The most distinctive feature is the rounded dorsal fin, with a convex trailing edge and undercut rear margin.

The overall coloration appearance is pale grey, but closer inspection reveals a complex and elegant combination of colours.

The eyes are surrounded by a black mask, which extends forward to the tip of the rostrum and back to the base of the flipper.

Newborn Hector's dolphins have distinct fetal fold marks on their flanks that cause a change in coloration pattern of the skin.

[6] Data from field studies, beachcast individuals, and dolphins caught in fishing nets have provided information on their life history and reproductive parameters.

[9] These combined life-history characteristics mean that, like many other cetaceans, Hector's dolphins are only capable of slow population growth.

Their maximum population growth rate was previously estimated to be 1.8–4.9% per year, based on old demographic information,[10] which was then updated to 3–7% per year, based on updated demographic information and a life history invariant observed across all vertebrates [11][12] The species' range includes murky coastal waters out to 100 m (330 ft) depth, though almost all sightings are in waters shallower than 50 m (160 ft).

[16] The largest prey item recovered from a Hector's dolphin stomach was an undigested red cod weighing 500 g with a standard length of 35 cm.

[5] This species has been found to show a high level of fluidity with weak inter-individual associations, meaning they do not form strong bonds with other individuals.

[dubious – discuss] This type of reproductive system would involve a male attempting to fertilize as many females as possible and little male-male aggression.

[25] Māui dolphin are typically found on the west coast of the North Island between Maunganui Bluff and Whanganui.

This difference was primarily due to a much larger estimated population along East Coast, which was distributed further offshore than previously thought.

[28] The latest estimate of the Māui dolphin subspecies 2020–2021 is 54 individuals aged 1 year or older (1+) (95% confidence interval (CI) = 48–66).

Hector's and Māui dolphin deaths occur as a direct result of commercial and recreational fishing due to entanglement or capture in gillnets or trawls.

Hector's dolphins are actively attracted to trawling vessels and can frequently be seen following trawlers and diving down to the net, which could result in the unwanted bycatch.

[36][37] Research of decreases in mitochondrial DNA diversity among hector's dolphin populations has suggested that the number of gill-net entanglement deaths likely far surpasses that reported by fisheries.

[42] The Banks Peninsula Marine Mammal Sanctuary was expanded in 2020, with restrictions introduced on seismic surveying and seabed mining.

[43] The Scientific Committee of the International Whaling Commission has recommended extending protection for Māui dolphin further south to Whanganui and further offshore to 20 nautical miles from the coastline.

The IUCN has recommended protecting Hector's and Māui dolphins from gill-net and trawl fisheries, from the shoreline to the 100 m depth contour.

A 2013 study found that seven of 28 beachcast or bycaught Hector's and Māui dolphins died as a result of toxoplasmosis, which had necrotising and haemorrhagic lesions in the lung (n = 7), lymph nodes (n = 6), liver (n = 4) and adrenals (n = 3).

[11] Brucellosis is a notable bacterial disease of Hector's and Māui dolphins that can cause late pregnancy abortion in terrestrial mammals, and has been found in a range of cetacean species elsewhere.

[5] In addition, low gene flow between populations may result from this species' high foraging site fidelity.

Lack of neighboring populations due to fishery-related mortality has decreased gene flow and contributed to an overall loss in mitochondrial DNA diversity.