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.
- 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
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).
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.
Threats to dusky dolphin
Killer whales and some shark species are the only confirmed predators of dusky dolphins. In order to avoid killer whales, dusky dolphins will move into shallower water and swim closer together.
Unknown numbers of dusky dolphins are caught in set nets in New Zealand waters each year. Current catches appear to have decreased from those of the 1970s and 1980s however. Possible future expansion of aquaculture at Admiralty Bay is likely to have an impact on dusky dolphin populations (Markowitz, 2004) through habitat fragmentation and competition for food resources.
You can help dusky dolphin
If you find a stranded dolphin:
Ring Department of Conservation immediately on:
0800 DOCHOTline (0800 362 468)
When boating in the vicinity of dolphins, common sense rules apply and regulations exist so as disturbance and danger are minimised. General rules are outlined below:
- Operate your boat slowly and quietly at "no wake" speed
- Manoeuvre your boat sensitively near dolphins. Do not obstruct their path, cut through a group or separate mothers from calves
- Avoid sudden noises that could startle the animals
- Cooperate with others so all may see the dolphins without putting them at risk
- Only swim with dolphins with authorised tourist operators and avoid wearing suntan lotion as chemicals in the water can irritate the animals' eyes
- Do not swim with dolphins when calves or juveniles are present
- Do not try to touch dolphins or feed them
Aircraft should also maintain a safe distance of at least 150 metres from dolphins and should not fly directly overhead.
Keep their environment clean by carefully disposing of any rubbish in appropriate receptacle, plastic waste can be particularly hazardous when discarded near waterways or beaches.
Sightings of dolphins can be reported to the 0800 DOC HOTline (0800 362 468). These are always of interest and help increase our knowledge of cetacean distribution and movements around New Zealand. Useful information includes:
- number of individuals
- estimated sizes
- what they appeared to be doing
- the direction in which they were headed.
If you see set nets being used within closed areas then contact the Ministry of Fisheries on 0800 4 POACHER (0800 4 76224).
If you accidentally catch or harm a dolphin you have a legal obligation to report it as soon as possible, but within 48 hours, to DOC or MFish.