Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Cladus: Synapsida
Cladus: Eupelycosauria
Cladus: Sphenacodontia
Cladus: Sphenacodontoidea
Cladus: Therapsida
Cladus: Theriodontia
Cladus: Cynodontia
Cladus: Mammaliaformes
Classis: Mammalia
Subclassis: Trechnotheria
Infraclassis: Zatheria
Supercohort: Theria
Cohort: Eutheria
Cohort: Placentalia
Cladus: Boreoeutheria
Superordo: Laurasiatheria
Ordo: Artiodactyla
Subordo: Whippomorpha
Infraordo: Cetacea
Cladus: Neoceti
Parvordo: Odontoceti
Cladus: Delphinida
Superfamilia: Delphinoidea
Familia: Delphinidae
Genus: Cephalorhynchus
Species: Cephalorhynchus heavisidii
Name
Cephalorhynchus heavisidii J. E. Gray, 1828
References
Cephalorhynchus heavisidii - Taxonomy
Vernacular names
Deutsch: Heaviside-Delfin
English: Heaviside's Dolphin
suomi: Benguelandelfiini
magyar: Benguela-delfin, Heaviside-delfin
日本語: コシャチイルカ
português: Golfinho-de-heaviside
svenska: Bengueladelfin
ไทย: โลมาฮาวี่ไซด์
Türkçe: Benguela yunusu
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]
Taxonomy and evolution
The Heaviside's dolphin has 14 levels of taxonomy; including a subphylum, subclass and infraclass, superorder, suborder, infraorder, and a parvorder.[6]
Nomenclature
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.[7] "Heaviside's Dolphin" is the recognised common name, though amongst others, "Haviside's dolphin" and "Benguela dolphin" are also used.
The generic name "Cephalorhynchus" comes from the Greek kephale for ‘head’ and rhynchos for ‘beak’. For the species name "heavisidii" see the above description.
Closely related species and genetic origin
The three other species in the genus Cephalorhynchus are the Hector's dolphin (C. hectori), the Chilean dolphin (C. eutropia), and the Commerson's dolphin (C. commersonii). All are located in cool temperate waters in the Southern Hemisphere.[8]
Genetic studies suggest that the Cephalorhynchus dolphins originated from a single common ancestor in South Africa, from which Heaviside's is the basal species.[9] 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, led to the subsequent speciation within the genus.[9]
Description
Morphology
Heaviside's dolphins off Walvis Bay, Namibia
Heaviside's are small and stocky with adults reaching a maximum length and weight of 1.8m and 75 kg respectively.[10] 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 and thorax are coloured light grey with darker patches around the eye. The dorsal fin, fluke and dorsal cape are a darker grey to bluish black colour with a band that extends 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] The head is cone shaped with a blunt beak. The dorsal fin is triangular in shape and centred in the middle of the back.
Life history
Information on reproduction is limited for Heaviside's, however they are thought to be comparable to Hector's and Commerson's dolphins.[8] 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.[7]
Group size
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.[7] Nursery groups (exclusively females and calves) are not formed in this species.[11]
Predation
Levels of predation are unknown, however orca (Orcinus orca) are known predators and there is evidence of shark attack from body scars.[12]
Distribution
Geographic range
The species ranges from Cape Point, South Africa along 2,500 km of coastline throughout Namibia and into Southern Angola. Whilst the northernmost limits have yet to be established, several dolphins have been sighted or accidentally caught by fishing vessels north of the Angola-Namibia border,[13][14][15][16] thus lending support for the range extending into Angola. The Benguela current brings cool waters to the coast however, its extent only reaches to the southern extent of Angola. It is likely that Heaviside distribution is limited to the current's area of influence to the region, given their preference for temperate cool water.[4][5] Systematic surveys have dedicated effort to describing the distribution in southern South Africa[11] and current research efforts focus on local populations in Walvis Bay and Lüderitz, Namibia.[17] These locations are also popular hotspots for watching these dolphins in addition to Lambert's Bay and Cape Town, South Africa. Sightings are common from land and there are several dolphin watching tour companies by which Heaviside's 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.[18] 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.[19]
Habitat preferences
Relatively high densities of dolphins are associated with the abundance of their main prey item; juvenile hake (Merluccius capensis). Most commonly sighted within sea surface temperatures of 9-15 °C, depths less than 100m[15] and sandy shores exposed to swell.[11]
Behaviour
Heaviside's dolphins are energetic and social animals. They are attracted to boats and frequently bow-ride.[20] Individuals can also be seen surfing in coastal waves. Iconic vertical leaps clear the water before re-entering headfirst with almost no splash.[7] Heaviside's dolphins use echolocation to find and capture prey.[21]
Diet and Foraging
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) are also consumed.[22] Foraging occurs mostly at the seabed, in shallow depths. Cooperative feeding is rarely observed in the Cephalorhynhus dolphins.[8]
Movement patterns
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.[23] Movement inshore to rest and socialise occurs in the morning.[20] However, the pattern is different in Walvis bay, Namibia where dolphins stay inshore during the night.[24]
Home range and site fidelity
Heaviside's have small home ranges of 50–80 km.[25] Sightings of individuals at the same locations over time suggest a degree of site fidelity.[25][26]
Dive time and depth
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.[27] The maximum dive depth recorded was 147 meters, however the majority of dives were less than 50 meters.[27] Dive duration were predominantly less than 2 minutes with most dives between 0 and 1 minutes (Davis et al. 2014).[27]
Sympatry with other delphinids
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.[11] Where both species overlap in prey selection, Heavisisde's take larger prey items, potentially because they are outcompeted by the larger dusky dolphins for their preferred, small size of prey.[28]
Vocalisations
As is the case with all species in the genus, Heaviside's produce high-frequency narrow-band (HFNB) echolocation clicks (centred around 125–130 kHz), and do not whistle.[29] This adaptation is theorised to allow acoustic crypsis from eavesdropping predators, as the sounds produced are outside of the detectable frequencies of orca.[30] Furthermore, HFNB clicks are limited in range, and thought to provide a foraging advantage in the often cluttered, nearshore environment in which these species occur.[31] Heaviside's also produce a second click type, of lower frequency, that is within the detectable range of orca.[32] These calls are produced most frequently in large 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.[33]
Population status
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.[20] Local population estimates for Walvis bay and Lüderitz are 508 and 494 respectively.[5] High mitochondrial DNA diversity discovered suggests a relatively large population size,[8] however quantification of abundance throughout the range is still required.
Threats
Whilst poorly studied, Heaviside's are exposed to a variety of threats given their limited range in coastal waters subject to a range of anthropogenic activities. Directed catch has occurred historically, with meat being used for human consumption.[34]
Bycatch and hunting
Whilst the dolphins are afforded full legal protection from hunting, direct mortality from fisheries bycatch (employing such methods as purse seine, gillnets, beach seines and trawls) is considered an ongoing, yet unquantified threat.[5] Recently developed mid water trawls for horse mackerel (Trachurus capensis) are considered an emerging threat.[5] Localised hunting may still take place.[5]
Climate change
Heaviside's have been identified as a species whose geographic range will likely contract as a result of climate change.[35] With warming temperatures, all the species in the Cephalorhynchus genus might be expected to seek cooler waters (i.e. move poleward) to which they are adapted. However, these species are likely already bounded to their current distributions at the southernmost extents of their respective landmasses.
Boat interactions
The exposure to and effects of ship strikes, boat traffic and marine tourism have not been quantified for this species, however negative effects have been demonstrated for other coastal cetacean species.
Conservation status
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[36] 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.
Heaviside's dolphins are considered to be one of the most at risk cetacean species from global climate change.[37]
References
Citations
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