Warmer sea may 'cause' hybrid shark
SHARKS off the east coast of Australia could have been interbreeding and creating hybrid species for many years, a shark expert from Southern Cross University says.
Dr Danny Bucher, a senior lecturer in marine biology and fisheries at SCU's School of Environmental Science and Management, said the recent discovery of hybrids of the Australian black tip shark and the common black tip shark was "an interesting find".
Scientists found 57 hybrid sharks between northern NSW and far north Queensland.
Although the two species are similar, they grow to different sizes and are genetically distinct.
Dr Bucher said hybrids often occurred between closely related species.
However he also said that it had not been known in sharks, until now.
"Neither of the parent species is a danger to humans, so the hybrids are not a threat," he said.
"They may be more hardy than their parent species, but so-called 'hybrid vigour' often comes at a cost, for example mules are stronger and hardier than horses or donkeys but are infertile."
Dr Bucher said he had seen interbreeding in other fish and marine life, but never in sharks.
"This (interbreeding) is something that isn't really that common on the east coast in general," he said.
"But it is quite possible that it may have been going on for a long time; we just haven't noticed it yet.
"It is unusual, even thought the two species are very similar.
"Hybridisation can occur when closely-related species that have evolved in isolation come back into contact.
"It is possible that the two species had adapted to different climate conditions are coming into contact more often as waters warm near their natural boundaries.
"Maybe it's related to climate change; it is difficult to say.
"After all no one had done the genetics before this and it would have been difficult to identify hybrids from appearance alone."
Scientists from the University of Queensland, James Cook University's Fishing and Fisheries Research Centre, the Queensland Department of Employment, Economic Development and Innovation and the NSW Department of Primary Industries have been involved in the discovery.
They used both genetic testing and body measurements to identify the hybrid sharks in five locations, spanning 2000km from northern NSW to far northern Queensland.
Dr Jennifer Ovenden from the research team said this was the first discovery of sharks hybridising and it flagged a warning that other closely-related shark and ray species around the world may be doing the same thing.
"Wild hybrids are usually hard to find, so detecting hybrids and their offspring is extraordinary," she said.
"To find 57 hybrids along 2000km of coastline is unprecedented."
She also said hybridisation could enable the sharks to adapt to environmental change.
The scientists are now investigating the full extent of the hybrid zone and are attempting to measure hybrid fitness.