Is it a dolphin or is it a porpoise? That was the question for this amazing sighting by a top coarse angler on the tidal Thames near the river's upper tidal limit in South West London.

The full report on this remarkable River Thames dolphin – or porpoise – sighting is in Angler’s Mail magazine, out now!

The difference between a dolphin and porpoise

Dolphins and porpoises are often mistaken for each other, and the video above may not be conclusive proof of which species was spotted on the Thames by an Angler’s Mail reader. So what’s the difference?

According to the National Ocean Service: “It essentially comes down to their faces (who can forget Flipper’s famous “grin”?), their fins, and their figures.

Dolphins leaping - one of nature's finest sights.

Dolphins leaping – one of nature’s finest sights.

“Dolphins tend to have prominent, elongated “beaks” and cone-shaped teeth, while porpoises have smaller mouths and spade-shaped teeth. The dolphin’s hooked or curved dorsal fin (the one in the middle of the animal’s back) also differs from the porpoise’s triangular dorsal fin. Generally speaking, dolphin bodies are leaner, and porpoises’ are portly.

“Dolphins are also more talkative than porpoises. Dolphins make whistling sounds through their blowholes to communicate with one another underwater. Scientists are pretty sure that porpoises do not do this, and some think this may be due to structural differences in the porpoise’s blowhole.

are a group of fully aquatic marine mammals, that are sometimes referred to as mereswine.

Porpoises are a group of fully aquatic marine mammals, that are sometimes referred to as mereswine.

“Dolphins and porpoises have many similarities, one of which is their extreme intelligence. Both have large, complex brains and a structure in their foreheads, called the melon, with which they generate sonar (sound waves) to navigate their underwater world.

“It is likely that more (or fewer) differences between dolphins and porpoises will be revealed as researchers continue to investigate these intriguing sentinels of the sea.”