Media Contact: Lisa Young
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Despite battling a public relations image
that has elevated them to tabloid status, sharks play a vital role in
the ocean’s food chain. Fewer big sharks in the oceans mean that bay
scallops and other shellfish may be harder to find at the market,
according to an article in the March 30 issue of the journal Science,
tying two unlikely links in the food web to the same fate.
A team of Canadian and American ecologists, led by world-renowned
fisheries biologist Ransom Myers at Dalhousie University, has found that
overfishing the largest predatory sharks, such as the bull, great white,
dusky, and hammerhead sharks, along the Atlantic Coast of the United
States has led to an explosion of their ray, skate, and small shark prey
species.
“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,” says co-author
Julia Baum of Dalhousie.
Co-author Dr. Sean Powers, a Senior Marine Scientist at the Dauphin
Island Sea Lab and Assistant Professor of Marine Sciences, University of
South Alabama, says, ““Shark populations are uniquely susceptible to
over-fishing. Compared to other fish, sharks have very low reproductive
rates and are extremely long-lived.”
Here on the Gulf Coast, Dr. Powers and DISL Marine Scientist Dr. John
Dindo are in the midst of a long-term survey of Alabama coastal shark
populations. In monthly trips to depths of four-to-sixty feet, the
scientists and their teams long-line sharks for tagging, as well as
collecting tissue samples and determining the health and age of the
sharks. With 80 species of sharks in the Gulf of Mexico, twenty-nine of
them coastal species, Drs. Powers and Dindo are collecting invaluable
data to help determine the status of sharks in the Gulf.
“By conducting a long-term study of the shark population along the
Alabama Gulf Coast we’re trying to determine how their populations have
and will change over time and what does the future hold for them.‘
“In the Atlantic, the removal of these top predators led to the collapse
of the century-old scallop fishery in North Carolina. We need to find
out if we see the same changes in the Gulf of Mexico and evaluate the
potential impact of these changes on shellfish populations.’
“The cownose ray example is just one of a growing number of studies that
point out that fishery species are connected throughout the foodweb and
that management of one species can have consequences for others.
Consequently, efforts to manage fisheries need to take into account
these multi-species or ecosystem effects,” he concludes.
“Sharks have received a bad rap,” says Dr. Dindo. “People may shrug
their shoulders when they hear that their populations are at risk, but
perhaps they’ll pay more attention when they realize that without these
predators, it’ll be harder to obtain oysters, blue crabs and other
species that we value here in the Gulf.”
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