The year 2016 has just ended, but that doesn’t mean that the bad news it brought is over and that everyone gets a clean slate. The news of the increasingly common phenomena of two-headed sharks started circulating at the close of 2016 and is haunting everyone who has ever claimed they would never swim in the ocean because they’re afraid of sharks.
The good news is that, like many other animals born with mutations, the two-headed varieties of sharks don’t live for very long so you’re not likely to run into any adult ones in the wild. However, what’s alarming is that the number of sharks found with this mutation has been growing in the last decade.
In 2008, a fisherman discovered a two-headed blue shark embryo in the Indian Ocean and just a few years ago a fisherman off the coast of Florida found a similar embryo in a bull shark’s uterus. Because of the increasing discoveries of this nature, a study was launched in 2011 that studied “embryonic bicephaly” in blue sharks. Researchers focused on blue sharks because they’ve produced the most-recorded number of two-headed embryos because they carry up to 100 babies at a time and give birth to live young.
The most recent case popped up in 2016 when a group of researchers raising sharks in a laboratory noticed the two-headed embryo in a shark egg. What makes this case special is that it was the egg of a sawtail catfish and it was the first recorded case of bicephaly occurring in a shark that lays eggs.
So why the sudden increase in these abnormal cases? Researchers believe that malformations found in wild sharks may be caused by a variety of factors, one being overfishing. When humans overfish, the gene pool diminishes and causes inbreeding. Humans know that birth defects occur when inbreeding happens, which is what happens to the sharks who engage in the same practice.
Other factors could be pollution, metabolic disorders, viral infections, or just plain excessive documentation. Galván-Magaña, author of the 2011 bicephaly study, said that there are more scientific journals that are more widely available where such accounts can be documented, making it seem like the number of cases is growing.
Whatever the case may be, it’s likely no cause for alarm since the sharks don’t grow into adulthood, but if it’s humans that are behind this shift in defects then it’s best to attempt to lower your trash pollution to prevent these types of nightmarish consequences.