June 5, 2012
Australian Great White Shark Populations Separated By Genetics
Brett Smith for redOrbit.com
Despite inhabiting the same waters, two populations of Great White sharks living in the coastal waters of Australia are genetically distinct, according to a new study published in the journal Marine Ecology Progress Series.
The two groups of Great Whites, or white sharks, are separated by the Bass Strait, a stretch of water between the Australian mainland and Tasmania to the south. The research team, led by Dean Blower from the University of Queensland, used genetic tests from 97 shark tissue samples dating back to 1989 confirmed this geographical divide.
“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,” said Professor John Pandolfi, a Chief Investigator at the University of Queensland.
“Our tagging and tracking showed that white sharks travel thousands of kilometers,” said Barry Bruce, a lead study researcher from the Commonwealth Scientific and Industrial Research Organization (CSIRO).
“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,” Bruce said.
While previous work by other international research teams have identified separate genetic populations of white sharks across ocean basins, this is the first time such segregation has been found at the regional level.
The Bass Strait, which is named after George Bass who sailed around Tasmania in the late 18th century, measures 240 km across and averages about 50 meters deep. The shallow waters have been known to be notoriously rough and have taken down many sailing vessels. The strait has even been linked to a Bermuda Triangle-type mysticism at times.
White shark numbers declined in the 20th century as a result of fishing and other human activities, resulting in the species now being protected in South Africa, the United States, Australia, New Zealand, and several other countries under the Convention on International Trade in Endangered Species (CITES).
The effectiveness of the CITES treaty and other white shark related conservation programs has been difficult to assess because of a lack of information on abundance, genetic diversity, reproductive behavior and population. The creature´s elusiveness forces marine biologists and government officials to classify them as vulnerable because they appear uncommon when compared with the distribution of similar species.
“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,” said Jennifer Ovenden from Australia´s Department of Agriculture, Fisheries and Forestry.
Fishermen target many species of sharks for their jaws, teeth, and fins; as it is considered a game fish. The great white shark, however, is rarely an object of commercial fishing or shark finners because of the steep penalties associated with their possession.