ANiMAL MUNDi: Who Needs a Dorsal Fin? by Corinna of TheFrogBag

by Corinna of TheFrogBag

Photos courtesy of Arkive.com

Who Needs a Dorsal Fin?

So what if dorsal fins are all the rage among seagoing critters? The Indo-Pacific finless porpoise (Neophocaena phocaenoides) certainly doesn’t care. This marine mammal is on the small side compared to most, measuring just seven feet long for a true giant of the species, and as its name suggests it doesn’t look much like other porpoises either. In fact, you might mistake it for a very slender manatee if you didn’t look too closely for its blowhole. 

Most aquatic animals use their dorsal fins as stabilizers against rolling when they make sharp turns. Picture a killer whale, hunting agile fish and sea lions. Finless porpoises are carnivores too, but they chase more sedate prey such as shrimp and prawns as well as various cephalopods. They haven’t opted for an entirely smooth back though. A ridge runs from their shoulder girdle to their tails, studded randomly with small tubercles that are rich with nerve endings. These rough bumps were once thought to act as a slip-resistant way for mother porpoises to carry their young. In fact that is probably of secondary importance to their use as sensory organs. 

Unlike some of their more gregarious cetacean cousins, little is known about how and when finless porpoises breed. Their shy demeanor makes them difficult to study, as does their tendency to seldom form groups of more than two individuals at a time. When they are spotted it’s usually in the waters off China, Japan, and Indonesia, in shallow bays and estuaries. There’s even a population that lives in the fresh water Yangtze River in China. 

Given the fact that they reside so close to humans it’s no surprise that habitat loss is the biggest threat facing these charming creatures. Shrimp farms, near-shore pollution, and deforestation of mangrove swamps are contributing factors to the steep decline of their populations. Fortunately, conservation organizations like the World Wildlife Fund are stepping in to help. With an intellect that is said to rival that of the gorilla, finless porpoises will hopefully continue to ply the waters of Asia for years to come.