Sea wolves

FOR decades, rangers in Yellowstone National Park, in the American West, had to cull the area’s red deer (known locally as elk, though they bear no resemblance to European elk, known locally as moose) because the animals’ numbers were grazing the place to death and thus threatening the livelihoods of other species. Many ecologists argued that the deer had once been kept under control by wolves, which had been hunted to extinction by people. When wolves were reintroduced to Yellowstone, in 1995, these arguments proved correct. The deer population fell to manageable levels, and culling stopped. Wolves, it turned out, played a crucial role in keeping the wider ecosystem intact. Now comes evidence that the same is true for another top predator: sharks.