Cephalorhynchus hectori (P.-J. van Bénéden, 1881) — Details

White-headed Dolphin learn more about names for this taxon

Overview

Brief Summary

Biology

This dolphin tends to occur in groups of between two to eight individuals. These groups often join together forming larger aggregations and then split up (5). Feeding also occurs in groups and the species takes a variety of fish, squid and some crustaceans (5). Females reach maturity at around 7 to 9 years of age, and males between 6 and 9 years. Courtship behaviour involves close contact, leaping, chasing and belly displays. Calves tend to be born in late spring to early summer and the mother will not conceive again until the calf is fully independent (5). Playing with seaweed, bubble blowing and other 'games' are thought to be important social behaviours (5). Certain sounds produced by this dolphin are also thought to be important in a social context; particularly the complex clicks that are produced in large groups (5).
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Description

Hector's dolphin, one of the rarest and smallest of marine dolphins (6), has a short, stocky torpedo-shaped body, which becomes narrow towards the tail. The beak is short and the rounded snout lacks a melon. The sides and back are light grey, there is a darker stripe along the middle, and the underside is whitish (4). The large tail flukes, flippers and characteristically rounded dorsal fin are all black (5). A black marking extends from the snout back around the eye reaching to the flipper (5). Males and females are generally similar in appearance, but females tend to be slightly longer than males (5). Calves have the same markings as adults but pale lines can be seen on darker areas, and the underside has a yellowish tint (5). The common name of this dolphin refers to the New Zealand zoologist Sir James Hector (5), who first collected the species in 1869 (4).
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Distribution

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 )

  • Baker, A., A. Smith, F. Pichler. 2002. Geographical variation in Hector’s dolphin: recognition of new subspecies of Cephalorhynchus hectori. Journal of the Royal Society of New Zealand, 32/4: 713-727.
  • Brager, S. 1999. Association patterns in three populations of Hector’s dolphin, Cephalorhynchus hectori. Canadian Journal of Zoology, 77: 13-18.
  • Dawson, S., E. Slooten, F. Pichler, K. Russell, C. Baker. 2001. The North Island Hector’s Dolphin is Vulnerable to Extinction. Marine Mammal Science, 17/2: 366-371.
  • King, R., S. Brooks. 2004. A classical study of catch-effort models for Hector’s dolphins. Journal of the American Statistical Association, 99/466: 325-333.
  • Martien, K., B. Taylor, E. Slooten, S. Dawson. 1999. A sensitivity analysis to guide research and management for Hector’s dolphin. Biological Conservation, 90: 183-191.
  • Pichler, F., S. Dawson, E. Slooten, C. Baker. 1998. Geographic isolation of Hector’s dolphin populations described by mitochondrial DNA sequences. Conservation Biology, 12/3: 676-682.
  • Rayment, W., S. Dawson, E. Slooten, S. Brager, S. DuFresne, T. Webster. 2009. Kernel density estimates of alongshore home range of Hector’s dolphins at Banks Peninsula, New Zealand. Marine Mammal Science, 25/3: 537-556.
  • Slooten, E., S. Dawson, H. Whitehead. 1993. Associations among photographically identified Hector’s dolphins. Canadian Journal of Zoology, 71: 2311-2318.
  • Slooten, E., S. Dawson, W. Rayment, S. Childerhouse. 2006. A new abundance estimate for Maui’s dolphin: What does it mean for managing this critically endangered species?. Biological Conservation, 128: 576-581.
  • Slooten, E., S. Dawson, W. Rayment. 2004. Aerial surveys for coastal dolphins: abundance of Hector’s dolphins off the South Island west coast, New Zealand. Marine Mammal Science, 20/3: 477-490.
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Range Description

Hector’s Dolphin is endemic to New Zealand, and it has one of the most restricted distributions of any cetacean (Dawson and Slooten 1988; Dawson 2002). They are most common off the South Island and the west coast of the North Island. There are at least three genetically separate populations in the South Island, and a single small North Island population (C. h. maui - Baker et al. 2002).

The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states.
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Range

Endemic to New Zealand waters, this species is found on the west and east coasts of South Island, and only in a very small area off the west coast of North Island (5). Following surveys carried out in 1984 - 1985 the total population was estimated at 3-4,000 individuals, only around 2,000 of which were mature (2).
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Physical Description

Morphology

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

  • Dawson, S., E. Slooten. 1993. Conservation of Hector’s dolphins: The case and process which led to the establishment of the Banks Peninsula Marine Mammal Sanctuary. Aquatic Conservation: Marine and Freshwater Ecosystems, 3/3: 207-221.
  • Jefferson, T., M. Webber, R. Pittman. 2008. Marine Mammals of the World: A comprehensive Guide to their Identification. San Diego, CA: Academic Press, Elsevier.
  • Slooten, E. 1991. Age, growth, and reproduction in Hector’s dolphins. Canadian Journal of Zoology, 69: 1689-1700.
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Ecology

Habitat

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

  • Brager, S., S. Dawson, E. Slooten, S. Smith, G. Stone, A. Yoshinaga. 2002. Site fidelity and along-shore range in Hector’s dolphin, an endangered marine dolphin from New Zealand. Biological Conservation, 108: 281-287.
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Habitat and Ecology

Habitat and Ecology
The habits and biology of Hector's dolphin have been well studied in the last couple of decades, and this is undoubtedly the best-known species of the genus (Dawson 2002). It is found in shallow coastal waters, almost always within about 15 km of shore and <100 m deep, strongly concentrated in shallow, turbid waters close to shore in summer months and dispersing more widely in winter (Slooten et al. 2006a). Photo-identification studies have demonstrated that at least some individuals are resident in small areas (about 30 km of coastline) year-round (Slooten et al. 1993). No two sightings of an individual have been more than 106 km apart (Bräger et al. 2002).

Hector's dolphins feed on several species of small fish and squid (Dawson 2002). The diet is more varied on the east coast of the South Island (8 species make up 80% of the diet) than on the west coast (only 4 species make up 80%).

Systems
  • Marine
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in shallow coastal waters
  • UNESCO-IOC Register of Marine Organisms
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Inhabits coastal waters such as river mouths and shallow bays (7). They very rarely venture further out than 9 km from the coast (4). They prefer shallow waters and may enter estuaries and swim slightly upriver (6)
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Trophic Strategy

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 )

  • Brager, S. 1998. Feeding associations between White-Fronted Terns and Hector’s Dolphins in New Zealand. The Condor, 100: 560-562.
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Associations

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:

  • Stockin, K., R. Law, W. Roe, L. Meynier, E. Martinez, P. Duignan, P. Bridgen, B. Jones. 2010. PCBs and organochlorine pesticides in Hector’s (Cephalorhynchus hectori hectori) and Maui’s (Cephalorhynchus hectori maui) dolphins. Marine Pollution Bulletin, 60: 834-842.
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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:

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Life History and Behavior

Behavior

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

  • Thorpe, C., R. Bates, S. Dawson. 1991. Intrinsic echolocation capability of Hector’s dolphin, Cephalorhynchus hectori. Journal of the Acoustical Society of America, 90/6: 2931-2934.
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Life Expectancy

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.

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Lifespan, longevity, and ageing

Observations: Their lifespan is frequently cites as 20 years, but given the lack of detailed studies, their maximum longevity has to be classified as unknown.
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Reproduction

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

  • Brager, S. 1999. Association patterns in three populations of Hector’s dolphin, Cephalorhynchus hectori. Canadian Journal of Zoology, 77: 13-18.
  • Brager, S., S. Dawson, E. Slooten, S. Smith, G. Stone, A. Yoshinaga. 2002. Site fidelity and along-shore range in Hector’s dolphin, an endangered marine dolphin from New Zealand. Biological Conservation, 108: 281-287.
  • Dawson, S. 1991. Incidental catch of Hector’s dolphin in inshore gillnets. Marine Mammal Science, 7/3: 283-295.
  • Dawson, S., E. Slooten. 1993. Conservation of Hector’s dolphins: The case and process which led to the establishment of the Banks Peninsula Marine Mammal Sanctuary. Aquatic Conservation: Marine and Freshwater Ecosystems, 3/3: 207-221.
  • Slooten, E. 1991. Age, growth, and reproduction in Hector’s dolphins. Canadian Journal of Zoology, 69: 1689-1700.
  • Slooten, E. 1994. Behavior of Hector’s Dolphin: Classifying Behavior by Sequence Analysis. Journal of Mammalogy, 75/4: 956-964.
  • Slooten, E., S. Dawson, H. Whitehead. 1993. Associations among photographically identified Hector’s dolphins. Canadian Journal of Zoology, 71: 2311-2318.
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Conservation

Conservation Status

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

  • Slooten, E., F. Lad. 1991. Population biology and conservation of Hector’s dolphin. Canadian Journal of Zoology, 69: 1701-1707.
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IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A4d

Version
3.1

Year Assessed
2013

Assessor/s
Reeves, R.R., Dawson, S.M., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K.

Reviewer/s
Brownell Jr., R.L. & Cooke, J.

Contributor/s

Justification
This species is considered to be Endangered A4d due to an ongoing and projected decline of greater than 50% over 3 generations (approx. 39 years, Slooten et al. 2000) considering both the past and the future. It is also important to consider that although its extent of occurrence and area of occupancy likely exceed the thresholds for criteria B1, B2 and D2, Hector’s Dolphin has the most limited range of any marine cetacean other than the Vaquita (Phocoena sinus). In a population viability analysis, the estimated rate of decline was 74% over 3 generations where the time period under consideration was from 1970-2009 (Slooten 2007). The main cause of population decline is ongoing bycatch in fisheries.

History
  • 2008
    Endangered
  • 2000
    Endangered
  • 1996
    Vulnerable
  • 1996
    Vulnerable
    (Baillie and Groombridge 1996)
  • 1994
    Indeterminate
    (Groombridge 1994)
  • 1990
    Vulnerable
    (IUCN 1990)
  • 1988
    Insufficiently Known
    (IUCN Conservation Monitoring Centre 1988)
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Status

Classified as Endangered (EN- A1d, C1) by the IUCN Red List 2002 (2). Listed on Appendix II of CITES, and listed under ASCOBANS under the auspices of the Convention on Migratory Species (CMS or Bonn Convention) (1).  The North Island subpopulation is classified as Critically Endangered (CR - C1, D) (2).
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Population

Population
Studies of mitochondrial and nuclear DNA show that North Island Hector's dolphins are genetically distinct from any of the South Island subpopulations, with no overlap of maternal lineages between them (Pichler et al. 1998). Such differences over such a small geographic scale have not been observed in any other genetic studies of marine mammals (Dawson et al. 2001).

Recent surveys indicate that the South Island Hector’s dolphin populations collectively number about 7,270 individuals (CV = 15.8%) (Dawson et al. 2004; Gormley et al. 2005). The North Island subspecies is estimated to number about 111 (CV = 44%), and that population’s abundance and range appear to have been declining rapidly over the past 30 years (Slooten et al. 2006b; Dawson et al. 2001).

Population Trend
Decreasing
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Threats

Major Threats
Hector’s dolphin faces serious pressures from human activities given its limited coastal distribution. The main threat to the species in general is entanglement in gillnets (Dawson 1991; Slooten and Lad 1991; Dawson and Slooten 1993; Martien et al. 1999; Secchi 2006; Slooten 2007; DOC and Mfish 2007), with trawl fisheries also causing some mortality. Amateur gillnetting (as opposed to commercial gillnetting) is a significant part of the problem (Dawson and Slooten 2005). Sixty percent of all dead Hector’s dolphins for which cause of death could be determined, had died as a result of gillnet entanglement (DOC and Mfish 2007). Risk analyses for Hector’s and Maui’s dolphins indicate that recent levels of mortality are unsustainable (Slooten and Lad 1991; Martien et al. 1999; Slooten et al. 2000; Burkhart and Slooten 2003; Slooten 2007; DOC and Mfish 2007). This conclusion is robust to the uncertainty in abundance, mortality, and vital rates (Slooten et al. 2000; Slooten 2007). The most recent population viability analysis indicates continued population declines (Slooten 2007). Additional threats include pollution, disease, vessel traffic, and habitat modification (Stone and Yoshinaga 2000).
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This species was once hunted for bait, but this has now stopped (5). Due to the coastal habitat of Hector's dolphin, the species is vulnerable to a large number of different threats such as chemical pollution, vessel traffic and habitat modification (2). Currently the most important threat to the survival of this species is bycatch by the fishing industry, particularly entanglements in gillnets that is now reported to occur throughout the range (2).
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Management

Conservation Actions

Conservation Actions
The species is listed in CITES Appendix II.

The entire range is within New Zealand waters, and therefore national conservation measures are discussed here. The New Zealand Government has created two protected areas to promote the conservation of C. hectori, and it is thought that these areas have contributed to reduced mortality in recent years. The Banks Peninsula Marine Mammal Sanctuary was established in 1988 under the Marine Mammals Protection Act to protect Hector’s dolphins. The 1,170 km² sanctuary extends 70 nautical miles alongshore around the Banks Peninsula to the Rakaia River and out to 4 nautical miles offshore (Dawson and Slooten 2005). Its effectiveness has been compromised by the interests of sports and commercial fishermen and by the fact that the dolphins’ offshore distribution extends beyond the protected area (Dawson and Slooten 1993). At Banks Peninsula the dolphins are found further offshore than elsewhere, probably because the bathymetry there slopes more gradually. Up to 65% of the dolphins in the area occur outside the sanctuary boundaries in winter months (Slooten et al. 2006a).

The protected area established for Maui’s dolphins stretches for 210 nautical miles along the west coast of the North Island out to 4 nautical miles offshore. Although this area was closed to gillnetting under the Fisheries Act in 2003, gillnetting has continued inside the harbors, and trawling is restricted only within the first nautical mile offshore (Slooten et al. 2006b).

Discussions between the Ministry of Fisheries and Department of Conservation are currently (early 2008) underway to develop a more comprehensive management plan. A continuing high level of bycatch mortality indicates that stronger protection from entanglement in commercial and recreational fisheries is needed. Protected areas, reduced gillnet fishing effort and changes in fishing methods have been recommended as necessary to ensure the species’ long-term persistence (e.g. Martien et al. 1999, Burkhart and Slooten 2003, Slooten 2007; DOC and Mfish 2007). Meetings of stakeholders have concluded that fishery mortality must be reduced to zero to allow the North Island subspecies to recover (Dawson et al. 2001; Slooten et al. 2006a). Several other small subpopulations (100 individuals or fewer) are at a similar risk from entanglement (Burkhart and Slooten 2003; Slooten 2005). Recent surveys (Dawson et al. 2004, Slooten 2005, Slooten et al. 2006a,b) indicate that restricting gillnet fisheries to waters >100 m deep would have a major benefit in terms of reducing bycatch. In waters <100 m deep it would also be advisable to institute observer programs on any trawl fisheries that operate in Hector’s dolphin habitat.
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Conservation

The New Zealand Marine Mammals Protection Act has made the deliberate killing or injury of marine mammals illegal (2). Under this act, the New Zealand Department of Conservation has designated a 1170 km² area as a Marine Mammal Sanctuary (5), which will provide protection for the species. Bycatch, although not illegal is possible to regulate (2), and it is clear that measures must be taken to eliminate this threat if this diminutive dolphin is to survive (6).
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Relevance to Humans and Ecosystems

Benefits

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.

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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

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Risks

IUCN Red List Category

Endangered (EN)
  • IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
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Wikipedia

Hector's dolphin

Hector's dolphin (Cephalorhynchus hectori) is the best-known of the four dolphins in the genus Cephalorhynchus and is found only in New Zealand. At approximately 1.4 m in length, it is one of the smallest cetaceans, and New Zealand's only endemic cetacean.

Two subspecies occur: C. h. hectori, the more numerous subspecies, is found around the South Island, and the critically endangered Maui's dolphin (C. h. maui) is found off the northwest coast of the North Island.[2] Maui's dolphin is one of the eight most endangered groups of cetaceans. The Hector's dolphin is also the world's smallest and rarest dolphin.[3] A 2010/2011 survey by the New Zealand Department of Conservation estimated only 55 adults remained.[4]

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 found of the dolphin. The species was scientifically described by Belgian zoologist Pierre-Joseph van Beneden in 1881.

Māori names for Hector's and Maui's dolphin include tutumairekurai, tupoupou and popoto.

Physical description[edit]

Hector's dolphin has a unique rounded dorsal fin.

Hector’s dolphin is the smallest of the dolphins. 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).[5] The species is sexually dimorphic, with females being slightly longer and heavier than males. 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 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 same as adults, although the grey has a darker hue. Four to six vertical pale stripes, caused by fetal folds affecting the pigmentation, are present on the calf’s body until an age of about six months.

Population and distribution[edit]

Hector's dolphins are endemic to the coastal regions of New Zealand. The species has a fragmented distribution around the entire South Island, although only very occasional sightings occur in the deep waters of Fiordland. The largest populations live on the east and west coasts of the South Island, most notably on Banks Peninsula and Te Waewae Bay[7][8] while smaller local groups are scattered along entire South Island coasts such as at Cook Strait, Kaikoura, West Coast, Catlins (e.g. Porpoise Bay, Curio Bay), and Otago coasts (e.g.Karitane, Oamaru, Otago Harbour, Blueskin Bay).[9] Maui’s dolphin lives on the west coast of the North Island between Maunganui Bluff and Whanganui.[10] Occasionally, Hector's Dolphins can reach North Island up to Bay of Plenty or Hawke's Bay.[11]

The latest published estimate of South Island Hector's dolphins is 7,270. This is only 27% of the population estimated in 1970 which was about 30,000.[12] The latest estimate of Maui's dolphin is 55 individuals (1 year and older). Additional population surveys have been carried out off the east coast in 2012 and 2013. The results of these surveys have not yet been published in a peer-reviewed scientific journal.

The species' range includes shallow waters down to 100 m (330 ft) deep, with very few sightings in deeper waters.[13][14] The 100-m depth contour is a better predictor of offshore distribution, depending on water depth, they are found up to 20 nautical miles or more from the coast. In some areas, the seasonal difference in distribution is pronounced, with Hector's dolphins being sighted closer offshore and in shallower water in summer, and more spread out in winter. This is thought to be related to movements of their prey species. They tend to spend a lot of their time by small reef systems and surf zones of the South Island of New Zealand.[15]

As Hector's dolphins group together, they are segregated by sex the majority of the time. Because the groups are either all male or female, the problems associated with reproduction harshly increase. Due to the difficulty in finding mates in addition to the small population of the species, the population only continues to decline.[16] Studies have suggested Hector's dolphins have sex segregation becausenursing or pregnant female dolphins are at greater risk from predators. Also, male dolphins show aggression when around other females or when seeking sexual activities. Sex segregation more likely occurs as a combination of these reasons.[17]

Extreme isolation occurs in Hector's dolphins over the summer due to high site fidelity, meaning certain pods only stay in specific shore locations. This results in hindered gene flow between populations and ultimately leads to gene isolation.[18]

Ecology and life history[edit]

Data from field studies, stranded individuals, and dolphins caught in fishing nets have provided information on their life history and reproductive parameters.[5] Photo-ID research at Banks Peninsula, and other locations around the South and North Island since 1984 has shown that individuals reach around 23 years of age. Males attain sexual maturity between five and nine years of age, and females have their first calf between seven and nine years old.[5] The calving interval is two to four years.

These life-history characteristics mean that Hector’s dolphins, like many other small cetaceans, have a low potential for population growth. Maximum population growth rate has been estimated to be 1.8-4.9% per year, although the lower end of this range is probably more realistic.[19]

Foraging and predation[edit]

Hector's dolphins at Porpoise Bay, in the Catlins

Hector's dolphins live in groups of two to eight individuals. They feed at the ocean surface and sea floor, with their diets including ahuru, yellow-eyed mullet, kahawai, arrow squid, herring, and red cod.[20]

Hector’s dolphins are generalist feeders, with prey selection based on size rather than species. Typically, they feed on smaller prey which tend to measure under 10 cm. in length.[21] Stomach contents of dissected dolphins have included surface-schooling fish, midwater fish, and squid, and a wide variety of benthic species.[22] 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. Many Hector's dolphins can be observed following fishing trawlers as a result of the amount of disturbed or escaped flatfish and red cod on which the species typically feed. However, this activity can result in the unwanted bycatching of the species.[23]

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.[24]

Natural predators of Hector’s dolphins include sharks and killer whales (orca). Remains of Hector's have been found in sevengill and blue shark stomachs.[25]

Although the biggest threat to this endangered species is inshore fishing, they also suffer from an infectious agent, Toxoplasma gondii. A study of 28 captured Hector's dolphins showed seven of them died due to taxoplasmosis. These dolphins were examined, and hemorrhagic lesions in the lungs, liver, lymph nodes, and adrenals were found.[26]

Conservation[edit]

Dolphin deaths in bottom-set gillnets and trawl fisheries[27] have been responsible for substantial population declines in the last four decades. Gillnets are made from lightweight monofilament that is difficult for dolphins to detect, especially when they are distracted (e.g. chasing fish) or moving around without using echolocation. Hector's and Maui's dolphins swim into the nets, get caught, and drown - or more accurately, suffocate (breathing is active in dolphins). Hector's dolphins are actively attracted to trawling vessels and can frequently be seen following trawlers and diving down to the net. Occasional mistakes can lead to injury or death.

The nationwide estimate for bycatch in commercial gillnets is 110-150 dolphins per year[28] which is far in excess of the sustainable level of human impact.[29] Deaths in fishing nets are the most serious threat (responsible for more than 95% of the human-caused deaths in Maui's dolphins), with currently lower level threats including tourism, disease, and marine mining.[30][31]

The New Zealand government proposed a set of plans to avoid further extinction of Hector's dolphin, including protecting/closing areas where dolphins are normally found and changing fishing methods to avoid catching dolphins. The plan involves three steps; The first is to change voluntary codes involving practice and monitoring for fisherman. The second is to close inshore areas from fishing. The third plan is formed around the around the potential biological removal (PBR) concept which tells how much change would need to be done to protect the dolphins and how much of the dolphins' extinction is caused by humans. PBR testing was done in eight bodies of water surrounding the South Island of New Zealand. These test unfortunately resulted in telling the time it would take to determine the populations of dolphins in these waters is much longer than expected and cannot be done until the populations are depleted, but affirms more protection needs to occur in these waters.[32]

The first marine protected area (MPA) for Hector's dolphin was designated in 1988 at Banks Peninsula, where commercial gillnetting was effectively prohibited out to 4 nmi (7.4 km; 4.6 mi) offshore and recreational gillnetting 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 bycatch outside the MPAs.[10]

Additional protection was introduced in 2008, banning gillnetting within 4 nmi of the majority of the South Island’s east and south coasts, out to 2 nmi (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.[33] Five marine mammal sanctuaries were designated in 2008 to manage nonfishing-related threats to Hector’s and Maui’s dolphins.[34] Their regulations include restrictions on mining and seismic acoustic surveys. Further restrictions were introduced into Taranaki waters in 2012 and 2013 to protect Maui's dolphins.[35]

The Scientific Committee of the International Whaling Commission has recommended extending protection for Maui's dolphin further south to Whanganui and further offshore to 20 nmi from the coastline. The IUCN has recommended protecting Hector's and Maui's dolphins from gillnet and trawl fisheries, from the shoreline to the 100 m depth contour.

See also[edit]

References[edit]

  1. ^ Reeves, R.R., Dawson, S.M., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. (2008). "Cephalorhynchus hectori". IUCN Red List of Threatened Species. Version 2012.2. International Union for Conservation of Nature. Retrieved 18 January 2013. 
  2. ^ Baker, Alan N.; Smith, Adam N.H.; Pichler, Franz B. (2002). "Geographical variation in Hector's dolphin: recognition of a new subspecies of Cephalorhynchus hectori". Journal of the Royal Society of New Zealand 32 (4): 713–727. doi:10.1080/03014223.2002.9517717. Retrieved 18 June 2013. 
  3. ^ "Hector's Dolphin." WorldWildlife.org. World Wildlife Fund, n.d. Web. 23 Oct. 2014.
  4. ^ "Maui's dolphin abundance estimate". New Zealand Department of Conservation. Retrieved 2012-03-13. 
  5. ^ a b c Slooten, E. and Dawson, S.M. 1994. Hector’s dolphin Cephalorhynchus hectori. Pp. 311-333 in: Handbook of Marine Mammals. Volume V (Delphinidae and Phocoenidae) (S.H. Ridgway and R. Harrison eds). Academic Press. New York.
  6. ^ Slooten, E. 1991. Age, growth and reproduction in Hector’s dolphins. Canadian Journal of Zoology 69: 1689-1700.
  7. ^ Slooten, E., Dawson, S.M. and Rayment, W.J. 2004. Aerial surveys for coastal dolphins: abundance of Hector’s dolphins off the South Island West Coast, New Zealand. Marine Mammal Science 20:477-490.
  8. ^ Dawson, S.M., Slooten, E., DuFresne, S.D., Wade, P. and Clement, D.M. 2004. Small-boat surveys for coastal dolphins: Line-transect surveys of Hector’s dolphins (Cephalorhynchus hectori). Fishery Bulletin 102: 441-451.
  9. ^ Slooten L.. Benjamins S.. Turek J.. 2011. Potential impacts of Project Next Generation on Hector’s'dolphins and other marine mammals. Otago University. Retrieved on November 4, 2014
  10. ^ a b Slooten, E., Dawson, S.M., Rayment, W. and Childerhouse, S. 2006. "A new abundance estimate for Maui’s dolphin: What does it mean for managing this critically endangered species?". Biological Conservation 128: 576-581.
  11. ^ Tait M.. 2012. Creatures lurking in Bay waters. the Hawkes Bay Today. Retrieved on November 4, 2014
  12. ^ Slooten, E. 2007a: Conservation management in the face of uncertainty: effectiveness of four options for managing Hector’s dolphin bycatch. Endangered Species Research 3(2): 169–179.
  13. ^ Bräger, S., Harraway, J. and Manly, B.F.J. 2003. Habitat selection in a coastal dolphin species (Cephalorhynchus hectori). Marine Biology 143: 233-244.
  14. ^ Rayment, W., Dawson, S. and Slooten, E. In press. Seasonal changes in distribution of Hector’s dolphins at Banks Peninsula, New Zealand: implications for protected area design. Aquatic Conservation: Marine and Freshwater Ecosystems. doi:10.1002/aqc.1049.
  15. ^ Bejder, Lars, and Steve Dawson. "Abundance, Residency, and Habitat Utilisation of Hector's Dolphins () in Porpoise Bay, New Zealand." New Zealand Journal of Marine and Freshwater Research 35.2 (2001): 277-87. Web.
  16. ^ Webster, T. A., Dawson, S. M., & Slooten, E. (2009). Evidence of Sex Segregation in Hector's Dolphin (Cephalorhynchus hectori). Aquatic Mammals, 35(2), 212-219.
  17. ^ Webster, Trudi A., Stephen M. Dawson, and Elisabeth Slooten. "Evidence of Sex Segregation in Hector's Dolphin (Cephalorhynchus Hectori)." Aquatic Mammals 35.2 (2009): 212-19. Web.
  18. ^ Bräger, Stefan, Stephen M. Dawson, Elisabeth Slooten, Susan Smith, Gregory S. Stone, and Austen Yoshinaga. "Site Fidelity and Along-shore Range in Hector's Dolphin, an Endangered Marine Dolphin from New Zealand." Biological Conservation 108.3 (2002): 281-87.
  19. ^ Slooten, E. and Lad, F. 1991. Population biology and conservation of Hector’s dolphins. Canadian Journal of Zoology 69: 1701-1707.
  20. ^ Protection of Hector's dolphins around Bank's Peninsula. Department of Conservation. 1988. ISBN 0478010605. 
  21. ^ Miller, Elanor, Chris Lalas, Steve Dawson, Hiltrun Ratz, and Elisabeth Slooten. "Hector's Dolphin Diet: The Species, Sizes and Relative Importance of Prey Eaten by Cephalorhynchus Hectori, Investigated Using Stomach Content Analysis." Marine Mammal Science 29.4 (2012): 606-28. Web.
  22. ^ Jenny Riches. "Hector's and Maui's survival in Kiwi's hands, says WWF". Retrieved May 11, 2007. [dead link]
  23. ^ Rayment, William, and Trudi Webster. "Observations of Hector's Dolphins () Associating with Inshore Fishing Trawlers at Banks Peninsula, New Zealand." New Zealand Journal of Marine and Freshwater Research 43.4 (2009): 911-16. Web.
  24. ^ Kyhn, L.A.; Tougaard, J.; Jensen, F.; Wahlberg, M.; Stone, G.; Yoshinaga, A.; Beedholm, K.; Madsen, P.T. 2009: Feeding at a high pitch: source parameters of narrow band, high-frequency clicks from echolocating off-shore hourglass dolphins and coastal Hector’s dolphins. Journal of the Acoustical Society of America 125(3): 1783–1791.
  25. ^ Banks Peninsula Marine Mammal Sanctuary Technical Report. Department of Conservation. 1992. pp. B–9. ISBN 0-478-01404-X. 
  26. ^ Roe, W.d., L. Howe, E.j. Baker, L. Burrows, and S.a. Hunter. "An Atypical Genotype of Toxoplasma Gondii as a Cause of Mortality in Hector's Dolphins (Cephalorhynchus Hectori)." Veterinary Parasitology 192.1-3 (2013): 67-74. Web.
  27. ^ Starr, P. and Langley, A. 2000. Inshore Fishery Observer Programme for Hector’s dolphins in Pegasus Bay, Canterbury Bight, 1997/1998. Published client report on contract 3020, funded by Conservation Services Levy. Department of Conservation, Wellington. 28p.
  28. ^ Davies, N., Bian, R., Starr, P., Lallemand, P., Gilbert, D. and McKenzie, J. (2008). Risk analysis of Maui’s dolphin and Hector’s dolphin subpopulations to commercial setnet fishing using a temporal-spatial age-structured model. Ministry of Fisheries, Wellington, New Zealand. Retrieved February 2013. 
  29. ^ Slooten, E. and Dawson, S.M. 2008. Sustainable levels of human impact for Hector’s dolphin. The Open Conservation Biology Journal 2: 37-43.
  30. ^ Bejder, L., Dawson, S.M. and Harraway, J.A. 1999. Responses by Hector's dolphins to boats and swimmers in Porpoise Bay, New Zealand. Marine Mammal Science 15: 738-750.
  31. ^ Stone, G. S. and Yoshinaga, A. 2000. Hector's dolphin (Cephalorhynchus hectori) calf mortalities may indicate new risks from boat traffic and habituation. Pacific Conservation Biology 6: 162-170.
  32. ^ Slooten, E., and S.M. Dawson. "Sustainable Levels of Human Impact for Hector's Dolphin." The Open Conservation Biology Journal 2 (2008): 37-43. Web.
  33. ^ "Hector's Dolphins". Ministry of Fisheries. 2008-10-01. Retrieved 2010-02-16. 
  34. ^ "Marine mammal sanctuaries: Marine protected areas". Department of Conservation. Retrieved 2010-02-16. 
  35. ^ Smith, Nick; Guy, Nathan. "Additional protections and survey results good news for dolphins". beehive.govt.nz. New Zealand Government. 

Further reading[edit]

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