"Increased predation by cownose rays also may inhibit recovery of oysters and clams from the effects of overexploitation, disease, habitat destruction, and pollution, which already have depressed these species," says Peterson, noting shellfish declines in areas occupied by cownose rays and examples of stable or growing shellfish populations in areas beyond the ray's northernmost limit.
Ecosystem effects of increases in the other ray, skate, and smaller shark species are unknown, but like the cownose ray, may also be cascading down to species lower in the food web.
"Despite the difficulty of piecing together ecosystem impacts of overfishing," co-author Travis Shepherd of Dalhousie emphasizes, "the real challenge will be to move beyond retrospective analyses and instead prevent ecosystem-wide changes from happening in the first place."
"Our study provides evidence that the loss of great sharks triggers changes that cascade throughout coastal food webs," says Baum. "Solutions include enhancing protection of great sharks by substantially reducing fishing pressure on all of these species and enforcing bans on shark finning both in national waters and on the high seas."
"Maintaining the populations of top predators is critical for sustaining healthy oceanic ecosystems," says Peterson. "Despite the vastness of the oceans, its organisms are interconnected, meaning that changes at one level have implicatio
Source:University of Miami Rosenstiel School of Marine & Atmospheric Science