Richard Collins: Why would whales kill porpoises they don't eat?

"...the Southern Resident Group of killer whales in the Pacific has only 78 members - attacks on porpoises by these whales were dismissed as one-off freak occurrences. Since then, however, 78 such incidents have been documented..."

A harbor porpoise calf being balanced out of the water. The porpoise eventually swam away, and its survival outcome was unknown. Picture: Candice Emmons, taken under NOAA permit #21348

Killer whales, despite their name, are relatively benign creatures, which only target their victims for food. Recently, however, the gentle giants were ‘outed’ — they have been blotting their copy-books.

In 1991, at a marine park near Victoria in Canada, trainer Keltie Byrne entered a pool which had two female killer whales and a male. It was the first time she had been in the water with them. The females seized Keltie, tossing her back and forth between them. The male, named Tilikum, joined in. The unfortunate trainer drowned.