Footage of an extremely rare whale with two dorsal fins is puzzling

An extremely rare double dorsal fin humpback whale has been filmed swimming in Australia.

Video posted by John Natoli to the Cetal Fauna Facebook group shows the whale breaching the surface of the water off Brunswick Heads, Byron Bay. Its two dorsal fins are clearly visible.

In a caption for the video, Natoli said the phenomenon was spotted by Blue Bay Whale Watching skipper Mark Wraight.

Around 99.9 percent of the whales sighted off the coast of Byron Bay are humpback whales. Whale watching season in the area typically ends in late October when the humpback whales migrate.

The phenomenon is not easy to explain.

Vadim Pavlov, a research scientist at Hopkins Marine Station at Stanford University, recounts news week that he has never seen it.

“Usually, the different types of unusual dorsal fin shape are associated with trauma from a collision with a boat. You can find a number of photos of it online. What I can see on the video you sent me doesn’t appear to be an old wound, but rather a doubling of the dorsal fin,” Pavlov said.

“It appears as an atavism previously described in whales and dolphins. But this case has one clear difference: all known cases are the rudimentary fin-shaped hind appendages. The uniqueness of this case is that the dorsal fin (as well as tailworms) is the de novo structure of cetaceans, unrelated to the appendages.

“So the appearance of a second dorsal fin is not linked to the evolution of cetaceans and their terrestrial ancestors. It could be linked to abnormal prenatal development.”

Amanda L. Bradford, a research ecologist with the NOAA Cetacean Research Program, narrated news week that it is difficult to know what caused this “other than being a physical abnormality caused by a genetic mutation”.

Bradford said environmental factors could also play a role.

Although rare, this phenomenon appears to have been observed in other whales.

Other Facebook users commented on the post, believing that this was actually a well-known whale in the area known as “Spiky”.

A user posted a picture of a very similar looking whale swimming in Tonga in 2017. Responding to the comment, Natoli said it definitely appears to be the same whale.

Another user posted a picture of Spiky as a calf in 2001. It’s not clear how many times Spiky has been spotted over the past 21 years.

The Facebook user said there had even been sightings of triple dorsal finned whales.

A humpback whale breaches the water
A stock photo shows a humpback whale breaching the water. A whale with two dorsal fins has been spotted in Australia.
Mark Malleson Footage of an extremely rare whale with two dorsal fins is puzzling

Rick Schindler

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