Dall's Porpoise
The Dall's Porpoise is a species of porpoise found on the North Pacific. It came to worldwide attention in the 1970s when it was disclosed for the first time to the public that salmon fishing trawls were killing thousands of Dall's porpoises and other cetaceans each year by accidentally capturing them in their nets. The Dall's porpoise is the only member of the Phocoenoides genus. It was named after American naturalist W.H. Dall.
Physical Description[]
The unique body shape of the Dall's porpoise makes it easily distinguishable from other cetacean species. The animal has a very thick body and a small head. The colouration is rather like that of a killer whale; the main body of the porpoise is very dark grey to black creeper, with very demarcated white patches on the flank and belly. The dorsal fin is set just back from the middle of the back and sits up erect. The upper part of the dorsal fin has a white to light grey "frosting".
The fluke has a similar frosting. The adult fluke curves back towards the body of the animal, which is another distinguishing feature. It is larger than other porpoises, growing up to 2.3 m (7.5 ft) in length and weighing between 130 and 220 kg (290 and 490 lb). There is also sexual dimorphism in the species, with males being larger, having a deeper caudal peduncle and a pronounced hump behind the anus. Young Dall's have a greyish tint and dark-colored flukes.
Habitat[]
The Dall’s porpoise prefers cold waters more than 180 meters (590 ft) deep . It is found over the continental shelf adjacent to the slopes and oceanic waters. While it mostly lives in offshore waters, it does occur in deep coastal waters on off North America. There, it typically stays close to deep-water canyons.
Food[]
Dall’s porpoises primarily eat small fishes (of numerous species) and cephalopods. Schooling fish, such as herrings, anchovies, pilchards, mackerels, hake and sauries are favored prey, as well as mesopelagic fish such as myctophids and deep sea smelts. They may also consume krill, but these are probably not important in their diet.
Behavior[]
Dall's porpoises are highly active creatures. They will often zigzag around at great speed on or just below the water surface, creating a spray called a "rooster tail". They may appear and disappear quite suddenly. The fastest of all small cetaceans, Dall's porpoises can swim at up to 55 km/h, almost as fast as the killer whale. The porpoises will approach boats and will bow- and stern-ride, but may lose interest, unless the boat is travelling quickly. They will also "snout ride" on waves made by the heads of large whales. They may also do more calm behaviors, such as subdued rolls at the surface. They rarely leap from the water. Dall’s porpoise are also deep divers. They have been recorded to dive to 94 m.