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. According to the latest figures from the Department of Conservation four Maui's have been reported dead between November 2006 and March 2007. This dolphin is vulnerable to gill net and trawl fishing, marine pollution and debris, boat strikes and genetic bottleneck.

Set net (gill net) fishing

Injured by entanglement in nylon fishing line. © WWF-Canon/Stephen DAWSON

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 yet harbours 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.

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