Overfishing of one species can result in the decline or rise of others. For example, data suggests that there is a causal link between declining large shark populations and the declining North Carolina bay scallop fishery.

The data suggests that predation of bay scallops has increased, because large sharks have been overfished.  These sharks prey on marine organisms, such as cownose rays, which prey on the bay scallops. As a result of the anthropogenically caused imbalance, rays are becoming too abundant. These rays are blamed for impacting the Chesapeake Bay oyster fishery as well.

Obviously there are other factors preventing the recovery of the clam, oyster, and scallop fisheries. Other factors that have impacted shellfish fisheries include habitat degradation, loss, and fragmentation; and pollution coupled with overfishing are other factors, so predation is just another factor that prevents recovery of these fisheries. However, to protect North Carolina bay scallops, scientists are constructing sanctuaries that rays cannot enter. From The Virginian-Pilot, VA:

Scientists believe that three new sanctuaries in coastal sound waters will protect scallops during the summer onslaught of feeding rays, which have proliferated with the decline of great shark species.

“They range upwards to the size of the infield of a baseball diamond,” UNC Chapel Hill Professor Charles “Pete” Peterson said of the sanctuaries, which are referred to as stockades.

Peterson is part of a team from the school’s Institute of Marine Sciences in Morehead City that worked in recent weeks to build the sanctuaries in the Bogue, Back and Core sounds.

The enclosures, which Peterson said have proved successful in the past, will keep the rays from eating some of the scallops during the spawning season.

They are created by placing PVC pipes vertically in the water close enough together that the rays can’t enter. Peterson said the hope is that enough scallops survive the ray migration that the population can start to rebuild itself.

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The cownose ray has been blamed for nearly finishing off a Chesapeake Bay oyster population already ravaged by disease. The winged marine animal has also taken a heavy toll on North Carolina’s scallop fishery, which has been closed since 2004.

The ray population has grown as the number of great sharks – their predators – has fallen from overfishing, Peterson said.

Peterson co-authored an article published in the journal Science last year. He and fellow marine researchers presented the results of numerous marine studies conducted since the early 1970s.

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