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Planet Earth

Monk Mobs

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This female Hawaiian monk seal was not mauled by a shark but by a gang of males of her own species. A certain amount of aggression is normal for these seals during mating: for a male to mount a female in the water, he must bite her back to get a grip. But in recent years as many as two dozen frenzied males have been observed mobbing a female during assaults that can last several hours. Some females have been found with their backs slashed to the bone. Why do the seals engage in such a perverse mating strategy? For several years now, for reasons that puzzle biologists, there’s been an imbalance in the number of female and male monk seals on some Hawaiian Islands. Biologists are concerned because the species is already endangered--there are no more than 1,400 of the animals--but recently they’ve had reason to be optimistic. In 1994 biologists relocated 21 males from Laysan, an island on which males vastly outnumbered females, to the main Hawaiian Islands, stretching from Kauai to Hawaii. Tim Ragen of the National Marine Fisheries Service says that no seals died on Laysan from mobbing last year. Before the relocation program, Laysan lost an average of at least four animals annually. We didn’t expect that the removal of males would end the mobbing, he says. But we did hope that the mobbing would be significantly reduced, and that appears to be the case.

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