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. (Baker, et al., 2002; Brager, 1999; Dawson, et al., 2001; King and Brooks, 2004; Martien, et al., 1999; Pichler, et al., 1998; Rayment, et al., 2009; Slooten, et al., 2006; Slooten, et al., 2004; Slooten, et al., 1993)
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. (Brager, et al., 2002; King and Brooks, 2004; Pichler, et al., 1998; Slooten, et al., 2006)
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. (Brager, 1999; Dawson and Slooten, 1993; Slooten, 1991)
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 . (Slooten, 1991)
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. (Slooten, 1991)
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. (Baker, et al., 2002; Dawson, et al., 2001; Pichler, et al., 1998)
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. (Baker, et al., 2002; Jefferson, et al., 2008; Slooten, 1991)
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. (Slooten, 1991; Slooten, 1994; Slooten, et al., 1993)
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. (Slooten, 1994; Slooten, et al., 1993)
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. (Brager, et al., 2002; Dawson and Slooten, 1993; Slooten, 1991; Slooten, et al., 1993)
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. (Brager, 1999; Dawson, 1991; Slooten, 1991)
The average lifespan of Hector's dolphins has not been documented. However, the oldest recorded individual was 20 years old at time of capture. (Slooten, 1991)
Hector’s dolphins live in fission-fusion social groups, which are common in many cetaceans. Males and females have a large number of weak associations with many other individuals. They are commonly found in groups of 2 to 8, which join, and subsequently part ways, with other groups. Groups that form temporary associations with other groups are often in close proximity to each other. Association among individuals tends to last no longer than a few days. (Brager, 1999; Slooten, et al., 1993)
Aggression in Hector’s dolphins is expressed via tail-splashing, chasing, biting, and bubble-blowing. Breaching, which is often done when feeding, appears to be associated with a state of excitement. In addition, lobtailing is associated with excitement and sometimes aggression. Dolphins often flex their body at the water surface and swim on their sides during feeding. Hector’s dolphins are slow swimmers relative to other delphinids and use an undulating motion to move through the water. Dives usually last less than 3 minutes. Hector’s dolphins tend to swim closer together when in close proximity to boats, which may be an indication of stress. (Bejder, et al., 1999; Coffey, 1977; Slooten, 1994)
The home range of Hector's dolphins often overlaps with those of nearby groups. They exhibit fairly strong site fidelity and move only short distances from their natal range. The longest alongshore distance recorded was 106 km. All other documented movements have been less than 60 km, with an average of 31 km. Each social group has a distinct core use area. There is little movement between these core areas, which tend to be about 30 km apart. Geographic separation between core use areas may have lead to genetic isolation between local populations. Similar to other marine mammals, dolphins are commonly observed foraging, socializing, and nursing their young in shallow inshore waters. (Brager, et al., 2002; Brager, 1999; Dawson, et al., 2001; Pichler, et al., 1998; Rayment, et al., 2009)
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. (Thorpe, et al., 1991)
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. (Brager, 1998; Brager, 1999; Jefferson, et al., 2008; Pichler, et al., 1998; Rayment, et al., 2009; Slooten, et al., 2006; Thorpe, et al., 1991)
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. (Dawson and Slooten, 1993; Rayment, et al., 2009)
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. (Brager, 1998; Rayment, et al., 2009; Stockin, et al., 2010)
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. (Bejder, et al., 1999; Rayment, et al., 2009)
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. (Dawson, 1991)
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. (Bejder, et al., 1999; Dawson, et al., 2001; Martien, et al., 1999; Rayment, et al., 2009; Slooten and Lad, 1991; Slooten, 1994; Stockin, et al., 2010)
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. (Brager, et al., 2002; Dawson, 1991; Martien, et al., 1999; Slooten, et al., 2006)
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. (Brager, et al., 2002; Dawson, et al., 2001; Dawson, 1991; Rayment, et al., 2009; Slooten and Lad, 1991; Slooten, et al., 2006; Slooten, 1991)
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. (Stockin, et al., 2010)
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. (Baker, et al., 2002)
Linda Lees (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, John Berini (editor), Special Projects.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
(as perception channel keyword). This animal has a special ability to detect the Earth's magnetic fields.
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats fish
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
uses sound above the range of human hearing for either navigation or communication or both
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
young are relatively well-developed when born
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