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Why are two-headed sharks becoming more common?

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For those who have a shark phobia, this could be their worst nightmare. Rising numbers of sharks with two heads are being born in the wild, according to scientists.
In the last few years, rising numbers shark species with these genetic abnormalities have been found by marine biologists and other researchers.
Shark expert professor Valentin Sans Coma, from the University of Malaga, has been looking at potential causes of what is believed to be a recent phenomenon.
Hehas been looking at the embryo of a two-headed catfish shark in a laboratory study, along with 800 other shark embryos.
So just why is this trend on the increase? Scientists can’t seem to agree. Professor Sans Coma said the most likely cause was a genetic disorder because he had ruled out any infection, chemicals or radiation.
But looking at the wider picture, scientists believe genetic mutations of sharks are down to a mixture of reasons, including viral infections, metabolic disorders and sea pollution.
After looking at a smalleye smooth-hound shark and a blue shark, both two-headed, marine biologist Nicholas Ehemann said he believed over fishing was at fault.
The professor said that because overfishing led to the shark gene pool being drastically reduced, it meant sharks which were closely related could be mating, leading to genetic disorders becoming more common now and in the future if fishing quotas aren’t put in place and adhered to.
The problem for scientists, who are trying to come up with a definitive reason why this could be happening, is that two-headed sharks do not tend to survive for very long.
Professor Ehemann said: “I would like to study these things, but it’s not like you throw out a net and you catch two-headed sharks every so often. It’s random.”
However, some scientists say that the picture is actually not becoming a more common one; it is simply that there are more pieces of research being carried out on the mutation.
The latest speculation comes after fisherman caught a bull shark which was pregnant with a two-headed baby shark in Florida in 2008. Meanwhile, another crew found a two-headed blue shark in the Indian Ocean.
Blue sharks are said to have produced the most recorded two-headed shark embryos as they carry up to 50 babies at a time.
It certainly, however, does not look like anyone will find a two-headed adult shark anytime soon.