Facts about dusky dolphin
- The Dusky dolphin (Lagenorhynchus obscurus) grows to about 2m in length and has virtually no beak.
- The dorsal fin is not hooked and is rather blunt.
- Colour is bluish-black on the back and tail and white on the underside of the body.
- Newborn: length c. 0.92 m
- Adult: female maximum length 1.93 m, male maximum length 2.11 m
Range
Dusky dolphin leaping out of the water
Main populations occur around South America, off south western Africa and in New Zealand waters. In New Zealand, dusky dolphins appear south of East Cape and are rare in more Northern waters. They have been recorded as far south as Campbell Island and east out to the Chatham Islands, with main populations occurring in Kaikoura and Admiralty Bay in the Marlborough Sounds. Large groups of several hundred to over 1000 dusky dolphins are present in Kaikoura all year round with individuals moving north to feed at Admiralty in winter months. Duskys are a highly coastal species and generally prefer waters less than 2000 m deep.
Population
Due to their coastal nature, populations of dusky dolphins around the world are discontinuous and reproductively isolated. Large-scale migrations are known to occur in New Zealand however, and inshore-offshore movements are made both diurnally and seasonally with dolphins moving further offshore in winter. Overall, group sizes range from two to over one-thousand. There are thought to be between 12,000 and 20,000 individuals in New Zealand (Markowitz, 2004). Dusky dolphins interact with a variety of other marine mammals including common dolphins, long-finned pilot whales, bottlenose dolphins, Hector's dolphins, killer whales, New Zealand fur seals, sperm whales, Southern right whales and humpback whales.
Diet and foraging
The diet of this species is dominated by anchovies, hake and several squid species. A variety of other small fish species is also eaten. In Kaikoura, dusky dolphins typically feed at night on prey associated with the deep scattering layer (Würsig et al., 1997). Individuals are known to adapt foraging methods to habitat and prey availability patterns, with the same dolphins, identified by natural markings, being found feeding cooperatively during the day in the Marlborough Sounds. Admiralty Bay is used regularly by 200-300 dolphins as a winter foraging habitat. Surface feeding activities occur in large groups accompanied by extensive aerial display and acrobatics, which are believed to help synchronize cooperative foraging. Cooperative foraging can also be seen between dusky dolphins and other marine mammals such as New Zealand fur seals (Markowitz, 2004).
Life history
Sexual maturity is reached at approximately 7-8 years. Calving in New Zealand occurs from November to mid-January. Gestation lasts for around 13 months and weaning occurs in less than 3 years. Dusky dolphins are estimated to live to ages of 30 years or more.
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