SMALL CETACEANS (Less than 4 meters maximum length) 



This group includes most of the cetaceans known commonly as 

 dolphins or porpoises. Ten such species are reported from waters in or 

 near the CINMS, five as year-round residents or regular seasonal 



visitors and five as vagrants, extra-limital strays or rarely occurring 

 individuals difficult to detect or positively identify. 



Residents and Common Migrants 



Dall's Porpoise 



Phocaenoides dalli (True, 1885) 



In the northern North Pacific Ocean, the endemic Dall's porpoise is 

 the most frequently encountered and probably the most abundant 

 small cetacean. It is distributed widely in cool temperate to subpolar 

 waters, from the latitudes of central Ba|a Calitornia on the east and 

 southern Japan on the west, north to the central Bering Sea, including 

 the eastern Sea of Japan, the sea of Okhotsk, the Gulf of Alaska, and 

 inland marine waters of Washington, British Columbia and Alaska. 



The current population has been estimated at between 0.79 and 1.7; 

 million animals, although a more conservative minimum estimate of 

 580,000 recently reported apparently accounts for biases in data used to 

 derive the former estimates. The only direct commercial harvest of 

 Dall's porpoises is a traditional coastal harpoon fishery in Japan which 

 accounts lor annual harvests of about 6,000 animals. This species is, 

 however, killed incidentally in the Japanese high seas and land-based 

 drift net fisheries for salmon, which have operated in the North Pacific 

 and Bering Sea since 1952. Although most of this incidental mortality 

 occurs in the western half of the North Pacific, some occurs in the 

 United States' waters of the eastern North Pacific. Accurate data on 

 mortality are unavailable, but estimates indicate that between 2,2^0 and 

 20,000 porpoise have been entangled in gill nets and drowned annually 

 during years of greatest fishing effort. These figures are alarming to 

 conservationists and have been the catalyst tor international negotia- 

 tions between Japan and the United States about the future of the 

 fishery. There are few records of Dall's porpoise being caught in U.S. 

 fisheries. However, the increased use by U. S. fishermen of various 

 kinds of gill nets along the Pacific coast of North America has 

 increased the mortality of some coastal cetaceans, most likely including 

 Dall s porpoises. 



Although the Dall's porpoise is primarily a cold-water animal, its 

 range does extend south into Southern California, and even to Ballenas 

 Bay in Baja California. In winter we have frequently seen them at a 

 variety of locations in the Santa Barbara Channel, near Pt. Mugu, on 

 the south and west coasts of the northern Channel Islands and in open 

 water north of Santa Barbara and San Nicolas islands. We have also 

 seen them occasionally in the company of gray whales near Santa 

 Barbara Island, in the San Pedro Channel, near Santa Catalina Island 

 and near San Clemente Island. A few Dall's porpoises have stranded at 



San Miguel Island in recent years. Other researchers have reported 

 Dall's porpoises to be seasonally common in some years near San 

 Miguel, Santa Rosa, Santa Cruz and Anacapa Islands and near the 

 Santa Rosa-Cortes Ridge. Unpublished evidence available to us for 

 this review supports the hypothesis that while numbers of Dall's 

 porpoises in the SCB and adjacent waters of northwestern Baja 

 California increase in winter and spring there are small numbers of 

 year-round residents, at least around Santa Cruz and Santa Rosa islands. 

 They are frequently encountered on trips from Ventura and Santa 

 Barbara to Anacapa, Santa Cruz and Santa Rosa islands. 



Dall's porpoises usually occur in small groups (less than 20) 

 although on a few rare occasions groups of over 200 have been seen in 

 the SCB. Dall s porpoise occur only rarely in mixed species aggrega- 

 tions in the SCB, although further north they are often seen in the 

 company of harbor porpoises, particularly in the deep fjords along the 

 South coast of Alaska and in Prince William Sound. Although they 

 may often occur nearshore in northern waters, they generally occur 

 farther offshore [usually beyond the 100 fathom curve) in southern 

 areas, except where deep canyons approach the coast, such as in 

 Monterey Bay oft Pt. Mugu and near La Jolla, California. 



Little is known about the reproductive biology of the Dall's 

 porpoise. Two calving periods (winter, February through March; 

 summer, July through August) have been reported for portions of the 

 eastern North Pacific. Most recent evidence, however, suggests that in 

 the eastern Pacific parturition occurs throughout the year. Fetuses have 

 been taken from female Dall's porpoises in winter and spring months 

 near Monterey Bay, the Channel Islands and San Diego. Young, 

 nursing Dall's porpoises have been found stranded along the California 

 coast in February and July and newborn have been seen in Monterey 

 Bay in January and August and near Santa Catalina Island in February, 

 The calving interval is one year, on average, but the gestation and 

 lactation periods are not known. Some segregation ot the animals in 

 Monterey Bay seems to occur, with juveniles found close to shore and 

 larger adults well offshore. In offshore areas there may be further 

 segregation, with pregnant and lactating females being distributed 

 farther north than males and non-parous females. 



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