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Dall's Porpoise

The Dall's porpoise has a noticeable black and white colour pattern. The dorsal fin is black with a white base and the whole body looks quite massive. Dall's porpoises can swim very fast, up to 55km/h, and produce a characteristic splash which is called rooster tail. The splash makes it relatively easy to identify this species.

Males and females usually reach a length of about 1.80m (max. 2.29m) and a weight of 123kg (max. 160kg). Groups of these animals are usually small with 10 to 12 individuals but schools of up to 1000 porpoises have been observed. Since Dall's porpoises like to approach boats, especially fast boats (faster than 20km/h), to ride on the bow and stern wave, they are regularly seen. However these porpoises are not coastal animals but prefer deep water and may occur more than 1000km away from the shore. Dall's porpoises do not only ride on ship waves but also on the waves which develop in front of the snouts of fast swimming baleen whales. Although Dall's porpoises rarely breach (jump) they are often quite active and agile at the surface what makes it possible to see these animals even from bigger distances.

What do Dall's porpoises eat? Dall's porpoises are not specialized in a certain prey but feed on a high variety of fish (e.g. herring, anchovy, sardines, mackerel) and squid species and sometimes on crustacean. One animal feeds 12.7-13.6kg/day. To catch their food, these porpoises often dive up to 550m depth and even deeper. Also deep sea fishes like the lantern fish, are taken. Dall's porpoises feed mainly, but not only, during the night when deep sea fishes can be found much closer to the surface.

Female Dall's porpoises are sexually mature with an age of 3-7 years, males with 4-8 years. After 10-12 months of gestation an 85-100cm long calf is born. In most areas calving occurs in summer only and only every three years. Dall's porpoises usually live not longer than 20 years.

The Dall's porpoise occurs in temperate (cooler) waters of the north-Pacific, the Bering Sea, Okhotsk Sea and Sea of Japan with temperatures below 17°C. In Japanese waters many animals of this species are killed each year in the scope of the large-scale harpoon fishery. In 1988 39000 Dall's porpoises were hand-harpooned which corresponds to 1/3 of the western north-Pacific population. Another threat to this species is bycatch. In the late 1980's 6000 Dall's porpoises died annually in the high seas drift net fishery in the north-Pacific. Additionally the Japanese gillnet and salmon fisheries deplete the western stocks of these porpoises. During the two months salmon fishing season, 8000-10000 Dall's porpoises are taken incidentaly each year. The Japanese squid fishery is another factor which influence on the numbers of Dall's porpoises is unknown.

Since Dall's porpoises enjoy riding on bow waves of ships, censuses of this species failed in the past. If you like to count dolphins or porpoises, you drive by boat or fly by an air plane along a plotted line and count every animal you see. From those numbers calculations are carried out to estimate the size of a complete porpoise population by projecting from the data collected from boat/plane to a much bigger area which was never observed completely. Well, the problem is that all Dall's porpoises in the observed area came to the ships from which the census were carried out and areas further away were almost empty of them which the researchers did not know. Therefore population size was massively overestimated. In July 2001 the IWC passed a resolution calling for the stop of hunting of the Dall's porpoise until reliable population estimates are available, but Japan refused to comply.

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