Dall’s Porpoise

 

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Dall's Porpoise

Family: Phocoenidae
Genus: Phocoenoides
Species: P. dalli   (True, 1885)

These are extremely chunky animals with tiny heads and very small flukes and flippers. Dall’s porpoises sometimes cut through the water at tremendous speeds, sending up characteristic “rooster tails” behind and thin sheets of water over their backs. They are avid bow wave riders and sometimes will travel hundreds of yards for a free ride at the front of a ship. At other times, particularly when feeding, they are uninterested in ships.

Taxonomic Note: Animals with variable white flank coloration and which allegedly possess a greater number of teeth are referred to occasionally as Phocoenoides truii, or True’s porpoise. Recent observational research, however, confirms a vast and diverse mixture of color patterns within individual herds, seriously weakening the evidence for existence of a second species or subspecies.

Physical Description: These animals have very stocky bodies with small appendages. A slight forehead indentation is present at the blowhole, and a large hump is present on the dorsal ridge between the dorsal fin and the flukes.

Color: They are jet black, with white from the anus to the mid-belly and on the outer ridges of the flukes and dorsal fin, although many variations exist. Normally, the flanks are white from the head to the mid-peduncle region, but nearly all white and all black animals have also been observed.

Fins and Flukes: The dorsal fin is triangular, prominent, and pointed, located at the mid-back. The flippers are very small and rounded at the tips. The small flukes are nearly pointed at the tips with a slight median notch.

Length and Weight: They reach a length of 6.75 ft (2.1 m) and about 320 lb (145 kg).

Teeth: They possess 19 to 23 small, spade-shaped teeth in each side of the upper jaw, and about 20 to 24 in each side of the lower jaw.

Feeding: Their known diet consists of lantern fish, squid, and schooling fish.

Breathing and Diving: These animals are rapid swimmers, slicing through the water at high speeds, sending a jet of water above them. They are avid bow wave riders, and move quickly on the surface from right to left.

Mating and Breeding: Calves of 40 in (100 cm) are born in late July and early August. The gestation period lasts about a year.

Herding: They are found in groups numbering about a dozen.

Distribution: They are found in the immediate offshore waters of the North Pacific Ocean from Japan and southern California as far north as the Bering Sea.

Migration: They travel to the northern end of their range during the summer, southern end in the winter.



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