Description - Dall’s Porpoise
Male Length: 2.3 m – Female Length: 2.0 m
Male Weight: 200 kg – Female Weight:: 130 kg
Life Span: 15 years
Dall’s Porpoise are generally very thick bodied and robust, with a
tiny head and little or no beak. The caudal peduncle is strongly keeled above and below, posterior to the anal region. Flippers are small and positioned far forward. The small dorsal fin is wide-based, triangular and positioned at mid body, the fin is canted forward and the trailing edge of their flukes is markedly convex. Adult males have a deeper caudal peduncle than females and a pronounced hump immediately behind the anus. There are 21 to 28 pairs of very small teeth in both the upper and lower jaws.
The porpoise is mostly black, with bright white patches on the flanks and belly. There are two consistent and well defined colour morphs. The dalli-type morph has a white flanks patch extending forward to approximately the level of the front of the dorsal fin: the true- type morph sees the patch extending farther forward reaching the flipper. Both the dorsal fin and the flukes become frosted with light grey, then white, as the animal ages; the white frosting on the dorsal fin usually has dark flecking.
Range and Habitat:
Dall’s porpoise are endemic to the cool temperate North Pacific and quite a prolific species in the inside passage of Vancouver Island.
Spending their time in small groups, from 2 to 12 individuals the Dalls’ porpoise loosely associates with other groups to form feeding aggregations involving dozens to hundreds of individuals. This porpoise is very fast, it is thought to be the fastest of all the small cetaceans. When surfacing, it typically creates “rooster tails” of spray that can almost obscure the animal itself. Dall’s porpoises are avid bow riders and often weave in and out of bow waves making jerky movements. This species is subject to predication by killer whales but its ability to swim at high speeds may minimise the threat of shark attack.Pacific White Sided Dolphin in the waters off Campbell River, Vancouver Island ~BC, Canada
The sexual dimorphism in body size and shape and the smallness of testes, suggest that the male Dall’s porpoises compete for exclusive access to females, as the males in such situations have a reduced need to produce large quantities of sperm. To achieve dominance they would need to be adept at fighting or alternatively, capable of intimidating one another with a visual display. Gestation lasts 10 – 11 months and birth takes place between early spring and early fall, mainly June to August. The lactation period lasts at least two months but for how much longer is uncertain. Females have been known to give birth annually during their prime.
Food and Foraging:
Diet consists mainly of schooling fish such as herring, pilchards, hake and squid. A high proportion of its diet consists of deep water, vertically migrating species. Their blubber is thin for a cold water species so they must maintain a relatively high metabolic rate and thus a high regular caloric intake.
Status and Conservation:
Abundant and wisely distributed, however the tendency to approach vessels makes it difficult to avoid overestimating their abundance. Many are killed each year in gill nets, trawls and other types of fishing gear. The greatest known threat is the porpoise hunt in Japan, where the annual harpoon kill of Dall’s porpoises increased in the 1980’s from thousands to several tens of thousands. Some years there have been reports of over 40,000 animals harpooned.