Though Cephalorhynchus heavisidii is not typically vulnerable to predation, humans pose a potential threat due to by-catch. In general, dolphins are subject to retaliatory killings by local fisherman and are sometimes slaughtered for their meat, which is considered a delicacy in Japan. However, the biggest threat to dolphins seems to be accidental killing. Drift fishing nets catch everything in their paths, including dolphins, and prevent them from reaching the surface for air. It has been estimated that drift fishing nets have killed more than 30 million dolphins worldwide since the 1960's.
Known Predators:
Adult Heaviside’s dolphins typically weigh between 60 and 70 kg, with an average body length of 1.74 m. Maximum girth is roughly 67% of the length of the body. Each individual has between 48 and 70 teeth. They are distinguished from other dolphins by their blunt head, robust body, triangular dorsal fin, and rounded paddle-like flippers. Heaviside's dolphins have a dark gray anterior surface with a dark blue-black patch beginning midway between the dorsal fin and the snout, and extending about halfway down the ventral surface of the body. White markings on their underside form a three-pronged fork, with another white rhomboidal patch on the chest and two smaller diamond-like patches just posterior to the flippers. They also have a dark blue-black stripe, which extends from the blowhole to the cape. Sexual dimorphism has not been reported in this species.
Range mass: 60 to 75 kg.
Average length: 1.74 m.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
There is no information available regarding the average lifespan of Cephalorhynchus heavisidii in captivity or in the wild. The average lifespan of most wild delphinids ranges from 17 to 25 years, with a few living into their early 50s. Although similar averages are found for captive dolphins, few captive individuals live past their 20s. In general, delphinids are vulnerable to bacterial, fungal, and viral infections and have been found to suffer from heart and respiratory disease, stomach ulcers, and even cancer. Dolphins are also vulnerable to a number of different parasites including flukes, tapeworms, and roundworm.
Cephalorhynchus heavisidii is found exclusively in the Atlantic Ocean. Although it is most often found in waters less than 100 m deep, it has been sighted at depths up to 180 m. It is usually found in waters that are between 9 and 15ºC, but has been found in waters as warm as 19ºC. More than 87% of sightings occur in the Benguela Current.
Range depth: 180 (high) m.
Average depth: 100 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: pelagic ; coastal
Cephalorhynchus heavisidii is found in coastal waters off of Africa’s Southwestern coast, from central Angola to the southern-most tip of South Africa. This species usually remain within 8 to 10 km of the shoreline, but has been sighted up to 45 nautical miles from the coast. While some studies suggest that Cephalorhynchus heavisidii does not migrate significant distances, and that there are resident dolphins in some areas, this is not well established. One study tracked a juvenile male that swam 158 km north of where he was tagged. Another juvenile male traveled 137 km north of his tagging site over a 17 month period, suggesting that average daily movements might be small. This species appears to have low population densities of around 5 individuals per 160 km.
Biogeographic Regions: ethiopian (Native )
This species is sometimes referred to as Haviside's dolphin, rather than the more common Heaviside's dolphin.
Heaviside’s dolphins communicate visually, as dolphins have exceptional underwater vision. They also use tactile communication, swimming near other individuals and rubbing against one another to build affiliative relationships. Acoustically, they are able to communicate through a series of whistles and clicks ranging between 1.5 and 11.0 KHz. They communicate chemically by releasing pheromones from pores in their anal glands. Heaviside’s dolphins also rely heavily on echolocation to perceive their surroundings.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; acoustic ; echolocation ; chemical
Cephalorhynchus heavisidii is listed as “data deficient” on the IUCN Red List of Threatened Species. CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora) lists Cephalorhynchus heavisidii under Appendix II, meaning that though this species is not necessarily threatened with extinction, its trade must be regulated so that its survival is not jeopardized. Cephalorhynchus heavisidii is vulnerable to harpoons and guns used by humans hunting close to shore, where about 100 are killed annually. Also, entanglement in fishing gear poses a significant threat. In 1983, 67 were caught in nets off Namibia, and 57 off of South Africa. Although overfishing of their primary prey may pose a threat to their survival, little evidence exists to support this claim. As an inshore species, C. heavisidii is susceptible to pollution and boat traffic, and low levels of DDT have been found in some individuals. This species is currently protected from commercial hunting and fishing throughout its geographic range. It is also protected by a 322 km Exclusive Fishery Zone (EFZ) off the coast of South Africa and a 20 km EFZ off the coast of Namibia.
CITES: appendix ii
IUCN Red List of Threatened Species: data deficient
There are no known adverse effects of Cephalorhynchus heavisidii on humans. Although local fisherman may contend that this species decreases local fish abundance, there is no documented evidence to support this.
Cephalorhynchus heavisidii provides no known economic benefits to humans.
Cephalorhynchus heavisidii preys upon a number of different fish and cephalopods. Although this species is not a major prey item of any particular organism, body parts of dolphins have been found in the gut contents of killer whales and sharks. There is no information available regarding parasites of Cephalorhynchus heavisidii, nor has it been recorded to take part in any mutualistic or commensalistic relationships with other organisms.
The primary prey of Cephalorhynchus heavisidii includes hake and kingclip, which comprises nearly 49% of their diet. Octopods is also an important prey item for C. heavisidii, which makes up about 22% of their diet. The remainder of their diet generally consists of kingfish, gobies, and squid. Dolphins have fusiform, or torpedo shaped bodies, which allows them to swim at high speeds to avoid predation and catch prey.
Animal Foods: fish; mollusks
Primary Diet: carnivore (Piscivore )
There is no information available regarding the mating system of Heaviside's dolphins. However, bottlenose dolphins, spinner dolphins, and common dolphins are promiscuous.
Heaviside's dolphins breed once every 2 to 4 years from spring to late summer. Gestation lasts for 10 to 11 months. Females usually give birth to only one offspring at a time, as there is limited space for in utero development. To account for the limited space in the uterus, during development, the tail flukes and dorsal fins of fetuses are cartilaginous and fold over. Newborns average 85 cm in length. Birth mass has not been recorded for this species. However, newborn bottlenose dolphins range from 11.3 to 18.1 kg, and Irrawaddy dolphins, which average 96 cm in length at birth, has an average birth mass of 12.3 kg. There is no information available regarding weaning and time to independence for this species. Bottlenose dolphins begin weaning as early as 32 months and are fully weaned by 48 months, while time to independence ranges between 3 and 6 years. Female Heaviside's dolphins reach sexual maturity between 5 and 9 years of age, and males reach sexual maturity between 6 and 9 years of age.
Breeding interval: Haviside's dolphins breed every 2 to 4 years.
Breeding season: Haviside's dolphins breed from spring to late summer.
Range gestation period: 10 to 11 months.
Range age at sexual or reproductive maturity (female): 5 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
Cephalorhynchus heavisidii calves swim in echelon position, that is, in close proximity to the mid-lateral flank near the dorsal fin of the mother. This allows the calf extra speed at a lower tailbeat frequency, because it is able to ride along the pressure wave that its mother’s body creates. However, it has been shown that this causes extra strain on the mother, who is able to swim at only 76% of her mean maximum speed when swimming by her self. Most dolphin calves develop strong social bonds with their mother, which remains even at 3 years of age. This extended mother-young association is thought to be due largely to the still-improving physical performance and social skills of calves. There is no information available regarding paternal investment in calf development.
Parental Investment: precocial ; female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); extended period of juvenile learning
Heaviside dolphins (Cephalorhynchus heavisidii)were originally named ‘haviside’ dolphins after Captain Haviside who brought a specimen of the cetacean from the coast of Namibia to the UK in the early 19thcentury.An accidental typo resulted in the cetacean being called a ‘heaviside dolphin’ and the name stuck!
Heaviside dolphins are small and robust.They are roughly the size of an average human.An adult Heaviside dolphin is approximately1.7meters in length and weighs an average of 60 – 70 kgs.They do not have beaks so they are often mistaken for porpoises.
Heaviside dolphins are often seen in small groups of2 – 10 animals.They are shyer than their cetacean cousins but they do occasional bow ride nearby boats.They diet comprises of a variety of prey items found along their coastal habitat that stretches from along the coast of southern Angola to the southern tip of South Africa.Hake and kingklip make upto 50%of its diet. Octopods make up 25% and the remainder comprises of a mix of smaller fish.
There is no data available on the reproductive behaviour of Heaviside dolphins.There is also no data available on longevity.No wonder theIUCN Red listclassifies Heaviside dolphins as a data deficient species.However, threats have been identified for this species.These animals are prone to entanglement in a variety of inshore fishing gear (e.g., beach seines, purse seines, trawls, and gillnets).
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Heaviside's dolphin (Cephalorhynchus heavisidii)[3] is one of four dolphins in the genus Cephalorhynchus. The small cetacean is endemic to the Benguela ecosystem along the southwest coast of Africa.[4][5]
Early in the 19th century, a specimen was caught off the Cape of Good Hope and brought to the United Kingdom by a Captain Haviside of the British East India Company. Zoologist John Edward Gray, who described the species in his Spicilegia Zoologica,[3] misidentified Haviside as the surgeon John Heaviside, whom was known for his own biological collections at the time.[6] "Heaviside's Dolphin" is the recognised common name, though amongst others, "Haviside's dolphin" and "Benguela dolphin" are also used, the latter especially in Namibia.
The genus name "Cephalorhynchus" comes from the Greek kephale for ‘head’ and rhynchos for ‘beak’. For the species name "heavisidii" see the above description.
The three other species in the genus Cephalorhynchus are the Chilean dolphin (C. eutropia), the Commerson's dolphin (C. commersonii) and the Hector's dolphin (C. hectori). All are located in cool temperate shelf waters in the Southern Hemisphere.[7]
Genetic studies suggest that the Cephalorhynchus dolphins originated from a single common ancestor in Southern Africa, from which Heaviside's dolphin are the basal species.[8] Radiation around the southern hemisphere following the Antarctic Circumpolar Current (otherwise known as the West Wind Drift), first to New Zealand and then to South America, is thought to have led to the subsequent speciation within the genus.[8]
Heaviside's are small and stocky with adults reaching a maximum length and weight of 1.7m and 75 kg respectively.[9] The dolphin has a distinct black, grey and white body pattern, and is not easily confused with any other species in its range.[4] The head is cone shaped with a blunt beak. The dorsal fin is triangular in shape and centred in the middle of the back. The head and thorax are coloured light grey with darker patches around the eye. The dorsal fin, fluke and dorsal cape are a dark grey to almost black with a band that extends forward from the dorsal fin to the blowhole. The underbelly is white, with bands that extend onto the lower rear of the body. Small white patches are located just behind the pectoral fins and a single white patch extends between these fins on the chest. Sexual dimorphism is minimal, however variation in the shape of the white patch covering the genital slit is distinct between genders. In males, the patch ends in a point, but in females widens out to cover the mammary slits.[4]
Information on reproduction is limited for Heaviside's dolphins, however they are thought to be comparable to Hector's and Commerson's dolphins.[7] Females and males reach sexual maturity approximately between 5–9 years. Mating is thought to occur year-round, however individual females may only produce calves every 2–4 years. Gestation time is unknown. Maximum known lifespan is based on the oldest recorded individual at 26 years old.[6]
Typically occurs in small groups of 2–3, but numbers of 1-10 are frequent and large aggregations of ~100 individuals or more are known to form in high density areas.[6] Nursery groups (exclusively females and calves) are not formed in this species.[10]
Levels of predation are unknown, however killer whales (Orcinus orca) are known predators and there is evidence of shark attack from body scars.[11]
The species is strongly associated with the cool waters of the Benguela Ecosystem. Although the southern limit of the range is defined as Cape Point, the real southern limit beyond which sightings are extremely rare is Hout Bay, some 40 km to the north (a considerable distance for a species which shows very high site fidelity to quite small spatial scales when nearshore). The species occurs more or less continuously for 2,500 km to the north of this along the South African coast, through Namibia and into southern Angola where the northern boundary for the species remains poorly defined. Several dolphins have been sighted or accidentally caught by fishing vessels north of the Angola-Namibia border,[12][13][14][15] but no sightings were reported during a series of coastal scientific surveys at Tombua which is approximately 170 km into Angola but well south of the defined northern boundary of the Benguela Ecosystem. The northern boundary of the Benguela current shifts north and south seasonally and as Heaviside's dolphins appear closely linked to its cool waters, their northern range limit may shift along with water conditions.[4][5] Systematic surveys have dedicated effort to describing the distribution in southern South Africa[10] and current research efforts focus on local populations in Walvis Bay and Lüderitz, Namibia.[16] These locations are also popular hotspots for watching these dolphins in addition to Table Bay (Cape Town) and Britannia Bay, South Africa. Sightings are common from land and there are several dolphin watching tour companies by which Heaviside's dolphins can be seen by boat.
Recent genetic research has demonstrated evidence of population structure across the range, indicating two metapopulations (north and south) with limited genetic exchange.[17] This pattern of fragmentation is a common feature amongst the other three species in the genus Cephalorhynchus and most prevalent in the Hector's dolphin, which displays genetic isolation over very short distances.[18]
Heaviside's dolphins typically remain nearshore in the mornings where they typically socialise and rest. When nearshore their distribution patterns are remarkably predictable within and between years, with the animals showing highly consistent use of aggregation sites at the exposed western tips of most bays throughout South Africa and Namibia, but they are rarely seen in the protected shallows of these bays. Outside of bays, they show relatively high densities along exposed sandy beaches, but these may be a secondary choice after a preference for areas where there is a high abundance of their main prey item; juvenile hake (Merluccius capensis) in adjacent offshore waters. Most commonly sighted within sea surface temperatures of 9 to 15 °C (48 to 59 °F) and depths less than 100 metres (330 ft).[14]
Heaviside's dolphins are energetic and social animals, especially when nearshore in the mornings Behaviour when offshore tends to be less playful an may include a rest phase when moving offshore to feed. They are attracted to boats and frequently bow-ride.[19] Individuals can also be seen surfing in coastal waves. Iconic vertical leaps clear the water before re-entering headfirst with almost no splash.[6] Heaviside's dolphins use echolocation to find and capture prey.[20] Mating typically occurs in social groups of 3-7 individuals which remain in a small area exhibiting extensive rolling, touching and position changes with frequent leaps by one of pairs of animals which potentially serve a competitive function.
Prey items consist of mostly demersal fish and cephalopod species, predominantly juvenile hake (Merluccius capensis) and octopus, however pelagic species such as juvenile goby (Sufflogobius bibarbatus) and horse mackerel (Trachurus trachurus capensis) are also consumed especially in Namibia.[21] Foraging occurs mostly at the seabed, in shallow depths. Feeding nearshore is rarely observed.
A diurnal movement pattern is present in South Africa, whereby the dolphins move offshore in the afternoon to feed on prey rising vertically to the surface at night.[22] Movement inshore to rest and socialise occurs in the morning.[19] However, the pattern is different in Luderitz and Walvis Bay, Namibia where the movement is less pronounced and dolphins appear to stay inshore during the night, which is likely associated with foraging on different prey.[23]
Heaviside's have small home ranges of 50–80 km as measured using satellite telemetry over 2–3 months and photographic resightings over up to 3 years.[24] Some individuals have been resighted at the same location for up to 10 years.[24][25]
There has been limited research into Heaviside's diving behaviour, however a study of two dolphins fitted with satellite tags was undertaken in South Africa in 1997.[26] The maximum dive depth recorded was 147 meters, however the majority of dives were less than 50 meters.[26] Dive duration were predominantly less than 2 minutes with most dives between 0 and 1 minutes (Davis et al. 2014).[26]
Whilst typically found further from shore, dusky dolphins (Lagenorhynchus obscurus) are found throughout the range and occasionally both dolphin species are sighted in mixed groups.[10] Where both species overlap in prey selection, Heaviside's take larger prey items, potentially because they are outcompeted by the larger dusky dolphins for their preferred, smaller sized prey.[27] In central Namibia (especially Walvis Bay) Heaviside's dolphins overlap with a small populations of fewer than 100 common bottlenose dolphins REF. The bottlenose dolphin population use only water less than 15m depth while in this area Heaviside's dolphins are almost always encounteres in water deeper than 20m, suggesting some form of competitive exclusion.
As is the case with all species in the genus, Heaviside's dolphins produce narrow-band high-frequency (NBHF) echolocation clicks (centred around 125–130 kHz), and do not whistle.[28] This adaptation is theorised to allow acoustic crypsis from eavesdropping predators, as the sounds produced are outside of the detectable frequencies of killer whales.[29] Although NBHF clicks are limited in acoustic range, they have a better resolution for small targets and are thought to provide a foraging advantage in the often cluttered, nearshore environment in which these species occur.[30] Heaviside's also produce a second click type, of lower frequency and broader bandwidth, that is within the hearing range of killer whales.[31] These calls are produced most frequently in groups engaging in social behaviour. It is likely that the dolphins use these calls when socialising away from predator threat and switch to high frequency clicks when foraging and travelling.[32]
No total abundance estimate currently exists, however a population estimate of 6,345 for the region between Table Bay and Lamberts Bay, South Africa represents the southernmost populations in the species range.[19] Local population estimates for Walvis bay and Lüderitz are 508 and 494 respectively.[5] A visual and acoustic line-transect ship survey estimated an average of 1594 dolphins in the Namibian Islands’ Marine Protected Area (NIMPA) which spans 400 km of coastline along southern Namibia (REF Martin et al. 2020). Quantification of abundance throughout the range is still required.
Heaviside's dolphins are exposed to a variety of threats given their limited range in coastal shallow waters which are subject to a range of anthropogenic activities. Directed catch has occurred historically, with meat being used for human consumption.[33]
Heaviside's dolphins are exposed to several poorly quantified and rapidly changing human threats including fisheries bycatch related mortality and illegal directed catch (Elwen and Gopal, 2018; Alfaro-Shigueto et al., 2019). Recently developed mid water trawls for horse mackerel (Trachurus capensis) are considered an emerging threat.[5]
Heaviside's dolphins are listed amongst the cetacean species most vulnerable to climate change [34] as they are limited to a distribution range that includes both suitable shelf habitat and cool water temperatures (Best, 2007). The Benguela Current is the only eastern-boundary current bordered by warm-water currents at both its northern and southern limits. Consequently, small increases in water temperature could result in all shelf waters in this area becoming too warm for both species, and populations are expected to decline rather than shift poleward due to a lack of shelf habitat.
Heaviside's dolphins may be exposed to increase in the marine eco-tourism business in Namibia, which has grown without regulation in Walvis Bay (Leeney, 2014). Negative effects have been demonstrated for other coastal cetacean species, for example the impact of tour boats on bottlenose dolphin behaviour in Walvis Bay includes a reduction in resting behaviour and an increase in socialising behaviour in the presence of tour boats (indurkyhua). One Heaviside's dolphin was documented in 2010 with evidence of a propeller strike along its flank. As individuals have small home ranges they may be vulnerable to localised threats.
Prior to 2018, the International Union for Conservation of Nature (IUCN) listed the Heaviside's as ‘Data Deficient’ however, as of 2017 the status was changed to ‘Near Threatened’,[1] owing to improved knowledge on the species from multiple studies. Despite this, the overall population trend remains unknown,[5] and there are many aspects of the species biology that remain to be studied
Heaviside's dolphin is listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals[35] and is included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia. The Memorandum of Understanding was established in 2008 and aims to protect these species at a national, regional and global level.
{{cite web}}: CS1 maint: url-status (link) Heaviside's dolphin (Cephalorhynchus heavisidii) is one of four dolphins in the genus Cephalorhynchus. The small cetacean is endemic to the Benguela ecosystem along the southwest coast of Africa.
