Sunday 15 October 2000

THE New Zealand sea lion (Phocarctos hookeri) has been exposed as a cannibal, making it the first species of sea lion to be caught eating its own kind.

Scientists who studied the population structure of a breeding colony at Dundas Island were amazed to see 47-stone males grabbing pups which weighed only about two stones, dragging them into the sea and devouring them. As the mothers called plaintively from the shore, the males bit off the pups' limbs and shook their bodies with such ferocity that the carcasses were hurled out of the water.

Cannibalism has been seen among grey seals in Canada and elephant seals in Argentina, but it has never before been recorded among fur seals or sea lions. Dr Ian Wilkinson, the biologist leading the study, said: "We were shocked. The male would come ashore, grab the pup, swim out 50 or 100 metres with it, shake it around, kill it, and then bite off chunks and limbs and eat them.

"When it was happening, we would see whole groups of seabirds gathering nearby. Then all of a sudden, you would see a pup come flying out of the water and watch the carcass splash down. It's never pleasant to see that sort of thing. I don't think anybody enjoys seeing animals kill other animals."

In 12 weeks, the scientists recorded 24 cases of cannibalism at Dundas Island, 200 miles south of New Zealand, where up to 300 pups are born every year. Eleven killings were witnessed during the first study period in early 1999 and a further 13 occurred in January and February this year.

Dr Wilkinson, of the New Zealand Department of Conservation, said: "We saw the male grabbing the pups on two occasions. We saw them eating the pups in a further 22 cases. In one instance we saw the mother bite the male, who dropped the pup and bit her. He was twice or three times her weight. There was nothing she could do. When the male took the pup away, the mother called as she would when returning from a feeding trip. She sat on the rocks calling for about 25 minutes."

The New Zealand (or Hooker's) sea lion, is one of the rarest sea lion species in the world. Dr Wilkinson said the cannibal males could be killing about two per cent of a population of between 13,000 and 17,000. "It is not good for the species as a whole, but maybe it is a clever feeding strategy for the individual males involved. It is very difficult to speculate on why they do it. Maybe it's because the pups are an easy source of food. Normally they might have to swim out and dive to 300 or 400 metres to catch squid. But a single pup is enough to meet their daily needs for food, and they don't have to expend huge amounts of energy to get it."

Although never before witnessed in sea lions, cannibalism is common in many other species, and has been recorded in at least 100 mammals, including man.

Dr Wilkinson said: "There are several reasons for cannibalism. As well as killing for food, adults will kill unrelated young to increase their access to food or breeding sites for themselves and their offspring. A third reason is sexual selection, where males kill unrelated offspring. This is common in lions. When a male takes over a pride, he will often kill all the pups, because the females will then come into season and he can produce offspring of his own."

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