World-first hybrid shark found off Australia coast

The world's first hybrid shark — a cross between the common blacktip and the Australian blacktip — has been found off the east coast of Australia.

Researchers found 57 of the new sharks along 2000km of coastline between NSW to Queensland, and believe it is a sign the animals are adapting to climate change.

Scientists said on Tuesday that they had discovered the world's first hybrid sharks in Australian waters. The mating of the local Australian black-tip shark with its global counterpart, the common black-tip, was an unprecedented discovery with implications for the entire shark world, said lead researcher Jess Morgan.

"It's very surprising because no one's ever seen shark hybrids before, this is not a common occurrence by any stretch of the imagination," said Morgan, from the University of Queensland.

The find was made during cataloguing work off Australia's east coast when Morgan said genetic testing showed certain sharks to be one species when physically they looked to be another.

The Australian black-tip is slightly smaller than its common cousin and can only live in tropical waters, but its hybrid offspring have been found 2,000 kilometres down the coast, in cooler seas.

The common blacktip shark and the Australian blacktip shark are two species that are genetically distinct, and generally inhabit different temperature waters.

The larger common blacktip shark lives in the cooler sub-tropical waters off south-eastern Australia, but the hybrid species is able to survive in the tropical waters favoured by the Australian blacktip.

It means the Australian black-tip could be adapting to ensure its survival as sea temperatures change because of global warming.

"If it hybridises with the common species it can effectively shift its range further south into cooler waters, so the effect of this hybridising is a range expansion," Morgan said.

Climate change and human fishing are some of the potential triggers being investigated by the team, with further genetic mapping also planned to examine whether it was an ancient process just discovered or a more recent phenomenon.

If the hybrid was found to be stronger than its parent species -- a literal survival of the fittest -- Simpfendorfer said it may eventually outlast its so-called pure-bred predecessors.

The hybrids were extraorindarily abundant, accounting for up to 20 percent of black-tip populations in some areas, but Morgan said that didn't appear to be at the expense of their single-breed parents, adding to the mystery.

The study, published late last month in Conservation Genetics, could challenge traditional ideas of how sharks had and were continuing to evolve. This is telling us that in reality we probably don't fully understand the mechanisms that keep species of shark separate. 

Wild hybrids are usually hard to find, so detecting hybrids and their offspring is extraordinary.