Incredibly rare two-headed porpoise found in the North Sea

Speculation has been rife after Dutch fishermen caught a two-headed newborn harbour porpoise in the North Sea.

The fishermen were afraid of keeping their rare catch as they didn't know if it was legal to keep the marine creature. Only one case of twin porpoises has been previously documented.

Fishermen off the coast of the Netherlands accidentally made history when they discovered the world's first example of a conjoined twin harbor porpoises. The discovery was documented by Erwin Kompanje of the Natural History Museum Rotterdam and coauthors in the online journal DEINSEA last week.

Porpoises generally give birth to a single offspring every year or two, according to National Geographic.

The fishermen took photos of the porpoises and then returned them to the sea, believing that it would be illegal to bring the animal to shore. In fact, this recent discovery is only the 10th such case of conjoined twins to be found among cetaceans, which means that researchers have little data to go on regarding such phenomenon.

"Normal twins are extremely rare in cetaceans", adds Kompanje.

Though being unable to physically inspect the porpoise, the unhappy researchers believe that they could possibly garner facts from the fishermen's pictures of the freaky creature. Also, the creature still contained an umbilical opening and the tail had not yet stiffened, which is important for porpoises to swim - these factors signified that the porpoise passed away shortly after its birth. The dorsal fins were not yet erect, and the tops of its heads still have hairs on them. They've determined that the porpoise nearly certainly wasn't capable of actually swimming, due to an underdeveloped tail section which would have immobilized it.

Upon their return to port, they alerted local authorities and research groups, who were very intrigued by the find, but were disappointed at the lack of a physical specimen.

An accidental catch in trawling nets poses the greatest danger to porpoises, the International Union for the Conservation of Nature says.

Conjoined twins likely form in cetaceans in the same way they do in humans; either two separate embryos fuse after having separated, or a single embryo fails to completely split. The European Union is taking measures to reduce the threat. However, Kompanje noted that what caused the conjoined twins still remains a mystery.

  • Carolyn Briggs