Cascading Effects

Fishermen in North Carolina correctly inferred a connection between diminishing shellfish catches and exploding numbers of cownose rays, which turn out to be voracious consumers of scallops and clams. But what explained the booming ray population? Just keep going up the food chain. As Ransom Myers and colleagues found, the great sharks, which prey on rays and other 'meso-predators', have seen their populations crash precipitously in recent decades, to the point where they are no longer a major ecological force. That's not only bad news for bi-valves and those who love them, but also a prime illustration of how the impacts of overfishing can trickle down through the food chain in what scientists call a "trophic cascade."