Great whites aren鈥檛 all alike. Even though the sharks travel all over the Pacific Ocean to hunt, they tend to mate with others from the same area, forming genetically distinct groups.
That鈥檚 what local great whites revealed to of Stanford University in California and her colleagues. The team headed out into the Pacific to find the sharks, which they lured to the surface using a silhouette of a seal. They then used a pole to attach two different tags to the sharks and took a sneaky biopsy at the same time. See the .
GPS tags were used to track the long-distance movements of the creatures, allowing the team to follow their migration during the colder months from coastal areas to the deep ocean. The other tags gave off sonic 鈥減ings鈥� that were picked up by sensors moored in coastal areas, providing more precise location fixes than the satellite measurements, so that the team could tell if the sharks returned to the same areas.
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Caf茅 culture
Block noted that the sharks tended to follow a predictable, if mysterious route every year.
鈥淭hey go to an area we call 鈥榯he white shark caf茅鈥�,鈥� she says. Why this is such a cool place to hang out isn鈥檛 clear, however. The tags revealed that the females weave in and out of the males, and because there doesn鈥檛 seem to be much in the way of food at the caf茅 2000 kilometres off the California coast, Block thinks they may be mating.
The tags also confirmed the team鈥檚 theory that the sharks return to specific coastal sites in the summer. 鈥淭hese animals aren鈥檛 just wandering aimlessly through the sea,鈥� says Block. 鈥淭hey seem to maintain neighbourhoods.鈥�
Australian cousins
The tissue samples taken from the sharks showed that their mitochondrial DNA, which is inherited from the mother, was significantly different from that of great whites from the south-west Pacific. The group reckon that great white sharks originated around Australia and New Zealand and formed a separate group on the other side of the Pacific around 200,000 years ago, during the late Pleistocene epoch.
鈥淐alifornian sharks share a female ancestry with the Australian sharks from which they are derived,鈥� says geneticist , co-author of the study. 鈥淭he fact that males and females show similar, constrained migration patterns suggests that males are not breeding with other populations.鈥�
鈥淭his study adds important new layers of information to the story of sharks,鈥� says , manager of the Pelagic Fisheries Research Program at the University of Hawaii at Manoa. 鈥淭he genetic analysis confirms what previous satellite-tracking data suggested 鈥� that north-eastern Pacific sharks are separate from the south-western Pacific sharks near Australia and New Zealand.鈥�
The team hopes that knowing the migratory route of the great whites will aid conservation efforts, as the sharks are still threatened with extinction.
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