Hector’s dolphins (Cephalorhynchus hectori) are marine cetaceans endemic to the coastal waters of New Zealand. There are 4 main regional populations of Hector’s dolphins, which are geographically and reproductively isolated from each other. Of the 4 distinct populations of Hector's dolphins, one is found along the west coast of North Island, between Dargaville and New Plymouth. This particular population, referred to as Maui's dolphin, is very small, containing approximately 111 individuals. Their range has greatly declined over the last few decades. On the South Island, there are three populations of Hector's dolphin that are genetically distinct from one another. These populations reside along the west, east and south coasts, excluding Fiordland. The total population of Hector’s dolphins around the South Island was estimated at 7240 individuals in 2004, with 5388 found on the west coast, mostly concentrated between 41º30’S and 44º30’S. Hector’s dolphins are most abundant between Karamea and Makawhio Point on the west coast and around Banks Peninsula on the east coast.

Biogeographic Regions: australian (Native ); pacific ocean (Native )

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

• Marine

Hector’s dolphins inhabit the coastal waters of New Zealand and are typically observed in water less than 90 meters deep. There have been sightings as far as 4 nautical miles off the west coast of North Island, 6 nautical miles off the west coast of South Island, and 15 nautical miles off the east coast of South Island; all of which occurred in water no deeper than 90 meters. Hector’s dolphins are most often observed less than 1 km from the shoreline. During the austral summer, Hector's dolphins prefer to be close to shore. During winter they tend to be more dispersed and are found farther from shore. During spring, they may migrate to different coastal areas or return to the same area as the previous summer.

Range depth: 1 to 90 m.

Habitat Regions: temperate ; saltwater or marine

Aquatic Biomes: coastal

Hector’s dolphins use echolocation to help locate prey in the shallow, turbid, coastal waters they inhabit. They are generalist feeders and primarily prey on small fish and squid. During spring and summer, many prey species come in shore to spawn. It has been suggested that in-shore larvae may be the main reason Hector’s dolphins remain closer to shore during this time of year. Populations along the east coast of South Island have more diverse prey assemblages than those on the west coast. Eight species make up 80% of their diet, while on the west coast only 4 species make up 80% of their diet.

Animal Foods: fish; mollusks

Primary Diet: carnivore (Piscivore )

Hector’s dolphins are near the top of the food chain and likely play an important role in regulating local fish populations. During the spring and summer, white-fronted terns (Sterna striata) feed with Hector’s dolphins, likely as facultative commensalists, by capturing small fish being chased by dolphins.

Commensal/Parasitic Species:

• white-fronted terns (Sterna striata)

Gut-content analysis suggests that sevengill sharks (Notorynchus cepedianus) and blue sharks (Prionace glauca) are major predators of Hector's dolphins. Living in shallow inshore waters may help them avoid potential predators.

Known Predators:

• sevengill sharks (Notorynchus cepedianus)
• blue sharks (Prionace glauca)

Dolphins, like other odontocetes, use echolocation. Hector’s dolphins produce narrow (3dB) bandwidth sounds which range from 7 to 56 kHz. Recordings of high frequency clicks had peak frequencies of 82 to 135 kHz and ranged in length from 80 to 800 microseconds. Most clicks produced by Hector’s dolphins are simple and just over half (52%) have one peak and 40% have two peaks. Research suggests that clicks with one peak are best for determining distance rather than velocity. Clicks with multiple peaks may be used to determine velocities of other animals as well as communicate with other conspecifics. High frequency clicks are audible to humans and are often linked with aerial behavior, which may indicate a state of excitement.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: vibrations

Perception Channels: visual ; acoustic ; ultrasound ; echolocation ; vibrations ; magnetic

The average lifespan of Hector's dolphins has not been documented. However, the oldest recorded individual was 20 years old at time of capture.

Range lifespan

Status: wild: 20 (high) years.

Hector's dolphins are polygynandrous, as both sexes have multiple mates. Males search for receptive females rather than monopolizing access to individual females and aggressiveness is not associated with sexual behavior. Mature males have very large testis relative to their body size, making up as much as 2.9% of total body mass.

Sexual or social behaviors (e.g., presenting one's abdomen or penis and physical contact) are often associated with mating. Hector’s dolphins exhibit increased sexual behavior (per individual per minute) in larger groups then in smaller groups. Sexual behavior is 2 times greater in groups of 11 to 15 individuals than in groups numbering 1 to 5 or 6 to 10, and nearly 20 times higher than in groups of 16 to 20 individuals. The presence of young does not appear to affect sexual behavior.

Mating System: polygynandrous (promiscuous)

Male Hector’s dolphins reach sexual maturity between ages 6 and 9, and females reach sexual maturity between ages 7 and 9. They mate in the summer, have a gestation period between 10 and 12 months, and parturition occurs from early November to mid February. Hector’s dolphins reproduce every 2 to 4 years and usually one calf is born at a time. Females can give birth to a maximum of 7 calves during their lifetime.

Breeding interval: Hector's dolphins reproduce every 2 to 4 years.

Breeding season: Hector's dolphins breed during the austral summer

Range number of offspring: 1 (high) .

Average number of offspring: 1.

Range gestation period: 10 to 12 months.

Range weaning age: 12 to 24 months.

Range time to independence: 1 to 2 years.

Range age at sexual or reproductive maturity (female): 7 to 9 years.

Range age at sexual or reproductive maturity (male): 6 to 9 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average number of offspring: 1.

Mother and calf stay together for 1 to 2 years, during which time the mother does not breed. Females with calves often separate from non-calving individuals and form larger calf-cow groups. Once they reach 2 years old, calves become more independent and have been observed in groups with other juveniles and no adults.

Parental Investment: precocial ; female parental care ; pre-weaning/fledging (Protecting: Female); pre-independence (Protecting: Female); extended period of juvenile learning

According to the IUCN Red List of Threatened Species, North Island Hector's dolphins are "critically endangered" and South Island Hector's dolphins are "endangered". Hector’s dolphins are regularly caught in gillnets, which is by far the greatest threat to their survival. Small population size, segregated genetic groups, and low population growth rates (maximum plausible annual growth rate=1.8%) pose a significant threat to their persistence. Trawl nets, pollution, tourism, boat strikes and possibly mining are also thought to affect Hector's dolphins.

Between 1984 and 1988 a minimum of 230 Hector’s dolphins were killed in gill nets, and the majority of entanglements (91%) occurred during the spring and summer. The majority of by-catch occurs less than 4 nautical miles from shore, in water that less than 20 meters deep. Dolphins under 4 years old, particularly those under 2 years old, are caught in gill nets more often than older individuals. This suggests that younger dolphins may be less able to determine the presence of gill nets, possibly due to immature sonar systems. Dolphins under 2 years of age are usually with their mothers full time, however, after 2 years old they become more independent and may be more susceptible to gill net entanglement.

In 1988, the New Zealand Department of Conservation created the Banks Peninsula Marine Mammal Sanctuary under section 22 of the 1978 Marine Mammal Protection Act. The sanctuary is 1170 km², covering nearly 113 km of coast by prohibiting commercial gill netting within its boundaries year round and amateur gill netting from November to February. During all other months, amateur gill-netters are subject to regulations on where gill nets can be used. Despite this, commercial gill nets have been observed to be located on the sanctuary boundaries and amateur gill nets have been reported inside the sanctuary. In August 2001, a sanctuary on the west coast of North Island was established between Maunganui Bluff and Pariokariwa Point prohibiting gill netting. In 2008, the New Zealand Ministry of Fisheries submitted a proposal prohibiting gill netting along most of the east coast of South Island, 4 nautical miles from shore. Also in 2008, the Minister of Conservation proposed extending the Banks Peninsula Marine Mammal Sanctuary 45 km north and up to 12 nautical miles from shore. However, the Minister's proposal suggested removing gill net restrictions, focusing rather on limiting acoustic disturbances. As of 2009, both proposals were still under judicial review.

Hector’s dolphins are subject to bioaccumulation of PCBs and organochlorine pesticides, including dieldrin, hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) and it’s metabolites (DDE and DDD). Dolphins on the east coast of South Island have 3 times higher concentrations of DDT and metabolites, and exhibit higher PCB levels than those on the west coast of South Island. The percent transfer of DDT and its metabolites from a mother to her fetus is 5.7%, and the transfer of PCBs to the fetus is 4.3%. Although it has not been documented, these numbers likely increase during nursing. Today DDT, DDE and DDD still persist in New Zealand soils, two decades after it was banned in New Zealand in 1989.

US Federal List: no special status

CITES: appendix ii

State of Michigan List: no special status

IUCN Red List of Threatened Species: endangered

Hector's dolphins are frequently caught in gill nets but rarely cause enough damage to prevent re-use. There are no known adverse affects of Hector's dolphins on humans.

Swimming with and watching Hector’s dolphins is a major source of tourism, with up to 31 commercial boat trips occurring each day in Akaroa Harbour. Similar levels of tourism occur at various locations along the South Island coast.

Positive Impacts: ecotourism