Maui's dolphin

This information has been reviewed.

The Maui's dolphin used to be called the North Island Hector's dolphin until 2002, when based on genetic and skeletal differences the subspecies Maui's dolphin was described by Dr Alan Baker. The name of the subspecies is based on the Maori indigenous name for the North Island, which is Te Ika a Maui.

This animal is severely threatened by fisheries bycatch, and recent sensitivity analysis has predicted extinction within the next few decades unless all net fishing (including gillnet and trawl fishing) is banned within its range.

A rare and small cetacean, this dolphin is identified by a solidly built body with a gently sloping snout and a unique rounded (mickey mouse ear shaped) dorsal fin.

Most of its time is spent feeding, while it also observed to play, for example with seaweed, chase other dolphins, blow bubbles, fight and jump.

Size

Adults measure between 1.2-1.4 m and weighs up to 50 kg.

Colour

The sides and back of this dolphin are light grey, with white "flames" reaching up along the sides of its body. The underside is whitish, while the face, flippers, the dorsal fin and tail are all black. There is a crescent-shaped black mark between eyes and blowhole.

Ecology and Habitat

Slow breeding rate = high survival vulnerability

The subspecies is found in inshore waters, including river mouths, estuaries, harbours and shallow bays, commonly within about 5 nautical miles of the shore.

Social Structure

Mothers and calves often travel in small nursery groups for protection.

This dolphin tends to occur in groups of up to five individuals, which may aggregate temporarily. Young are reported to play with seaweed, blow bubbles and are involved with other 'games' which are considered to be important social behaviours. Hector's dolphin emits sounds that are thought to be used for communication, notably the complex clicks produced in large groups.

Life Cycle

Calves live on their mother's milk for up to a year, although they learn to eat fish and squid after about 6 months. Females mature sexually at 7-9 years old.

Breeding

Like other small dolphins, Maui's dolphins have a low reproductive rate - they breed just fast enough to replace the number of dolphins that die naturally. This slow birth rate means that Maui's dolphins are struggling to recover from human induced deaths.

Maui's dolphins do not pair for life but mate frequently. Females give birth to a single calf every 2 to 4 years, which is born with dorsal fins partly folded over and with fold marks along the bodies. The calf is large (50 - 60 cm) in proportion to its mother (only 1.2-1.4 m).

One female might have four calves in her 20 year life span.

Diet

Maui's dolphins spend most of their time making short dives (90 seconds or so) to find fish on the sea floor. They also feed on fish and squid in mid water and sometimes close to the surface.

Population and Distribution

Now found only in isolated pockets

Previous population and distribution

The first survey of Maui's dolphins in 1985 estimated the total population at 134. For example, Maui's dolphins were seen regularly in the Taranaki area in the 1970s. Today they are no longer present there.

Current population and distribution

Maui's dolphins are found in isolated pockets along the North West coast of the North Island, between Dargaville and New Plymouth. They live in small pods of 1 to 5 dolphins within 5 nautical miles of the coast.

During summer (October to March) they seem to venture closer to shore and are mostly seen within 1 nautical mile of the coast. It is thought that individuals remain within the same 60 km stretch of coast all their lives. A January 2004 survey confirmed the small population size of around 100 dolphins.

What are the main threats to Maui's dolphins

Prey to fine nylon nets

A slow breeding rate and small population size have made of Maui's dolphin a very endangered subspecies. In fact, just more than one human-induced death every seven years seriously threatens the chances of population recovery.

However, over since March 2001, seven dead Maui's dolphins have been found. Five of these deaths were due to fishing, one was impossible to determine and one was because of natural causes. This dolphin is vulnerable to set net (gill net) and trawl fishing, marine pollution and debris, boat strikes and genetic bottleneck.

Set net (gill net) and trawl fishing

The most significant threat to Maui's dolphins is from set net fishing. Dolphins do not seem able to detect the fine nylon nets with echolocation and swim into them.

They cannot swim backwards so are unable to free themselves from the net. Since they cannot reach the surface to breathe, they drown within a couple of minutes. A set net ban is in place in part of the dolphin's range. The ban at this stage does not fully include harbours yet, even though dolphins have been sighted there.

In the South Island, Hector's dolphins have drowned in coastal trawl nets. It appears there is a risk to the Maui's dolphin where there is overlap between dolphin habitat and trawl operations. Trawlers are still operating beyond of 1 nautical mile of the coast where dolphins continue to be vulnerable to bycatch.

Marine pollution and debris

Dolphins like Maui's which inhabit shallow coastal waters are vulnerable to the pollutants which humans allow into the sea. Chemicals from industrial waste, stormwater and agricultural runoff like PCBs, DDT, dioxins and metals have been found in Hector's dolphin's blubber (including Maui's dolphins).

These pollutants bio-accumulate, which means they increase in potency as they move up the food chain. Maui's dolphins are near the top of their food chain and these pollutants can be passed on to young dolphins through their mother's milk. High levels of exposure can cause loss of fertility and compromise immune systems in marine mammals. Another form of pollution which threatens Maui's dolphins is solid rubbish such as plastic shopping bags which can be mistaken for squid and ingested, killing the dolphin.

Boat strikes

The propellers of motor boats pose a risk to Maui's dolphins. Dolphin can suffer skin surface cuts to severe injuries from propellers. For example, in Akaroa Harbour, South Island, a Hector's dolphin calf died due to the direct impact of a boat strike.

Genetic bottleneck

The genetic diversity of Maui's dolphin has declined significantly over the last 100 years, raising concerns about a "genetic bottleneck". Their genetic diversity has been reduced from at least three lineages to one, making them susceptible to extinction from environmental and demographic change.