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North Island Hector’s Dolphin

North Island Hector’s Dolphin

Vital Statistics

Hector DolphinsThe Hector’s dolphin (Cephalorhynchus hectori) is the smallest and rarest of the world’s 32 marine dolphin species. It is also the only dolphin endemic to New Zealand. It is much smaller than other New Zealand dolphins and is the only one with a rounded dorsal fin. Its snout is short and it has very distinct grey, white and black markings. Female adults grow to 1.6 metres long and weigh about 50 kilograms. Males are slightly smaller and lighter. Hector’s dolphins live for up to 20 years. Females reach sexual maturity at 7-9 years and produce only one calf every 2-4 years.

Hector’s dolphins make frequent short dives to catch a meal; the average dive lasts about 90 seconds. Like other dolphins, they use ‘echolocation’ to find their food. They send out high frequency ‘clicks that bounce off surrounding objects and fish, then echo back to the dolphins. The dolphin gets quite a detailed picture from the echo. For example, if a dolphin detects a fish it can work out what type of fish it is, how far away it is and how fast it is going.

Where are they found?

Distribution of North Island Hector’s Dolphin
The North Island Hector’s dolphin is found mainly between Kaipara Harbour and Mokau. Individual ‘pods’ are thought to keep within a 30 kilometre home range along particular pieces of shoreline and within 10 kilometres of the coast.

The pods, usually with 1-5 dolphins, are generally found inshore from spring through to autumn. It is thought that they spend more time further offshore during winter.

Recent studies suggest that there may now be fewer than 100 dolphins between the Kaipara Harbour and New Plymouth. There also appears to have been a reduction in range. Because of its very low numbers, slow breeding rate and the isolation of the individual populations, the North Island Hector’s dolphin is very vulnerable. It is now listed as a critically endangered species and, without help, it could soon become extinct.

South Island Hector’s dolphins are different from the ones found along the North Island’s West Coast. Although still thought of as one species, they are quite separate, isolated populations and scientists have found significant genetic differences between the two groups.


Why so few?

Set netting is one of the main threats to the dolphin. If a dolphin gets caught in a net, it cannot reach the surface to breathe and it drowns. Other factors, such as trawl fishing, boat strikes, climate change and pollution may also be contributing to the decline in dolphin numbers.

The fishing industry has come up with a proposal that aims to minimise its dolphin captures by commercial set-net fishers in the high risk area between Kaipara Harbour and New Plymouth. Key components of the plan include:

Closure of key areas
Gear restrictions
The use of ‘acoustic warning devices’ (pingers) by gillnet fishers targeting rig. Pingers emit a noise that is detected by dolphins, which stay away from the sound source
A research programme using log books that detail catch and effort information.
The Department of Conservation and the Ministry of Fisheries applaud this initiative and will continue to work with the fishing industry and environmental groups to monitor the status of the population and to investigate how best to achieve protection.

Research

There is still a lot that we need to know about the North Island Hector’s dolphin and its habits, if protection measures are to be applied effectively. How far do they range? How many are there? Where do they go in winter? Are the different groups closely related? What is the ratio of females to males? All these questions need answers and a number of different research methods could be used to help fill the information gaps. Techniques available include:

Aerial surveys to find out how many there are and their location.
Taking skin samples to genetically profile and identify individual dolphins.
Attaching satellite transmitters to the dolphins to give more detailed information about movements, range and dive behaviour.
You can help

If you are out in a boat and see dolphins (or other marine mammals):

Do not use set nets.
If approaching dolphins always do so from behind and keep parallel to them (see diagram). Don’t obstruct or cut through a pod.
Use a ‘no wake’ speed when within 300 m of dolphins.
No more than three boats should be within 300 m of a pod.
Do not swim with Hector’s dolphins.
Do not dump any non-degradable rubbish (e.g. plastics) at sea, especially near dolphins.
Do not throw out any food near dolphins.

Correct boating practice around Hector’s Dolphins
If you see a Hector’s dolphin (dead or alive) please record location, number of individuals, time and date of sighting and, if possible, photograph the dolphin. Pass this information on to your local Department of Conservation Area Office.