The Office of
307 Bynum Hall
Campus Box 4106
UNC-Chapel Hill
Chapel Hill, NC 27599-4106
Tel: (919) 962-6136
Chief Brody was wrong: we don’t need a bigger boat. We need more sharks.
Because we’ve overfished these ancient predators, booming populations of the prey they would normally eat are upsetting the ocean’s ecological balance, said Charles Peterson, co-author of a new study on overfishing. North Carolina’s bay scallop fishery, which thrived for almost a century, is now dead in the water. Rays and skates ate almost all the scallops.
This happened because we’re killing the biggest and baddest sharks as fast as we can pull them out of the water. By using data from thirty-five years of shark surveys conducted by Frank Schwartz of UNC’s Institute of Marine Sciences, Peterson and his co-authors found that there are now 97 percent fewer tiger sharks and scalloped hammerheads off the North Carolina coast than there were 20 years ago. There are 99 percent fewer smooth hammerheads and bull sharks now than there were then. And those that are left aren’t growing as large as their predecessors did.
People sometimes yank them aboard, cut off their fins, then throw the sharks back to drown or be eaten alive. Peterson says most North Carolina fishermen bring the whole shark back to the dock, as the law specifies — but that’s still the end of the line for the shark. Still other fishermen looking for tuna or swordfish get sharks instead — sharks that would otherwise be eating skates and rays. When the sharks are away, the rays will prey.
About 25 years ago, Peterson checked bay scallop populations in North Carolina sounds both before and after the cownose rays migrated through. He found that the grazing rays left enough scallops to replenish scallop populations and to support a fairly healthy scallop fishing trade.
Fast-forward to the early 2000s, with big sharks on the wane and cownose ray populations exploding. This time, Peterson and his colleagues found that the rays ate almost all the adult bay scallops. In fact, most of the scallops they didn’t eat were those inside special fences Peterson had built to keep the rays out.
So, what’s the big deal? Can’t we just get our scallops somewhere else?
Problem is, all those rays and skates are still hungry. They’re going to be looking for food wherever they can get it — including in protected “nursery” areas along the coast where other immature fish and shellfish hide out and grow up. “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. If the rays start raiding fish nurseries, they could wreak similar havoc on many other species.
And we could be looking at a ripple effect much more sinister than the surge of a great white’s dorsal fin. “Maintaining the populations of top predators is critical for sustaining healthy oceanic ecosystems,” Peterson said. “Despite the vastness of the oceans, its organisms are interconnected, meaning that changes at one level have implications several steps removed.
“The great sharks play a role in structuring the entire ocean ecosystem. In their absence, dramatic ecosystem reorganization occurs, threatening many goods and services historically delivered by the sea.”
And if the economic arguments aren’t persuasive, think about this: We’re talking about beasts that have, in one form or another, seen the dinosaurs come and go. They have weathered anywhere from 450 million to 100 million years of whatever the rest of the planet could throw at them. And now we’re wiping them out because some people like to eat soup made from their fins.
If you’d like to help save our sharks, Peterson said, take the time to send your comments and concerns to NOAA’s National Marine Fisheries Service. “Public advocacy and comment is welcome and has power,” Peterson said.
And if you catch a shark, release it.
Charles Peterson is Distinguished Professor of Marine Sciences. This research was published in the March 30, 2007 issue of Science and was supported by the Pew Global Shark Assessment, the Killam Trusts, the Natural Sciences and Engineering Research Council of Canada, the North Carolina Fisheries Resource Grants Program, the UNC Institute of Marine Sciences, the Sloan Census of Marine Life, and the National Science Foundation. Contact NOAA’s National Marine Fisheries Service online at www.nmfs.noaa.gov.
Editor: Neil Caudle
Writer: Jason Smith