Māui's Dolphin

## About

A Māui's dolphin breaching

The Māui's dolphin ***(Cephalorhynchus hectori maui)*** is a subspecies of the hector's dolphin and is also one of New Zealand's only native mammals. Recognised as a distinct subspecies of the Hector's dolphin ***(Cephalorhynchus hectori maui)*** in 2002 by new Zealand scientist Dr. Alan Baker, the Māui's dolphin was originally known as the North Island Hector's dolphin until it was proven to be its own subspecies. The Māui's dolphin still resembles a Hector's dolphin in appearance despite its genetic distinction. Both species have silver dorsums white underbellies and black markings on their face, caudal and pectoral fins. Both species also have rounded dorsal fins, which are unique to the species among most dolphin species. Though similar, the Māui's dolphin does have distinguishing features, most notably the Māui's dolphin has a noticeably larger skull as well as a wider and longer rostrum (snout). The Māui's dolphin measures to a length of 1.5m (4.9ft) and weighs around 50kg (110lbs), it is just bigger than the Hector's dolphin in terms of size.

## Diet

As Māui's dolphins are obligate carnivores they prey upon animals such as fish like red codling ***(Pseudophycis bachus)***, āhuru flatfish ***(Auchenoceros punctatus)***, stargazer species and sprat. Māui's dolphins occasionally eat arrow squid ***(Loligo plei)*** as well. This diet may also differ regionally between populations and individuals, as the species that the dolphin is suspected to eat, have only been recorded in the stomachs of three deceased individuals.

## Conservation Status

The Māui's dolphin is currently classed as critically endangered by the IUCN however, the IUCN page for the species requires revision, so it will not be used further as a source for this article. Similarly to most threatened cetaceans, Māui's dolphins are most endangered by the use of gillnets in their range. Dolphins can often become ensnared in the nets, which results typically in drowning. The reasoning for the continued entrapment among the species, is that the dolphins are typically found in extreme proximity to human cities. In particular, the Māui's dolphin occurs close to Auckland, New Zealand's most populated city. Māui's dolphins may also approach harbours, which can lead to accidental casualties. Apart from gillnet fishing, dolphins are also face threats from various types of pollutants. Oil spills are suspected to be extremely damaging to the health of individuals, as the hydrocarbons found in oils and the gases they harbour may cause cancer or premature death in dolphins. Similarly, metals such as mercury pose an issue for the species as they do not deteriorate and instead accumulate over time. Large quantities of these metals may be toxic to the Māui's dolphins however, Cetacean risk form metallic intoxication is typically understudied and is unquantified in Māui's dolphins according to the New Zealand Department of Conservation. Through pathogens caused by factors such as farm and freshwater run off, can cause sickness in individuals. Particularly, sewer outfalls and shipping can cause pathogens that are attributed to dolphin casualties caused by disease. These diseases can typically cause abortion in both the Māui's and Hector's dolphins. Specifically two main diseases have been causing these abortions and casualties within the populations. Toxoplasma oocysts, is one of these diseases and it is transmitted most often by the domestic cat and it causes premature casualties most often in reproductive females. It is believed that the Toxoplasmosis parasites are transferred to the dolphins through freshwater run off, after contact with the feces of the previous host. These parasites will eventually move up the food chain, reaching the dolphins. The second disease is Brucellosis. Brucellosis is a bacterial infection that was found to be active in the body of a deceased male dolphin in 2006. Brucellosis could prove to be a massive threat to the tiny Māui's dolphin population, as the disease has been proven to cause abortion in late stage pregnancy for terrestrial mammals. Brucellosis does effect Cetaceans, meaning that it could possibly spell disaster for the reproductive efforts of the Māui's dolphin. The most problematic form of pollution for the species is plastic debris. Plastic debris such as garbage or fishing equipment can entangle individuals, causing mass casualties. A small portion of the Māui's dolphin's available range was protected on the 1st of October 2020. These protections included the introduction of new anti-gillnetting and fishing measures on the coasts of New Zealand. The ban also expanded upon the initial trawling bans in the Central Māui's dolphin habitat. Unfortunately these bans may not be enough to recover the species dwindling population. WWF itself has supported this sentiment by exclaiming that; all human related threats of the species must be reduced by 50-75% within the following ten years, to ensure the safety of the species. Many fear that this goal is unachievable.

## Range and Population

Māui's dolphins only occur on the western coast of North Island, New Zealand. The dolphins are most frequently found in coastal area, typically in shallow waters. Māui's dolphins particularly favour waters with high turbidity. Comparatively to the range of the Hector's dolphin, the Māui's dolphin is found in far fewer locations. Despite their more sparse range, distribution of the Māui's dolphin overlaps with the Hector's dolphin population, specifically off the coasts of western North Island. Though the distribution of the Māui's dolphin is now restricted to the western coast of North Island, previous reports of the species being found on the east coast suggest that the Māui's dolphin distribution has become severely reduced, leading to its regional extinction in eastern North Island. The Māui's dolphin population is known to be extremely low, sitting at around 63 individuals over the age of one. This population estimate makes Māui's dolphins the rarest and most endangered oceanic dolphin species.

## Behaviour

Māui's dolphins use echolocation to navigate their habitat, as do all odontocetes. Māui's dolphins will typically produce high pitched clicks while using echolocation however, these sounds are also emitted as a form of long distance communication between individuals. These clicks are actually so high-pitched, that the human ear cannot interoperate them, measuring to a pitch of 125Hz. Similarly to Hector's dolphins, Māui's dolphins are one of the more expressive Cetaceans, conveying ranges of emotion through body language. For example tail-smacking and breaching is typically a sign of excitement or playfulness. Māui's dolphins are also quite social, -being found in pods of up to 14 individuals- and will commonly participate in playful behaviour with one another. Māui's dolphins have been observed playing with items such as seaweed for entertainment as well as blowing bubbles for each other and play fighting. Despite being found most prolifically in male-female mixed pods, after a calf is born females may create nursery pods, consisting solely of females. These pods are typically created separately to regular pods as males have no role in the rearing of their offspring.

### Relationship with Humans

The relationship between the Māui's dolphin and humans has existed even before European settlements existed in New Zealand. Māui's dolphins are actually named after the Māori demigod Māui. the reasoning for the relation between the dolphins and the demigod is that of the shared relationship the two have surrounding North Island. The role that Māui plays in New Zealand mythology cannot be explained in this article in its full state however, to understand the naming of the dolphin species, we must review the story of North Island. The legend states that Māui and his brothers were fishing on their canoe (South island) and they caught a fish (North Island). Whilst Māui was not paying attention, his brothers began fighting and chopped up the fish. This fish would become to be known as Te Ika-a-Māui, meaning "The fish of Māui". Due to the legend, upon the discovery of the Māui's dolphin's genetic distinction from the Hector's dolphin, it was named after Māui for its geographic distribution off the coasts of North Island. In the modern day the relationship between the Māui's dolphin and humans is much more complicated, as humans now pose a major threat to the species. As a result of living in harbours as well as proximity to oil/gas drilling and marine construction, Māui's dolphins often become victims of noise pollution. Noise pollution poses a major threat to the species as a whole, as it can damage the hearing ability of individuals as well as make it hard for them to hunt via echolocation in high traffic coastal regions. Evidence towards the accidental collision of Māui's dolphins and vessels has also been found, in the form of an individual who was found to have healed scars from a boat propeller, found off the coast of Bethell's beach. Tourism has also been found to have long term effects on the species, possibly reducing breeding success, feeding and available areas for the species to be left alone to relax. Due to the strain of tourism, many Māui's dolphins opt to leave heavily populated areas in general, in order to find tranquility in quieter waters. Drilling operations for the retrieval of valuable gases and oil as well as mineral mining, has become a major problem for the species in particular, as it interferes with the species ability to navigate, hunt and communicate. Far more pressingly, these operations can also lead to a shortage of food for the species, as fish and squid evacuate the area of operation.

## In Captivity

Due to the current issues raised in captivity surrounding Cetacean welfare, no Māui's dolphins exist in captivity.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/39427/44200192
* Facts About Hector's and Māui dolphins | New Zealand Department of Conservation - https://www.doc.govt.nz/nature/native-animals/marine-mammals/dolphins/maui-dolphin/facts/
* Threats Caused by People | New Zealand Department of Conservation - https://www.doc.govt.nz/nature/native-animals/marine-mammals/dolphins/maui-dolphin/threats/threats-caused-by-people/
* The critically endangered Māui dolphin is a conservation priority – we shouldn’t let uncertainty stop action to save it | The Conversation - https://theconversation.com/the-critically-endangered-maui-dolphin-is-a-conservation-priority-we-shouldnt-let-uncertainty-stop-action-to-save-it-167987
* Māui dolphin | Wikipedia - https://en.wikipedia.org/wiki/M%C4%81ui\_dolphin
* North Island | Wikipedia - https://en.wikipedia.org/wiki/North\_Island
* Help Save the Last 63 | WWF - https://www.wwf.org.nz/what\_we\_do/species/hectors\_maui/maui\_dolphin/