark deaths endanger scallop population
By Randolph E. Schmid, AP Science Writer

Overfishing of powerful sharks — a top predator in the ocean — may endanger bay scallops, a gourmet delicacy. With fewer sharks to devour them, skates and rays have increased sharply along the East Coast and they are gobbling up shellfish, particularly bay scallops, researchers report in Friday's issue of the journal Science.

Ecologists have known that reducing key species on land can affect an entire ecosystem, but this study provides hard data for the same thing in the ocean, said lead author Charles H. Peterson of the Institute of Marine Sciences at the University of North Carolina. Co-author Ransom A. Myers of Dalhousie University in Halifax, Nova Scotia, and Peterson were studying different ends of the food chain, Peterson said in a telephone interview.

"Myers was working on great sharks and I was working on cownose rays and their impact on bay scallops and other shellfish. We realized that separately we had interesting science, but together we had an absolute revelation," he said.

"We were able to show why these top predators matter," Peterson said. "We knew the answer right there, that there was a consequence." Peterson, who works at the university center in Morehead City, N.C., said scallops used to be so abundant there that people were allowed to collect a bushel a day.

"The kids were able to see that food doesn't just come from a market," he said. Now, scallops are very reduced, he said.

"The rays, as they come through, eat all that are in any dense patch and have eaten so many there does not appear to be enough to create spawning stock."

Scallops are an easy target because they do not burrow into the sand, Peterson said.

Millions of rays from Chesapeake Bay migrate through the area, he said. "What are they going to feed on to fuel their migration?"

In some areas they enter seagrass beds and dig up clams, but that is an important nursery habitat for shrimp, blue crabs and fish, Peterson said, "so there is a high concern that we may now be cascading to habitat destruction."

Not so sure was Steve Murawski, director of scientific programs at the National Marine Fisheries Service. He said the links between the large sharks, medium size rays and bay scallops were "tenuous." There is very little food and feeding data on the rays, he said, and in terms of the decline of bay scallops, habitat degradation and environmental issues could be factors, too.

As for the increase in rays, he said, they used to be widely caught and discarded and fishing has declined in their prime habitat.

Murawski, who was not part of the research team, said he is not saying there is no relationship among the sharks, rays and scallops, only that other factors also need to be considered.

Robert E. Hueter, director of shark research at Mote Marine Laboratory in Sarasota, Fla., said scientists have warned about the effects of shark depletion for years but there have been few studies to back them up.

This report, he said, "demonstrates plausible links between the decline of sharks, the subsequent rise of their prey, and the resulting decline of those prey species' prey. You don't have to be a marine biologist to grasp this connection."

"Scientists will now debate the specific numbers and correlations in this paper, and sadly, Dr. Myers will not be around for that debate," he said. Myers, 54, died Tuesday in Halifax.

Hueter, who was not part of the research team, said the "overall message is important and true: If we take out whole segments of ecosystems, especially top predators like sharks, the balance among species is toppled, and the effects cascade throughout the system. And some of those effects — such as a negative impact on other important fisheries, as in the Myers study — can be long-term and deleterious to human society."

Ellen Pikitch, executive director of the Pew Institute for Ocean Science, said scientists have known that the loss of the great sharks would ripple through the ecosystem in some way, but this is "the first study to show consequences with hard data."

Pikitch was not part of the research team, but the Pew Institute helped support the work. Other funding came from the Sloan Census of Marine Life, Natural Sciences and Engineering Research Council of Canada, Killam Trust, North Carolina Fisheries Resource Grants Program, North Carolina Sea Grant and the National Science Foundation. ___

Yahoo News 29 Mar 07
Alarming Decline of Sharks Causing Other Species to Vanish
Andrea Thompson LiveScience

The precipitous decline in large predator sharks in the Atlantic Ocean in the past decade has made ecologists worry about a trickle-down effect on the ocean ecosystem.

A new study supports the case. With the large predators gone, their prey—smaller sharks and rays—are free to feast on lower organisms like scallops and clams, depleting valuable commercial stocks.

“Large sharks have been functionally eliminated from the East Coast of the U.S., meaning that they can no longer perform their ecosystem role as top predators,” said study team member Julia Baum of Dalhousie University in Halifax, Nova Scotia.

Disappearing sharks

Shark populations all over the world have plummeted because of intentional fishing for their fins, which are eaten and used for medicines in Asia, and "bycatch," in whicn sharks are accidentally caught when fisherman target other species.

For this study, published in the March 30 issue of the journal Science, the researchers looked at surveys of populations of 11 great shark species, conducted between 1970 and 2005.

Every species had substantially declined in just those few decades. The smallest observed decline was in sandbar shark populations, which had decreased nonetheless by 87 percent. Other species, including the bull, dusky and smooth hammerhead sharks, may have declined by more than 99 percent.

“They’re all down dramatically,” said study co-leader Charles Peterson of the University of North Carolina. Two of the shark species studied have been Endangered Species Act candidates since 1997, but have yet to be added to the list, Baum said.

Domino effect

When one predator disappears from an ecosystem, others that eat the same prey usually take over and keep the balance of the ecosystem in check.

But in this case, where not one, but all, of the top predators are rapidly disappearing, “you lose the resiliency and buffering capacity of one species to step in for another,” Peterson told LiveScience.

The loss of top predators has a domino effect on the rest of the ecosystem; populations of lower-level predators, such as rays, skates and smaller sharks, aren’t kept in check, allowing them to overeat and wipe out their own prey.

The study looked in particular at cownose rays, which feed on bay scallops along the east coast as they migrate in the autumn. In a 1983–84 study, Peterson found that as the cownose rays came through, they “didn’t make a dent on the scallops.”

But when the researchers repeated the study from 2003—04, “the scallops were essentially eliminated,” he said. The only scallops that were spared were those that were protected by poles erected by the researchers to keep out the rays, which are broader than the space between the poles.

More repurcussions

Peterson said that the U.S. National Marine Fisheries Service is aware of the problem of declining shark populations and has taken some steps to mitigate the problem, but he emphasized the need to manage whole ecosystems rather than specific species.

In the meantime, Peterson said the problem may be far greater than this study shows: other intermediate predators could be destroying other lower organisms, such as clams and oysters, which are also valuable commercial stocks.

“We haven’t even scratched the surface,” he said.

National Geographic 29 Mar 07
Shark Declines Threaten Shellfish Stocks, Study Says
Helen Scales for National Geographic News

Dramatic declines of large North Atlantic sharks due to overfishing have upset the balance of entire marine ecosystems, a new study shows. Now scallops, clams, and oysters are paying the price.

Smaller sharks, skates, and rays that are normally eaten by the large sharks have become so abundant that they are ravaging shellfish stocks, the researchers say.

The shark declines, fed by growing worldwide demand for shark-fin soup, are indirectly causing some scallop fisheries to collapse entirely, the scientists add.

The study, which appears in this week's issue of the journal Science, is the first ever demonstration of how wiping out top-level predators causes impacts that cascade down through the rest of the food web, the study authors say.

"Industrial fishing has left so few big sharks that they no longer perform their role as the top predators," said study co-author Julia Baum of Dalhousie University in Nova Scotia. "The predators of smaller species of sharks and rays have been virtually wiped out."

Wholesale Declines

A 2003 study by Baum and fellow Dalhousie biologist Ransom Myers used fisheries' logbooks to track severe declines in large sharks since the 1980s.

In the new research, Myers, Baum, and three other marine biologists compiled additional fisheries' records and independent research surveys going back to the 1970s to reveal that the original study underestimated the declines.

"This time we saw some species declining by 99 percent and more," said co-author Charles Peterson, a biologist at the University of North Carolina (UNC).

What was most alarming was that all 11 major species of predatory shark--including sandbar, blacktip, tiger, hammerhead, and bull sharks--drastically declined, Peterson said.

"As a consequence we can explain why 12 of their 14 prey shark and rays species shot up in abundance in the same time frame," he added.

One species to benefit from the shark declines is the cownose ray, which has increased 20-fold in the last 30 years to around 40 million individuals. But the shellfish they feed on have been suffering.

"Twenty years ago the abundance of rays was not sufficient to make a dent in the population of scallops," said UNC's Peterson, who has studied bay scallops in North Carolina since the 1980s.

"With the arrival of more rays, the scallop populations became decimated, and the [area's] century-old fishery has closed," he said. "By excluding rays from small areas using underwater stockades, we showed that scallop populations do fine when they can escape the foraging rays."

The new shark study "is an excellent illustration of the keystone importance of big sharks for marine ecosystems," said Sarah Fowler, co-chair of the World Conservation Union's (IUCN) Shark Specialist Group.

"Big sharks are likely to be an important and beneficial influence not only on scallop stocks, but also for other commercially important species in the food web that we haven't yet considered," she added.

For example, one worry is the impact cownose rays might have if they shift their diet to other species.

"Herds of rays may destroy seagrass beds as they go through looking for smaller buried mollusks," Baum, of Dalhousie University, said. "Our concerns are now that the cascade is going to continue one step further and threaten crucial nursery habitats for many marine species."

Worrying New Plans

Eager to turn disaster into profit, U.S. entrepreneurs are now moving to establish cownose ray fisheries and promote new markets. That's exactly the same situation as the early 1980s, when other sharks were regarded as an underutilized resource, Baum said.

But just two decades later there's a very real possibility of their extinction of the Northwest Atlantic. "It would be a huge mistake to think that people can rush in and fish cownose rays without taking into account how vulnerable they are."

Cownose rays take seven years to mature, and females give birth to only one pup a year. Furthermore, IUCN's Fowler added, "recovery of the predatory sharks will not happen if some of their most important prey--the rays--have also been depleted."

"This study," Baum noted, "underlines the need to consider ecosystems as a whole."

Related articles on Global: marine issues, Shark's fins and seagrasses
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