Bottle-nosed dolphins have long had the image of being intelligent guardians of the sea who speak their own language, enjoy the company of humans, and have even saved shipwrecked sailors from certain doom by leading them to land. Although these frolicking mammals may look friendly with their toothy smiles and playful gestures, marine biologists in mid-1999 were learning that dolphins also have a dark side that may include the capacity to kill.

In Shark Bay, on the coast of Western Australia, researchers from the University of Massachusetts in Dartmouth have observed gangs of male dolphins harassing and intimidating sexually receptive mature female dolphins. The researchers, led by biologist Richard Connor, documented several cases in which male dolphins, working in groups of twos and threes, “kidnapped” females from other dolphin groups. The females were then held captive for as long as one month.

This behavior appeared to be rooted in something other than simply aggressive tendencies. Based on observations of male dolphins in Shark Bay he had made since the 1980's, Connor believes that these gangs of male dolphins may be one of the few examples in nature in which the males of a species form stable long-term bonds with one another. In some cases, those bonds last more than 10 years.

Shark Bay, part of the Indian Ocean, has the largest sea grass beds in the world. The beds contain an abundance of fish and, because of the food source, a large number of dolphins. Because of this high concentration of dolphins, Connor and his team of researchers were able to study the formation and interactions of male social groups from boats in the clear waters.