Hector’s dolphins are the smallest of the world's cetaceans and exhibit sexual dimorphism, with females being larger than males. Adult males (males who are 8 years of age and older) along the South Island coast, are on average 125 cm in total length, measured from snout to tail notch, and can grow up to 144 cm in total length. Adult, South Island females are on average 136.6 cm in total length and can grow up to 153 cm. North Island males can grow up to 146 cm in total length, and females can grow up to 162.5 cm. North Island dolphins are significantly longer than their South Island counterparts. Adults can weigh between 50 to 60 kg.
At birth, Hector’s dolphins are thought to be between 75 and 80 cm. Individuals less than 1 year old range in size from 76.6 to 99 cm in total length, while individuals between 2 and 3 years old are between 104.6 and 119 cm in total length. Individuals 3 years and older are harder to place into specific age classes, as body length becomes more variable. Growth rates significantly decrease by 5 years of age .
Dolphins and other odontocetes have one set of teeth over their lifespan. Number of teeth can vary across individuals. However, Hector’s dolphins can have as many as 31 teeth on both sides of the upper and lower jaws. Their teeth are conical and can be up to 13 mm in length and 3 mm in diameter at its widest point.
North Island Hector’s dolphins, or Maui’s dolphins, are distinct from those found along the South Island coast. Historically, North Island individuals have had only three mtDNA lineages, and those alive today only have one. In comparison, the South Island population has as many as 16 different mtDNA lineages. The single mtDNA lineage that remains in the North Island population differs from those in the South Island by a single, diagnostic nucleotide substitution. In addition to significant genetic differences, the North and South Island populations exhibit significant differences in morphology. Most notably, North Island dolphins have larger skulls than South Island dolphins. Minor morphological differences exist between the three South Island populations.
From birth to around 6 months old, Hector’s dolphins have light grey stripes on their flanks, caused by fetal fold marks, which stand out from the rest of the dark-gray body. Color patterns around the genital slit of adults are sexually dimorphic. South Island males have an elongated black patch around the genital slit which is heart-shaped. In contrast, North Island dolphins have a reduced genital patch, or no patch at all. The beaks of Hector’s dolphins are not easily distinguished from the head. Their dorsal fin is unusual compared to other delphinids, having a rounded or lobed appearance. The body of Hector’s dolphins is predominantly light grey. Except for a black patch that runs between the flippers, their ventral surface is white. They have a white band that runs along their sides, extending towards the posterior end, outlined by dark-grey. The dorsal fin, flippers, flukes, beak tip, blow hole area, and sides of the face are dark grey to black, with much of the chin and lower jaw being white.
Range mass: 50 to 60 kg.
Range length: 120 to 162.5 cm.
Average length: 136.6 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: female larger; sexes colored or patterned differently