Cephalorhynchus hectori (P.-J.
van Beneden, 1881)
English: Hector's dolphin
Spanish: Delfín de Héctor
French: Dauphin d'Hector
Hector's Dolphin © Wurtz-Artescienza (see links).
Similar to the other representatives of the genus, these are small,
blunt-headed chunky dolphins without a beak (and therefore often
wrongly called porpoises) with rounded, almost paddle-shaped flippers.
The dorsal fin is proportionally large and with a rounded, convex
trailing edge, like a "Mickey Mouse ear". The colour scheme
of the Hector's dolphin is well defined with areas of grey, black
and white. Mass and size of the two subspecies found in New Zealand
vary: North Island 152 cm, 65 kg, South Island 145 cm, 50 kg (Dawson,
The sides of the head, the flippers, dorsal fin and the tail are
all gray to black. The belly is white except for a small area between
the flippers. There is also a distinctive finger-like swoosh of
white that extends from the belly, along the flanks towards the
tail. (Jefferson et al. 2008).
Hector's dolphin is endemic to inshore waters of the main islands
of New Zealand. Pichler et al. (1998) used mitochondrial DNA analysis
to determine that C. hectori was subdivided into sub-populations,
which total four (Pichler, 2002): North Island, East Coast South
Island, West Coast South Island, and South Coast South Island -
with only little or no female dispersal. The North Island subpopulation
of Hector's Dolphin was subsequently recognized as a subspecies,
C. h. maui (Baker et al. 2002).
Distribution of Cephalorhynchus hectori (Reeves
et al. 2008): coastal waters of New Zealand,
especially South Island and the western coast of North Island (©
here for large map).
Cephalorhynchus hectori hectori: most common
along the east and west coasts of South Island between 41° 30'
and 44° 30'S, with hot spots of abundance at Banks Peninsula
and between Karamea and Makawhio Point. An apparently isolated population
exists in Te Wae Wae Bay, on the Southland coast (Dawson, 2009).
Cephalorhynchus hectori maui: occurs on the
west coast of North Island between 36°25' and 39°'S, but
is generally only seen between the entrance of Manuaku Harbour and
Port Waikato (Dawson, 2009).
3. Population size
North Island: Slooten et al. (2006a) from 2004 data, estimated
the total C. h. maui population size at 111 individuals (95%
confidence interval = 48-252). The small population size confirms
its critically endangered IUCN status and the suggestion that it
is vulnerable to extinction (Dawson et al. 2001). It has been suggested
that one dolphin every 6.4 years is the maximum level of human-caused
mortality to maintain the population, therefore, considerable steps
need to be taken to allow for population recover.
South Island: Line-transect surveys of Hector's dolphins
on the East Coast of the South Island conducted prior to 2000 in
the coastal zone to 4 nm offshore yielded an abundance estimate
of 1,880 individuals (CV=15.7%) (Dawson et al. 2004). Maximum densities
peaked at 5-18 individuals per nautical mile of coastline between
Cape Foulwind and Hokitika (Braeger and Schneider 1998).
Aerial surveys prior to 2002 suggested that the populations of C.
h. hectori numbered ca. 1,900 (east coast) and ca. 5,400 (west
coast) animals (Slooten et al 2002). In 2000 - 2001 the total population
estimate for South Island Hector's dolphins was 7,270 (CV = 16.2%)(Slooten
et al. 2002; 2004). The most recent estimate was 7,873 (Slooten,
2007), showing little change for the past 7 years.
4. Biology and Behaviour
Habitat: The most consistent factor influencing the distribution
of Hector's dolphins appears to be their preference for shallow
waters. This may explain their apparent absence from Fiordland,
where depths in excess of 300 m are very common, and their apparent
reluctance to cross Cook Strait to North Island waters. Hector's
dolphins inhabit a wide range of water temperatures (surface temperature
6.3-22°C;) and water turbidity (<10cm to >15m) (Slooten
and Dawson, 1994).
Bräger et al. (2003) encountered most dolphins in waters <
39 m depth, with < 4 m Secchi disk visibility and > 14 °C
temperature. Habitat selection by dolphins differed between study
areas, particularly between east and west coasts, in summer (December-February)
and winter (June-August). Dolphin abundance appeared to change seasonally
in some study areas. This was so especially in summer (the main
reproductive season), when dolphins (frequently with calves) occupied
shallow and turbid waters, whereas in winter less use was made of
this habitat, possibly due to a more offshore distribution of their
Behaviour: Large groups often show eyecatching behaviour
such as leaps, chases and lobtailing. Hector's dolphins are strongly
attracted to boats and readily bow-ride (Dawson, 2009). Mothers
with newborn calves are shy and seldom approach stationary or moving
boats. Except in ports and other areas of very intensive boat traffic,
it seems unlikely that the presence of boats will greatly affect
the behaviour and distribution of this species (Slooten and Dawson,
1994, and refs. therein).
Schooling: Hector's dolphins live in groups of 2 to 8 individuals.
Larger aggregations of up to 50 can be seen at times (Jefferson
et al. 1993). Braeger and Schneider (1998) reported that small to
medium-sized groups of Hector's dolphins with 1-60 individuals were
observed in almost all areas of the west coast of South Island in
winter as well as in summer. Groups rarely stay in tight formation,
though several individuals may swim and surface together in a row.
Most active when small groups join together (Carwardine, 1995).
Reproduction: Females bear their first calf at age 6-9 years,
and males reach sexual maturity at 5-9 years. Mating and calving
occur in spring to late summer and gestation lasts 10-11 months.
Females calve every 2-4 years. At Banks peninsula, six photographically
identified Hector's dolphins attained a maximum age of at least
22 years(Dawson, 2009).
Food: Hector's dolphins appear to feed mostly in small groups.
The dolphins feed opportunistically, both at the bottom and throughout
the water column, and take a wide variety of species. Surface-schooling
fish (e.g. yellow-eyed mullet, Aldrichetta forsteri, kahawai,
Arripis trutta) and arrow squid, Nototadarus sp.,
are taken along with benthic fishes such as ahuru, Auchenoceros
punctatus, red cod, Pseudophycis bacchus and stargazer,
Crapatalus novaezelandiae. Crustaceans are occasionally found
among the stomach contents, including Ovalipes catharus,
Hymenosoma depressum and Macroptkalmus hirtipes, but
these appear to be from the stomach contents of fish taken by the
Hector's dolphins. In summer, dolphins occasionally follow inshore
trawlers, apparently stationing themselves behind the cod-end of
the net. The dolphins themselves are rarely caught in trawl nets
(Slooten and Dawson, 1994, and refs. therein).
Despite wide-ranging surveys over more than 20 years, no sightings
of the same Hector's dolphin were more than 106 km apart (Dawson,
2009). Most individuals ranged over less than 60 km (Mean 31.0 km,
SE = 2.43) of coastline. Site fidelity was high: e.g. in Akaroa
Harbour individuals were seen for about two thirds of the years
they were known to be alive (Bräger et al. 2002).
Stone et al. (1998) confirmed short-range movement patterns via
radio-telemetry and found them to be remarkably consistent. Dolphins
remained in Akaroa Harbor for a period of between one and five hours,
after which they left in a westerly direction, always in the late
afternoon or early evening. Two dolphins returned to Akaroa Harbor
the next morning. These patterns support previous studies which
described a diurnal movement pattern for this species (Stone et
A similar picture was obtained from a theodolite tracking and boat-based
photo-identification survey in Porpoise Bay, on the south-east corner
of South Island. Results are consistent with the model of a small
resident population (48 dolphins; 95% CI = 44-55 in 1996/97) that
is visited occasionally by members of neighbouring populations.
Dolphins spent a large proportion of their time in a small area
inside the bay. There, no pattern of diurnal movement into and out
of the bay was observed (Bejder and Dawson, 2001).
Direct catch: Hector's and Maui's dolphins are protected
under the Marine Mammals Protection Act (1978) therefore any direct
take is illegal.
Incidental catch: Total population size today (7,873) was
estimated at 27% of the population size estimated for 1970 (29,316,
CV 0.16), before a major expansion of commercial gillnetting (Slooten,
2007).The catch of Hector's dolphins in coastal gillnets, many of
them used by recreational fishermen, has been repeatedly documented.
It is believed that the effects of fishing are the greatest cause
of human induced mortality on the dolphins (MoFNZ 2007).One example
is that strandings are exclusively of single animals and many beach-cast
dolphins bear cuts and abrasions consistent with being caught and
killed in gill nets (Slooten and Dawson, 1994). Due to evidence
that the catches were seriously threatening the population, the
N.Z. government created a marine mammal sanctuary in 1989 to protect
them (Jefferson et al. 1993; Slooten and Dawson, 1994).
Stone et al. (1997) showed that Hector's dolphin distributions
were affected by 10 kHz pingers and that dolphins avoided the immediate
area where the pingers were active. This suggests that pinger use
could reduce mortality in gill nets. A pilot study to test the use
of electronic monitoring (EM) systems to examine interactions between
protected species and fishing gear (McEldeny et al. 2007) such as
inshore set net and trawl fisheries was shown to effectively monitor
retrieval operations and encounters with protected and endangered
Clearly, these efforts are promising: Reducing fisheries mortality
to levels approaching zero shows the strongest promise of meeting
national and international guidelines for managing dolphin bycatch,
with a 59% probability of reaching 50% of estimated 1970 population
size by 2050 (Slooten, 2007).
Slooten et al. (2006b) suggested a size extension of the Banks
Marine Sanctuary beyond the 4 nm from shore: In summer, the proportion
of sightings inside the 4-nautical-mile offshore boundary of the
sanctuary was 79%. This dropped to just over 35% in winter. The
authors suggest that appropriate modifications to the sanctuaries
extension could significantly reduce mortality due to bycatch. Since
then, alterations to the Banks Peninsula marine mammal sanctuary
have been notified, extending the northern and southern boundaries
significantly while at the same time extending the seaward boundary
to 12 nautical miles. Furthermore, a series of additional marine
mammal sanctuaries have been put in place (Dept. Cons. NZ, 2010).
Pollution: The strictly coastal distribution of this species
makes it vulnerable to accumulation of pollutants such as heavy
metals and pesticide residues. Although their precise biological
effects are poorly known, the level of some of the contaminants
gives some cause for concern. Moderate to high levels of DDT, PCBs
and Dioxin have been found in the tissues of Hector's dolphins.
These compounds are known to interfere with reproduction and their
effects are worsened by synergism between compounds. Mercury, cadmium
and copper levels are also relatively high when compared to other
species. It is not known to what extent pesticide contamination
or other forms of pollution contribute to mortality or to the low
reproductive rates observed in Hector's dolphins (Slooten and Dawson,
Tourism: There has been a rapid growth in marine mammal-based
tourism around the world, because marine mammals have a wide appeal
for many people and are readily found around many coastal areas
and are therefore readily accessible. Marine mammal-based tourism
in New Zealand is a wide-ranging, species-diverse industry with
an increasing demand for permits from land, boat and air-based platforms.
One publication cites that e.g. a total of 74 permits at 26 sites
have been issued from Maunganui to Stewart Island (Constantine,
Hector's Dolphins are not displaced by boats or by human swimmers.
Swimmers cause only weak, non-significant effects, perhaps because
the dolphins can very easily avoid them. Reactions to dolphin-watching
boats are stronger. Analyses of relative orientation indicate that
dolphins tend to approach a vessel in the initial stages of an encounter
but become less interested as the encounter progresses. (Bejder
et al. 1999).
The endemic New Zealand Hector's dolphin is considered one of the
rarest species of marine dolphin (WWF, 2009).
The North island population of C. h. maui is considered "Critically
Endangered" by the IUCN (Reeves et al. 2008): it is assumed
that there are fewer than 250 mature animals, and the principal
cause for the population decline has not been stopped; gillnetting
and trawling continue in areas occupied by the subspecies, with
bycatch rates exceeding recovery rate. Its vulnerability is further
increased by its fidelity to local natal ranges and the genetic
isolation of regional populations. Given its small size, reproductive
isolation and reduced genetic diversity, the North Island population
is likely to become extinct. The time-series of reduction in genetic
variation provides independent evidence of the severity of population
decline and habitat contraction resulting from fisheries and perhaps
other human activities (Pichler and Baker, 2000).
The South Island population of C. h. maui is listed as "Endangered"
by the IUCN (Reeves et al. 2008): the decline due to fisheries bycatch
seems to be ongoing (but see above) and projected to be larger than
50% over 3 generations. Furthermore, the range of the species is
New Zealand Hector's dolphin is not included in Appendix II of the
CMS because it is endemic to New Zealand.
Both subspecies are listed in CITES Appendix II.
Acknowledgement: We are grateful to Laura Boren, New Zealand
Dept. of Conservation, for kindly reviewing this species summary.
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© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.