Great white sharks are almost mythical in their allure. But in a paper published in today's issue of Nature, scientists elucidate one more aspect of the mysterious lifestyle of the big fish: the males tend to roam between the earth's oceans to a much greater extent than previously thought, while females tend to stay closer to home.

The researchers analyzed and compared DNA from 95 sharks in two oceanic locations: waters near Australia and New Zealand and in the South African coastal zone. Maternally-inherited mitochondrial DNA from the two populations were significantly different. Genes passed on by both sexes, on the other hand, were similar, suggesting greater dispersal of the males than earlier tagging data had indicated.

"The results were somewhat of a surprise," co-author Andrew Martin of the University of Colorado, Boulder, says. "Many of us thought both male and female sharks were moving all over the place, but the mitochondrial DNA results indicates there was a significant divergenceprobably two to three million years agobetween the sharks from Australia and New Zealand and those from South Africa."

The findings suggest that sharks may behave more like marine mammals than fish in terms of their mating behavior. The authors caution that the numbers of great white sharks could decline rapidly if people hunt populations that have non-roving females and low numbers of males migrating from surrounding stocks. "Management practices need to take into account the importance of breeding grounds and the connections of widely separated populations," Martin says. "A globally integrated plan of regional management would be the ideal situation."