Scientists have discovered the first hybrid shark off the coast of Australia, finding 57 hybrids between the common blacktip shark and the Australian blacktip shark along 2,000 km of coastline. This discovery suggests shark species may respond to changing ocean conditions by interbreeding. The hybrid sharks have been found swimming over 1,000 miles south of the typical range of Australian blacktips, indicating the hybrids may have an evolutionary advantage in a changing climate by allowing the species to better adapt to different conditions. Researchers first realized something unusual was occurring when sharks' genetic analysis showed they were one species but had physical characteristics of another.

1. Australia: Scientists discover rst hybrid shark
Juliet Eilperin, Washington Post
Thursday, January 5, 2012
Scientists have identi ed the rst-ever hybrid shark o the coast of Australia, a discovery that suggests some shark species may
respond to changing ocean conditions by interbreeding with one another.
A team of 10 Australian researchers identi ed multiple generations of sharks that arose from mating between the common black-
tip shark (Carcharhinus limbatus) and the Australian blacktip (Carcharhinus tilstoni), which is smaller and lives in warmer waters
than its global counterpart.
"To nd a wild hybrid animal is unusual," the scientists wrote in the journal Conservation Genetics. "To nd 57 hybrids along 2,000
km (1,240 miles) of coastline is unprecedented."
James Cook University Professor Colin Simpfendorfer, one of the paper's co-authors, emphasized in an e-mail that he and his col-
leagues "don't know what is causing these species to be mating together." They are investigating factors including the two spe-
cies' close relationship, shing pressure and climate change.
Australian blacktips con ne themselves to tropical waters, which end around Brisbane, while the hybrid sharks swam more than
1,000 miles south to cooler areas around Sydney. Simpfendorfer said this may suggest the hybrid species has an evolutionary ad-
vantage as the climate changes.
As a result, he wrote, "We are now seeing individuals carrying the more tropical species genes in more southerly areas. In a chang-
ing climate, this hybridization may therefore allow these species to better adapt to di erent conditions."
The researchers - who had been working on a government-funded study of the structure of shark populations along Australia's
northeast coast - rst realized something unusual was going on when they found sh whose genetic analysis showed they were
one kind of blacktip but their physical characteristics, particularly the number of vertebrae they had, were those of another. Shark
scientists often use vertebrae counts to distinguish among species.
The team also found that several sharks that genetically identi ed as Australian blacktips were longer than the maximum length
typically found for the species. Australian blacktips reach 5.2 feet; common blacktips in that part of the world reach 6.6 feet.