The results of a new study by a team of Australian researchers have revealed that there are two distinct populations of white shark (Carcharodon carcharias) occurring in the vicinity of the Bass Strait (the area of sea separating mainland Australia from Tasmania).
“The genetic makeup of white sharks west of Bass Strait was different from those on the eastern seaboard of Australia — despite the lack of any physical barrier between these regions,” explains Professor John Pandolfi from the ARC Centre of Excellence for Coral Reef Studies and the University of Queensland. “This shows that while the sharks can roam around Australia and across ocean basins, they repeatedly return to their home region to breed.”
Ocean Wanderers That Come Home
These findings also confirm data obtained by other scientists who have identified separate genetic populations in different ocean basins, though this is the first time that such localized divisions have been recognized.
“Our tagging and tracking showed that white sharks travel thousands of kilometers,” says CSIRO’s Barry Bruce, whose team has been carrying out both satellite and acoustic tracking of these feared predatory fish. “But sharks tagged and tracked off eastern Australia did not go west of Bass Strait, and sharks tagged off Western and South Australia rarely went east. When they did, they often returned so we started to wonder whether there was more than one breeding population.
“Now we know that while white sharks across Australia can mix, the intriguing thing is that they seem to return to either east or western regions to breed.”
Implications for Conservation
This discovery is not just of academic significance. It is likely to be critical to the conservation of this species in the future, providing vital insight into the population structures and reproductive behavior of white sharks.
“The finding may indicate that individual populations of white sharks are more susceptible than previously thought to threats including fishing or changes in the local marine environment,” Dr. Jennifer Ovenden from Australia’s Department of Agriculture, Fisheries and Forestry explains. “The key will be to develop regional rather than national management strategies, and to ensure populations are monitored in both regions.”
Reference: DC Blower, JM Pandolfi, BD Bruce, MdC Gomez-Cabrera, JR Ovenden. “Population genetics of Australian white sharks reveals fine-scale spatial structure, transoceanic dispersal events and low effective population sizes.” Marine Ecology Progress Series, 2012; 455: 229 DOI: 10.3354/meps09659