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UP FRONT | SHARKS
Big Atlantic sharks disappearing, study warns
Overfishing of the Atlantic Coast's largest sharks may cause a decline in the population of valuable shellfish, according to a report today in the journal Science.
BY CURTIS MORGAN
cmorgan@MiamiHerald.com
On the Web | This week's 'Science'
Humans, mainly those in countries with a craving for shark-fin soup, have devoured so many of the oceans' top predators that it has rattled the length of the marine food chain, according to a study to be published today in the prestigious journal Science.
While previous studies have calculated declines by half or more, this one argues that seven of the largest sharks along the Atlantic Coast have all but vanished because of overfishing -- down as much as 99 percent for bull, dusky and smooth hammerheads over the last 35 years.
Researchers believe the disappearance triggered a boom-and-bust cycle for other sea life, resulting in the wipeout of a valuable scallop fishery -- a ripple effect biologists have long warned about but that has not been widely documented.
'I am not using the word `extinction' at this point. The ecological term we would use is 'functionally eliminated,' '' said co-author Julia Baum, a biologist at Dalhousie University in Canada. ``It means there aren't enough of these top predators around anymore to do their role.''
The researchers and conservationists cite the study, funded by the Pew Institute for Ocean Science at the University of Miami, as compelling support for shutting down commercial and recreational shark fishing. That would have major implications in Florida, which leads the nation in commercial landings of sharks.
Sonja Fordham, shark conservation coordinator for The Ocean Conservancy, credited federal fishery managers with trying to slow the decline with quotas and limited seasons but said, ``It's been too little, too late.''
'After 13 years of trying, we're in the position of saying, `Game over, it's not working,' '' she said.
Commercial fishing interests were highly skeptical.
''If they're saying the decline is 99 percent in some species, well, they're nuts. They need to go out swimming in some of these areas,'' said Robert Spaeth, executive director of the Southern Offshore Fishing Association in Madeira Beach, which represents long-line boats that take the bulk of the shark catch in Florida.
Federal scientists with the National Marine Fisheries Service, which is reassessing shark fishing regulations, said they already had analyzed much of the same data and questioned the study's conclusions -- both the collapsed shark populations and what scientists call a ''cascade effect'' on other sea life.
Margo Schulze-Haugen, chief of a Fisheries Service branch that oversees sharks, said researchers built their projections from select information, a dozen surveys over 25 years by scientists from Cape Canaveral to Maryland.
''I don't doubt that these are accurate for that survey,'' she said. ``They may be in decline there, but these species are wide-ranging.''
For its part the research team, which includes five biologists from the University of North Carolina at Chapel Hill and Dalhousie in Nova Scotia, argues that federal managers rely too much on counting what winds up on the hooks of commercial skippers, who have grown increasingly efficient at tracking a dwindling quarry with satellite navigation and sonar fish-finders. That data masks an alarming picture, said co-author Pete Peterson, a professor of marine sciences at UNC. This study relied on consistent methods in areas that should maintain healthy populations of sharks.
Ellen Pikitch, a professor at UM's Rosenstiel School of Marine and Atmospheric Science and executive director of the Pew Institute, called such surveys ``the gold standard in terms of quality.''
The unlikely linking of big sharks and small scallops also is an important breakthrough, she said.
''What we have always said is we know that sharks play an important ecosystem role in the oceans . . . and we're likely to see some cascading effects from their decline,'' Pikitch said. ``This is the first paper to show some reciprocal effects.''
The study's premise: As larger sharks disappeared, smaller ones and rays, both often prey, exploded over the same period. One in particular, the cownose ray, perpetuated to the point that by 2004 it gulped down much of the scallop population in Chesapeake Bay.
''I think that's just the tip of an iceberg,'' Fordham said. ``There are so many connections we don't understand. Sharks keep the oceans in balance.''
Steve Murawski, chief science advisor for the Fisheries Service, called the shark-scallop link ''not particularly convincing.'' Stomach-content studies, he said, have shown that small sharks or rays make up less than 3 percent of the diet of large sharks and that cownose rays don't have a big appetite for scallops.
''This study is not based on an examination of who eats who,'' he said, ``It's a correlation of the decline in one stock and the increase in another.''
Scientists say there is no way to count the sharks in the sea, and sports anglers frequently report seeing them. But there is little disagreement that fishing pressure has whacked big sharks hard.
Driven in large part by high prices for fins in Asia, commercial catches surged 50-fold between 1979 and 1989 alone.
Over the past 10 years, the fisheries service has banned anglers from keeping 19 varieties of shark, including the great white and dusky. In the latest assessment in January, it lists the status of 11 coastal sharks in the study as ``unknown.''
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