Two-headed Conjoined Porpoises Hauled Up from the Deep

By Tia Ghose, Senior Writer | June 15, 2017 07:39am ET 

Two-headed conjoined porpoises were recently hauled up by a fishing boat in the North Sea, not far off the coast of the Netherlands.

The bizarre-looking creatures were already dead, and the fishermen, who feared trouble from the authorities, took photos and then tossed the duo back overboard.

It's not clear exactly why the porpoises died, but the double-headed creatures likely could not swim, said Erwin Kompanje, a researcher at the Natural History Museum and the Erasmus MC University Medical Center in Rotterdam, the Netherlands, who recently wrote up the case in the June 7 issue of the journal Deinsea. Another cause may have been their fused hearts, which may not have worked adequately, Kompanje said. 

Conjoined twins

Conjoined twins are a rarity for humans, but they're also extremely rare for harbor porpoises (Phocoena phocoena), Kompanje said. That's because newborn dolphins and porpoises, which are mammals, need to immediately start swimming on their own or they drown, Kompanje said.

"Normal twins are extremely rare in cetaceans, as there is not enough room in the mother's body to have more than one fetus," Kompanje told Live Science. One case report pegged the incidence of twinning in cetaceans at less than 1 in 200.

Only one past case of a harbor porpoise bearing twins has ever been reported. Given the rarity of twinning, it stands to reason that conjoined twins are even more of an oddity, he added. In the past, only nine other cases of conjoined twins have been reported in whales or dolphins, and most of these were described in fetuses pulled from dead pregnant females, according to the study.

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Harbor Porpoises Can Thank Their Worst Enemy, the Killer Whale, for Their Success

June 12, 2013 — The harbor porpoise (Phocoena phocoena) is a whale species that is doing quite well in coastal and busy waters. They are found in large numbers throughout the Northern Hemisphere from Mauritania to Alaska, and now researchers from the University of Southern Denmark explain why these small toothed whales are doing so well: The harbor porpoise can thank their worst enemy, the killer whale, for their success.

Coastal areas are more challenging and potentially dangerous for a small whale. There is a risk of beaching and being caught in a fisherman's net, but there are also benefits. Fish are plentiful and easier to find in coastal waters than in the open sea.

Therefore, coastal waters are attractive for porpoises, and they are extremely skilled at navigating, locating prey and avoiding hazards near the coast. Like other toothed whales porpoises use echolocation for orientation and to detect prey. They emit a constant stream of sonar clicks, which, when these hit a rock, a fish or a ship nearby an echo is sent back to the porpoise. From the echo, the porpoise can distinguish the location of the object and often also can identify the object.

Porpoises can locate even small fish and small objects such as net floats and fine fishing nets. This ability sets them apart from many other toothed whales, which do not have such sophisticated echolocation abilities. The secret of this ability is that the porpoise uses very short clicks and these are higher in frequency than those of many other toothed whales, explains Lee Miller from the Institute of Biology, University of Southern Denmark (SDU).

Continued