Hector's Dolphin
Hector's dolphins Cephalorhynchus hectori hectori are endemic to New Zealand, meaning they are only found in New Zealand's waters.
In 2003 scientists completed genetic studies and taxonomic studies and determined that the North Island population was genetically and morphologically different and should be classified as a different subspecies. What had once been a single dolphin species then became two: the North Island Hector's dolphin subspecies was re-named Maui's dolphin, Cephalorhynchus hectori maui and the South Island species remained the Hector's dolphin.
Maui's and Hector's dolphins are the smallest and rarest of the world's 32 marine dolphins. Maui's dolphin and Hector's dolphin are visually very similar and are much smaller than other dolphins found in New Zealand waters. They are the only dolphins with a rounded dorsal fin and have very distinct grey, white and black markings. Compared to other dolphins the snout is short. Female adults grow to 1.6 metres long and weigh about 50 kilograms. Males are slightly smaller and lighter.
It is believed that the dolphins live for around 20 years and that females reach sexual maturity at seven to nine years, producing only one calf every two to four years. Maui's and Hector's dolphins diet includes small fish such as mullet and cod as well as squid.
Distribution – Maui’s Dolphin
Maui's dolphins are found between Kaipara Harbour and North of New Plymouth. Individual ‘pods' (usually with one to five dolphins) keep within a 30 kilometre home range along particular pieces of shoreline and are generally sighted within one nautical mile (1.8km) of the coast. This range includes harbour entrances and river mouths. There have never been any verified sightings of Maui's dolphins within harbours.
The pods are generally found inshore from spring through to autumn and are believed to spend more time further offshore during winter, although this varies around the coast and could be influenced by availability of food sources, water depths, predators and other conditions.
Distribution – Hector’s Dolphin
Three subpopulations of Hector's dolphin have been identified in the South Island that are genetically distinct and are geographically separated. These are found on the east coast of the South Island, the west coast of the South Island and the south coast of the South Island. Occasional inter-breeding does occur between adjacent populations.Threats to Population Numbers
Maui's dolphins are listed as a critically endangered species. One of the classification criteria is the number of mature adults in the population. Population estimates from 2004 of Maui's dolphin suggest that there may be between 48 and 252, with a point estimate of 111, Maui's dolphin numbers are threatened by mortality from natural causes, (e.g. predation by sharks) and by the direct and indirect activities of humans. Dolphins can be caught in nets set by commercial and recreational fishers, and dolphins can be killed or injured in collisions with boats. Because the dolphins live close to shore there is concern that pollution could be affecting their mortality rate. The presence of the Brucellosis bacteria, identified as the cause of death in the most recently autopsied bodies is of concern. Increased sediment run off from land use practices may also pose a threat by adversely affecting the food sources of the dolphin.What the Industry Can Do To Mitigate Dolphin Interactions
In the 25 years since it was discovered that the slow reproductive rate of Hector's and Maui's dolphins meant that recreational and commercial setnet by-catch was of concern, a number of measures have been taken to reduce the chance of entanglements occurring.
Education has been crucial along with the willingness of fishermen to change their practices to protect dolphins. The good news is that the number of known commercially caught Hector's dolphins has reduced dramatically and today it is a relatively rare event. Measures to help dolphins include:
- Setnet Codes of Best Practice adopted
- Voluntary Closed Areas introduced in the Canterbury region
- Use of Acoustic Alarms on nets (‘pingers') promoted
- Funding of over 10 years of observer programmes at a cost of $957,000
- Keeping nets well maintained, set tight and retrieved as early as possible
- Areas where water is shallow, murky or discoloured are avoided
- Set nets are not be deployed or hauled when dolphins are active around the vessel
- Fish finders are left on during setting and hauling to alert dolphins of the presence of nets.
- Addtionally, the government closed set netting out to 4 nautical miles in 2003 after industry proposed mitigation measures. This has been successful with zero maui dolphin deaths attributed to fishing since this time. In addition Ministry of Fisheries observers have spent 136 days on inshore trawlers on the West Coast of the North Island to see if any interactions with Maui dolphins occur. None have.