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Dallís Porpoise Phocoenoides dalli

Dall's Porpoise facts:

Length: 1.8 meters

Weight: 123 kg

Food: squid and school fish

Social Status: Commonly found in groups of 10 - 20

Sexually mature at about 2 years

Breeds annually to 1 calf

Gestation: 10-11 months

Newborn: 95-100 cm long

Adult life expectancy: about 10 years, oldest 22 years.

IUCN Red List Status: Lower Risk

 

Porpoises have flattened spade-shaped teeth and their forehead is convex at the tip of the upper jaw. Dolphins have sharp conical teeth and their forehead is concave at the upper jaw.

The Dallís porpoise is a widespread and numerous species in the North Pacific, and yet much is to be learned about the species. It lives along the coast and in the open ocean from California to Japan. It prefers deep canyons in coastal areas and where water is cold. It is likely that these places have the greatest prey abundance.

Adult porpoises are mostly black in colour with white flanks and white tipped fins. Young porpoises are grey with white flanks. Reeves et al.ís (2002) book has excellent illustrations of age classes. Two types of Dallís porpoise occur - the truei type is found in the western Pacific off Japan and the dalli type along the Pacific Coast of North America. The western Pacific form has a white lateral patch extending to the pectoral fins whereas the white lateral line on the dalli type reaches only to the mid line of the dorsal fin.

Estimating the number of Dallís porpoises is difficult because of their wide ocean going range. Estimates range from several hundred thousand to 1 million animals but there is not much certainty in these estimates. Dallís porpoise is often attracted to moving boats to ride the bow wave and schools of 2 to 12 animals are most common.

Calves are born in June and July, and mating occurs soon after the calves are born. Calves stay with their mothers until the next calf is born. They then gather with other immature porpoises and adult males in the southern part of the range. Dallís porpoises eat deepwater fish and squid probably at night, and schooling fish such as herring, anchovy, hake and juvenile rockfish during the day. Orcas and sharks prey on porpoises. There are excellent photographs of orcas hunting porpoises on page 19 in Ford et al. (2000) and page 473 in Reeves et al. (2002). Baird et al. (1998) reported the first hybridization for the species. They found a 60-cm female fetus in a dead Dall's porpoise in southern British Columbia that was fathered by a harbour porpoise (Phocoena phocoena).

 

References

Baird, R. W. Pamela M. Willis, Tamara J. Guenther, Paul J. Wilson and Bradley N. White. 1998.  An intergeneric hybrid in the family phocoenidae. Canadian Journal of Zoology 76:198-204.

Ford, J. K. B., G. M. Ellis and K. C. Balcomb. 2000. Killer whales. Second ed. University of British Columbia Press, Vancouver.

Murayama, T. and others. 1992. Histological characteristics and distribution of ganaglion cells in the retinae of the Dallís porpoise and minke whale. Pp. 137-145 in Marine Mammal Sensor Systems (JA Thomas et al. eds.). Plenum, New York.

Reeves, R. R., B. Stewart, P. Clapham and J. Powell. 2002. Guide to marine mammals of the world. Alfred A. Knopf, New York.

Walker, W. A. 1996. Summer feeding habits of Dallís porpoise Phcoenoides dalli, in the southern Sea of Okhotsk. Marien Mammal Science 12:167-181.

Wilson, D. E. and S. Ruff (eds). 1999. The Smithsonian book of mammals. Smithsonian Institution, Washington DC.

 

 (written March 2005)

 

 

 
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