Two-headed sharks, a rare phenomenon, have been appearing globally, leaving scientists intrigued about the underlying causes. These unusual creatures have been found in various parts of the world.
Off the coast of Florida, fishermen once discovered a bull shark with a two-headed fetus in its uterus. In 2008, another fisherman found a two-headed blue shark embryo in the Indian Ocean. Additionally, a 2011 study reported conjoined twins found in blue sharks caught in the Gulf of California and northwestern Mexico. Blue sharks are particularly notable for producing the most recorded two-headed embryos due to their ability to carry many offspring—up to 50 at a time.
Recently, Spanish researchers identified a two-headed embryo of an Atlantic sawtail catshark, marking the first instance of such a specimen in an oviparous shark species, which lays eggs. Researchers examined the unusual embryo while studying sharks in a laboratory setting, but it remains uncertain whether the deformed animal would have survived. Typically, offspring with such deformities do not live long enough to be discovered.
The exact causes of these two-headed sharks remain uncertain due to their rarity. Researchers suggest that genetic disorders could be a plausible explanation, especially since the embryos were grown in a controlled lab environment with no known exposure to infections, chemicals, or radiation.
In the wild, malformed sharks could be the result of various factors, including viral infections, metabolic disorders, pollution, or a dwindling gene pool due to overfishing, leading to inbreeding and genetic abnormalities.
While two-headed blue sharks are relatively more common due to the large number of eggs produced by females, the increase in reported cases may also be attributed to greater scientific awareness and publishing opportunities. Researchers have also come across other unusual shark deformities, such as a “cyclops” shark with a single functioning eye at the front of its head, observed off the coast of Mexico in 2011.
The study of shark deformities remains challenging due to the rarity of such specimens. Researchers express interest in further investigating these occurrences but acknowledge that they are unpredictable and infrequent events in the natural world.