On the surface, plummeting populations of sharks do not seem like much cause for concern for humans or, for that matter, other sea life. But this simple viewpoint relies on splitting animals into two groups – predators and prey. In practice, this distinction is far too crude. Too put it bluntly, there are predators and there are predators. Those at the top kill those in the middle, and stop them in turn, from killing those at the bottom. As the old saying goes, the enemy of my enemy is my friend.
The rise in shark fishing is mainly driven by a growing market for their fins. Shark fins soup is a delicacy in China, which is utterly ludicrous given that the fins themselves are tasteless and merely add texture. China’s strong economy has put this expensive treat in the range of the expanding middle classes and the world’s sharks are paying the price for it.
Ransom Myers from Dalhousie University, Halifax, decided to study the effects of declining shark numbers by analysing a uniquely comprehensive shark census taken over the last 30 years on the American eastern seaboard. In these waters, several shark species have all but vanished since 1972, including 99% of the bull, dusky and smooth hammerhead populations. And because fishing expeditions tend to catch larger individuals, the average size of the survivors has plummeted. Mighty animals like the tiger and black-tip sharks are now up to half as long as they used to be.
Unsuprisingly, as the sharks declined, their prey benefited. Great sharks mainly hunt smaller predators, including their close relatives skates, rays, and indeed, smaller sharks, whose numbers surged in their absence. The cownose ray, for example, is now ten times more common than it was in the mid-70s. And here’s where the domino effects begin.