About Cephalorhynchus hectori (P.-J.van Bénéden, 1881)
Hector's dolphin, with the scientific name Cephalorhynchus hectori, is the smallest dolphin species. Mature adults measure 1.2–1.6 m (3 ft 11 in – 5 ft 3 in) in total length and weigh 40–60 kg (88–132 lb). This species is sexually dimorphic, with females about 5–7% longer than males. They have stocky bodies, a large fluke relative to their body size, and no noticeable beak. Their most distinctive feature is a rounded dorsal fin with a convex trailing edge and an undercut rear margin. Māui dolphins, a population of this species, tend to be longer than South Island Hector's dolphins. The overall coloration of Hector's dolphins combines grey, white, and black: a black mask surrounds their eyes, and a thin black line runs from the head to the blowhole, while the throat and belly are white and the rest of the body is grey. At birth, Hector's dolphin calves are 60–80 cm (24–31 in) long and weigh 8–10 kg (18–22 lb). Their coloration is almost identical to that of adults, though their grey tone is darker. Newborns have distinct fetal fold marks on their flanks that alter the skin color pattern, remaining visible for roughly six months. These marks are four to six vertical light grey stripes set against darker grey skin. This species lives in murky coastal waters out to 100 m (330 ft) depth, though almost all sightings occur in waters shallower than 50 m (160 ft), and individuals are most often observed around 1000 m from shore. Hector's dolphins make seasonal inshore-offshore movements: they favor shallow coastal waters during spring and summer, and move offshore to deeper waters during autumn and winter, with greater dispersal occurring in winter. They return to the same locations across consecutive summers, showing high foraging site fidelity. This seasonal movement is thought to be linked to seasonal turbidity patterns and the inshore movement of prey species during spring and summer. Hector's dolphins are endemic to coastal regions of New Zealand. South Island Hector's dolphins are most abundant in discontinuous high-turbidity regions around the South Island, with the largest populations off the East Coast and West Coast, most notably around Banks Peninsula. Smaller, more isolated populations live off the North Coast and South Coast, particularly at Te Waewae Bay, and additional smaller populations are scattered around the South Island including Cook Strait, Kaikōura, the Catlins such as Porpoise Bay and Curio Bay, and Otago coasts including Karitane, Oamaru, Moeraki, Otago Harbour, and Blueskin Bay. Māui dolphins are typically found along the west coast of the North Island, between Maunganui Bluff and Whanganui. An aerial survey of South Island Hector's dolphin abundance, commissioned by the Ministry for Primary Industries, carried out by the Cawthron Institute, and endorsed by the International Whaling Commission, estimated the total population size at 14,849 dolphins (95% confidence interval = 11,923–18,492). This estimate was almost twice the size of the earlier published estimate of 7,300 dolphins (95% CI 5,303–9,966). The difference was primarily due to a much larger estimated population along the east coast, which was also found further offshore than previously believed. The latest population estimate for Māui dolphin, published in 2023, puts the total at just 48 individuals.
