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Native animals

Maui's dolphin

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Threats

Threats caused by people

Find out more about threats to Maui's dolphins caused by people.

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Fishing
Pollution
Interactions with boats
Construction in marine areas
Mining
Tourism
Scientific interactions
Climate change

Fishing

Maui's dolphins mostly live within a few miles of the coast and occasionally venture into some harbours, which can result in an overlap with commercial and amateur fisheries. A significant number of Maui's dolphins have died as a result of incidental bycatch in set nets. This has prompted a series of set net restrictions in areas in which the Maui's dolphin is known to range.

While we have no records of Maui's dolphins being caught in trawls, there have been incidents of hector's dolphins caught in trawl nets. Some restrictions also apply to trawling to reduce the risk of this happening. Drift nets are now banned from the lower reaches of the Waikato as the nets were sometimes lost and floated out to sea where they had the potential to catch the dolphins.

Pollution

The fact that Maui's dolphins mostly live within a few miles of the coast exposes them to a variety of pollutants and contaminants including; organochlorines, heavy metals, oil (from oil spills) and plastic debris.

Organochlorines

Organochlorines are known to affect the breeding success of some marine mammal species, in some cases resulting in sterility, and they may suppress the immune system in some species. Recent research shows that while Maui's and Hector's dolphins have high levels of organochlorines, none of the samples tested had levels that were likely to have caused the sort of problems mentioned above.

Metals

Non-essential metals (e.g. mercury, lead and cadmium), which have little or no recorded biological function, can accumulate and are often toxic even at low concentrations. Data on the effects of metal toxicity in cetacean species is sparse, and the risk from metal toxicity is unquantified for Maui's dolphins.

Oil spills

The extraction and transportation of crude oil poses a potential threat for Maui's dolphins. Polycyclic aromatic hydrocarbons such as found in oil and gas compounds have been linked to cancers in some species of marine mammals. The risk from these compounds is unquantified for Maui's dolphins.

Plastic debris

Marine mammals can become physically entangled in loops or openings of drifting plastic debris. Entangled animals may suffer impaired ability to catch food or avoid predators. They may also incur wounds and infections from the abrasive or cutting action of debris. Plastic ingestion could pose a threat to the dolphins. The risk is unquantified for Maui's dolphins.

Interactions with boats

Vessel traffic (for example, recreational boating or commercial vessel traffic) can potentially result in boat strike or disturbance of Maui's dolphins. There is a record of one Maui's dolphin beachcast at Bethells Beach with old scars from a propeller strike.

Construction in marine areas

Because of the mainly coastal distribution of Maui's dolphins, coastal works and development have the potential to negatively impact on aspects of the dolphin's ecology. These activities may displace the dolphins from important habitat, as well as potentially impact on predator-prey relationships, foraging success and reproductive success.

Mining

Seabed mining and exploration including seismic testing is likely to have an impact on Maui's dolphins. Potential impacts include:

Disturbance of seafloor with benthic communities.
Avoidance of the area by Maui's dolphins because of noise production and the presence of vessels.
Discharge plumes and suspended sediments interfering with photosynthetic, filtering, feeding and respiratory functions of marine organisms.
Avoidance of the area by fish species, leading to a loss of food sources for Maui's dolphins.
Changes in bathymetry and bottom type may also cause alterations in population and migration patterns.

The information currently available is inadequate to allow any conclusions to be drawn about threats posed by offshore mining, beyond suggesting that a potential for adverse impacts exists.

Tourism

Maui's dolphins are likely to be affected by dolphin watching operations. Although it appears that single encounters with a boat or a group of swimmers are unlikely to cause major disturbance for Maui's dolphins, cumulative effects of multiple and extended encounters could have detrimental consequences.

Long-term effects of encounters may, for example, reduce breeding success, feeding activity, and resting opportunities, and these could result in displacement of individuals from an area. The effects of tourism on marine mammals are well understood and have been studied in many dolphin species including Hector's dolphins around Banks Peninsula.

Scientific interactions

Research on Maui's dolphins can potentially generate a threat to the dolphins themselves. This could include tagging (including satellite or other transmitters), taking biopsy samples, or through harassment. These risks are minimised by careful research design.

Climate change

Research into the potential impacts of climate change on migratory species (including marine mammals) identified a number of possible future effects. The study concluded that the greatest threat to marine mammals probably comes from changes in their food resources as a result of climate change.