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 )
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:
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
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 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 (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 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:
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
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.
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 ; tactile ; acoustic ; ultrasound ; echolocation ; vibrations ; chemical ; magnetic
The etymology of the subspecies, Cephalorhychus hectori maui, is based on a Maori legend about a man who, while fishing, pulled up the North Island, Te Ika a Maui.
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 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); sexual ; 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
Hector's dolphin (Cephalorhynchus hectori) is one of four dolphin species belonging to the genus Cephalorhynchus. Hector's dolphin is the only cetacean endemic to New Zealand, and comprises two subspecies: C. h. hectori, the more numerous subspecies, also referred to as South Island Hector's dolphin; and the critically endangered Māui dolphin (C. h. maui), found off the West Coast of the North Island.[3]
Hector's dolphin was named after Sir James Hector (1834–1907), who was the curator of the Colonial Museum in Wellington (now the Museum of New Zealand Te Papa Tongarewa). He examined the first specimen of the dolphin found by cephologists. The species was scientifically described by Belgian zoologist Pierre-Joseph van Beneden in 1881. Māori names for Hector's and Māui dolphin include tutumairekurai, tupoupou and popoto.
Hector's dolphin is the smallest dolphin species. Mature adults have a total length of 1.2–1.6 m (3 ft 11 in – 5 ft 3 in) and weigh 40–60 kg (88–132 lb).[4] The species is sexually dimorphic, with females being about 5–7% longer than males.[5] The body shape is stocky, with no discernible beak. 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 back and sides are predominantly light grey, while the dorsal fin, flippers, and flukes are black. 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. A subtly shaded, crescent-shaped black band crosses the head just behind the blowhole. The throat and belly are creamy white, separated by dark-grey bands meeting between the flippers. A white stripe extends from the belly onto each flank below the dorsal fin.
At birth, Hector's dolphin calves have a total length of 60–80 cm (24–31 in) and weigh 8–10 kg (18–22 lb).[6] Their coloration is the almost same as adults, although the grey has a darker hue. Newborn Hector's dolphins have distinct fetal fold marks on their flanks that cause a change in coloration pattern of the skin. These changes are visible for approximately six months and consist of four to six vertical light grey stripes against darker grey skin.[6]
Data from field studies, beachcast individuals, and dolphins caught in fishing nets have provided information on their life history and reproductive parameters.[4] Photo-ID based observations at Banks Peninsula from 1984 to 2006 show that individuals can reach at least 22 years of age.[7] Males attain sexual maturity between 6 and 9 years old and females begin calving between 7 and 9 years old. Females will continue to calve every 2–3 years, resulting in a maximum of 4–7 calves in one female's lifetime. Calving occurs during the spring and summer.[8] Calves are assumed to be weaned at around one year of age, and the mortality rate in the first 6 months was estimated to be around 36%.[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).[13][14][11] Hector's dolphins display a seasonal inshore-offshore movement; favouring shallow coastal waters during spring and summer, and moving offshore into deeper waters during autumn and winter. They have also been shown to return to the same location during consecutive summers, displaying high foraging site fidelity. The inshore-offshore movement of Hector's dolphins are thought to relate to seasonal patterns of turbidity and the inshore movements of prey species during spring and summer.[15][11]
Hector's dolphins are generalist feeders, with prey selection based on size (mostly under 10 cm in length) rather than species, although spiny species also appear to be avoided.[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.[16] The stomach contents of dissected dolphins include a mixture of surface-schooling fish, midwater fish, squid, and a variety of benthic species.[16] The main prey species in terms of mass contribution is red cod, and other important prey include Peltorhamphus flatfish, ahuru, New Zealand sprat, Nototodarus arrow squid, and juvenile giant stargazer.[16][15][17]
The remains of Hector's dolphins have been found in the stomachs of broadnose sevengill shark (considered to be their main predator),[11] great white shark and blue shark.[18][19] Unconfirmed predators of Hector's and Māui dolphins include killer whales (orca), mako sharks and bronze whaler shark.[20]
Hector's dolphins preferentially form groups of less than 5 individuals, with a mean of 3.8 individuals, that are highly segregated by sex. The majority of these small groups are single sex. Groups of greater than 5 individuals are formed much less frequently. These larger groups,>5, are usually mixed sex and have been shown to form only to forage or participate in sexual behavior. Nursery groups can also be observed and are usually all female groups of less than 7 mothers and young.[5]
This species has been found to be show a high level of fluidity with weak inter-individual associations, meaning they do not form strong bonds with other individuals. Three types of small preferential groups have been found: nursery groups; immature and subadult groups; and adult male/female groups. All of these small groups show a high level of sex segregation. Hector's dolphins display a sex-age population group composition, meaning they group by biological sex and age.[9]
Males of the species have extremely large testes in proportion to body size, with the highest relative weight in one study being 2.9% of body weight. Large testes in combination with males' smaller overall body size suggests a promiscuous mating system. This type of reproductive system would involve a male attempting to fertilize as many females as possible and little male-male aggression. The amount of sexual behavior per individual in the species is observed most when small single sex groups form large mixed sex groups. Sexual behavior in the species is usually non-aggressive.[8]
Similar to the hourglass dolphin, Hector's dolphins use high-frequency echolocation clicks. However, the Hector's dolphin produces lower source-level clicks than hourglass dolphins due to their crowded environment. This means they can only spot prey at half the distance compared to an hourglass dolphin.[21] The species has a very simple repertoire with few types of clicks, as well as little audible signals in addition to these. More complex clicks could be observed in large groups.[22]
Hector's and Māui dolphins are endemic to the coastal regions of New Zealand. The Hector's dolphin sub-species is most abundant in discontinuous regions of high turbidity around the South Island. They are most abundant off the East Coast and West Coast, most notably around Banks Peninsula, with smaller, more isolated populations off the North Coast and South Coast (notably at Te Waewae Bay).[23][24] Smaller populations are scattered around the South Island, including: Cook Strait, Kaikoura, Catlins (e.g., Porpoise Bay, Curio Bay), and Otago coasts (e.g.Karitane, Oamaru, Moeraki, Otago Harbour, and Blueskin Bay).[25] Māui dolphin are typically found on the west coast of the North Island between Maunganui Bluff and Whanganui.[26]
An aerial survey of South Island Hector's dolphin abundance—which was commissioned by the Ministry for Primary Industries, carried out the Cawthron Institute, and endorsed by the International Whaling Commission—estimated a total population size of 14,849 dolphins (95% confidence interval = 11,923–18,492).[27] This was almost twice the previous, published estimate from earlier surveys (7,300; 95% CI 5,303–9,966). 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 is 63 individuals of age 1 year or older (95% CL = 57, 75).[29]
Occasionally, South Island Hector's dolphins (determined from genetics) are found around the North Island, up to Bay of Plenty or Hawke's Bay.[30] In 2012, a genetic analysis of tissue samples from dolphins in the core Maui dolphin range, including historical samples, revealed the presence of at least three South Island Hector's dolphins off the West Coast of the North Island (two of them alive), along with another five South Island Hector's dolphins sampled between Wellington and Oakura from 1967 to 2012.[31]
Previously, the deep waters of the Cook Strait were considered to be an effective barrier to mixing between the South Island Hector's and North Island Māui sub-species for around 15,000 and 16,000 years. This is coincident with the separation of the North and South Islands of New Zealand at the end of the last ice age.[32] To date, there is no evidence of interbreeding between South Island Hector's dolphin and Māui dolphin,[31][33] but it is likely they could given their close genetic composition.
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.[34] Death is ultimately caused by suffocation, although injury and sub-lethal effects can also result from the mechanical abrasion of fins resulting from entanglement. Since the 1970s, gillnets have been made from lightweight monofilament, which is difficult for dolphins to detect. 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.[35]
Deaths in fishing nets were previously considered to be the most serious threat (responsible for more than 95% of the human-caused deaths in Māui dolphins), with currently lower level threats including tourism, disease, and marine mining.[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.[38] Population simulations estimated that the current population is 30% of the 1970 population size estimate of 50,000 dolphins, based on their estimated capture rate in commercial gillnet fisheries.[39]
The latest government-approved estimates of annual deaths in commercial gillnets (for the period from 2014/15 to 2016/17) was 19–93 South Island Hector's dolphins and 0.0–0.3 Māui dolphins annually.[11] The low estimate for Māui dolphin deaths in gillnets is consistent with the lack of any observed captures in commercial setnets off the West Coast of the North Island since late-2012, despite 100% observer coverage in this fishery across this time period. Annual deaths in commercial trawls were estimated to be 0.2–26.6 Hector's dolphins and 0.00–0.05 Maui dolphins (from 2014/15 to 2016/17). Based on these levels of mortality, the increased abundance of Hector's dolphins and faster population growth potential than previously thought, the commercial fishery threat (alone) would be unlikely to prevent population recovery to at least 80% of unimpacted levels, for either Hector's or Māui dolphins.[11] However the threat from commercial fishing was estimated to be higher for some regional populations relative to others, e.g., East Coast South Island, and may have a greater effect on certain smaller populations, e.g., Hector's dolphins along the Kaikoura Coast.[11]
The first marine protected area (MPA) for Hector's dolphin was designated in 1988 at Banks Peninsula, where commercial gill-netting was effectively prohibited out to 4 nmi (7.4 km; 4.6 mi) offshore and recreational gill-netting was subject to seasonal restrictions. A second MPA was designated on the west coast of the North Island in 2003. Populations continued to decline due to by-catch outside the MPAs.[26]
Additional protection was introduced in 2008, banning gill-netting within 4 nautical miles of the majority of the South Island's east and south coasts, out to 2 nautical miles (3.7 km) offshore off the South Island's west coast and extending the gillnet ban on the North Island's west coast to 7 nmi (13 km; 8.1 mi) offshore. Also, restrictions were placed on trawling in some of these areas. For further details on these regulations, see the Ministry of Fisheries website.[40] Five marine mammal sanctuaries were designated in 2008 to manage nonfishing-related threats to Hector's and Māui dolphins.[41] Their regulations include restrictions on mining and seismic acoustic surveys. Further restrictions were introduced into Taranaki waters in 2012 and 2013 to protect Māui dolphins.[42]
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.
The unicellular parasiteToxoplasma gondii is considered to be the main non-fishery cause of death. 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).[43] The same study found that approximately two-thirds of dolphins had previously been infected with the toxoplasma parasite. An update to this study found that toxoplasmosis had killed nine out of 38 post-weaning age Hector's and Māui dolphins found washed up or floating at-sea, and that were not too autolised to determine a cause of death.[44] Of these nine, six were reproductive females, tentatively indicating that this demographic may be more susceptible to infection.[11] In New Zealand, the domestic house cat is the only known definitive host for toxoplasma, and Hector's and Maui dolphins are thought to become infected as a result of their preference for turbid coastal waters near river mouths, where toxoplasma oocyst densities are likely to be relatively high.[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.[45] Brucellosis has been determined from necropsies to have killed both Hector's and Māui dolphins and to have caused reproductive disease, indicating that it may affect the reproductive success of both sub-species.[46][11]
The high levels of sex segregation and fragmentation of different populations in Hector's dolphin have been discussed as contributing to the overall population decline, as it becomes more difficult for males to find a female and copulate. The Allee effect begins to occur when a low-density population has low reproductive rates leading to increased population decline.[5] In addition, low gene flow between populations may result from this species' high foraging site fidelity. Hector's dolphins have not been found to participate in alongshore migrations, which may also contribute to their lack of genetic diversity.
Samples from 1870 to today have provided a historical timeline for the species' population decline. Lack of neighboring populations due to fishery-related mortality has decreased gene flow and contributed to an overall loss in mitochondrial DNA diversity. As a result, the populations have become fragmented and isolated, leading to inbreeding. The geographical range has been lessened to the point where gene flow and immigration may no longer be possible between Māui dolphin and Hector's dolphin.[38][47]
Potential interbreeding between Hector's and Māui dolphins could increase the numbers of dolphins in the Māui range and reduce the risk of inbreeding depression, but such interbreeding could eventually result in a hybridisation of the Māui back into the Hector's species and lead to a reclassification of Māui as again the North Island Hector's. Hybridisation in this manner threatens the Otago black stilt[48] and the Chatham Islands' Forbes parakeet[49] and has eliminated the South Island brown teal as a subspecies.[50] Researchers have also identified potential interbreeding as threatening the Māui with hybrid breakdown and outbreeding depression.
{{cite web}}: CS1 maint: url-status (link) {{cite web}}: CS1 maint: url-status (link) {{cite web}}: CS1 maint: url-status (link) {{cite web}}: CS1 maint: url-status (link) Hector's dolphin (Cephalorhynchus hectori) is one of four dolphin species belonging to the genus Cephalorhynchus. Hector's dolphin is the only cetacean endemic to New Zealand, and comprises two subspecies: C. h. hectori, the more numerous subspecies, also referred to as South Island Hector's dolphin; and the critically endangered Māui dolphin (C. h. maui), found off the West Coast of the North Island.
