Killer Dolphins

The plump, four-foot-long harbor porpoises that inhabit Moray Firth on the northeast coast of Scotland have been under attack for years. Most carcasses that wash up on Scottish beaches show signs of the same mysterious--and violent--cause of death: fractured ribs and shattered vertebrae, apparently the result of high-energy impacts. There are also other wounds--deep tears in the blubber and evenly spaced, parallel scratches on the skin. Zoologist Ben Wilson and a team of researchers at the University of Aberdeen and the Scottish Agricultural College Veterinary Services in Inverness have identified an unlikely killer: the bottle-nosed dolphin, popularly assumed to be gentle and playful. Wilson and his colleagues found that the scratches on the dead porpoises match the peglike teeth of the bottle-nosed dolphin. The dolphins may be competing with harbor porpoises for food, practicing tactics for fighting one another, or merely responding to the stress of living at the northern-most limit of their range. It could also be good fun for the dolphins, says Wilson. The surprising thing is that people haven’t seen this elsewhere where the two species coexist.