Red List of South African Species

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Least Concern (LC)
Assessors: Simon Elwen Stephanie Plön
Contributors: Shanan Atkins Ken Findlay Mike Meyer Herman Oosthuizen
Reviewers: Claire Relton

Rationale

Large schools and frequent sightings of Dusky Dolphins in both the northern (Namibia) and southern (South Africa) Benguela suggest high abundance and more than 10,000 mature individuals. No major threats were identified, although an emerging threat of mid-water trawling requires monitoring. This species is thus listed as Least Concern. However, as more data is acquired about taxonomy, distribution, subpopulation size and trends, and the levels of bycatch, this species may require reassessment.

Regional population effects: There appears to be a gap in distribution of Dusky Dolphins along the continental shelf around the South Africa–Namibia border that is associated with the Lüderitz Upwelling Cell and Orange River Cone (Best 2007). This hiatus suggests that isolation of animals in South Africa and Namibia may occur.

Distribution

Across the Southern Hemisphere, Dusky Dolphins are widespread but occur in disjunct subpopulations off the coast of South America, the west coast of southern Africa, and New Zealand, with occasional sightings from subAntarctic Islands around Australia (Brownell & Cipriano 1999; Best 2007). They have also been recorded from around the Prince Edward Islands, Gough Island, the Falkland Islands and Amsterdam Island (Van Warebeek et al. 1995).

In the region of assessment, they occur in cool temperate waters on the continental shelf from western False Bay to the Orange River. This species is considered a year- round resident of the west coast of southern Africa, and is located most commonly over the continental shelf, in shallow waters between 0–50 m, but occasionally occurs over the shelf edge (Findlay et al. 1992).

Population trend

Trend

Although direct abundance estimates exist, sighting rates produced during coastal surveys directed at Heaviside’s dolphins show regular occurrence of large groups throughout the southern Benguela, with up to 0.9 groups / km searched seen in St Helena Bay (Elwen et al. 2010). Although not seen as frequently close to shore in Namibia, Dusky Dolphins are amongst the most frequently encountered species on the Namibian continental shelf, and are commonly spotted off South Africa’s west coast (Simon Elwen, Namibian Dolphin Project, unpubl. data). Dusky Dolphins are known to gather in schools of up to 800 (Findlay et al. 1992; Best 2007). The high sighting rate and large group sizes suggest a population of over 10,000 mature individuals.

It remains uncertain whether the groups around oceanic islands, for example, those around the Prince Edward Islands, are discrete or regularly mix with animals in other areas (Brownell & Cipriano 1999). Model-based estimates of generation time are 16.4 years (Taylor et al. 2007).

Threats

This species may be susceptible to both offshore and inshore threats. Globally, Dusky Dolphins are threatened by entanglement in gillnets, particularly in mid-water trawls. In the assessment region, they are caught in midwater trawls, purse-seines and set nets but these are considered a minor threat and mortality numbers are unknown. However, there is an emerging threat related to the mid-water trawling fisheries in the southern Benguela. Both fishermen and cetaceans are drawn to areas of high prey density, and trawling fishing boats often make hunting easier for cetaceans. However, with the benefits of increased feeding success comes the additional risk of entanglement. Trawl fisheries not only influence target species and their immediate predators, but also the rest of the food web. For example, trawl fisheries may directly target Hake (Merluccius spp.), which is a predator of Anchovy, also a common prey item of Dusky Dolphins. Six Dusky Dolphins were reported to have died as a result of bycatch in gillnets during one year between 1986 and 1998 (Best & Meÿer 2010).

A recent collapse (mid-2000s) in South Africa’s Sardine stocks due to overexploitation may threaten prey availability for Dusky Dolphins (Coetzee et al. 2008), and is expected to have resulted in a diet change for this species. Additionally, harmful algal blooms caused by dinoflagellates may be increasing in frequency and severity in the southern Benguela current as a result of climate change (Van der Lingen et al. 2015). This was found to have an indirect effect on the condition of Sardine, a top prey item for this species (Van der Lingen et al. 2015)

Uses and trade

There is no known trade in this species within the region under consideration

Conservation

The species is listed in Appendix II of the Conventional on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and Marine Living Resources Act (No. 18 of 1998). Within the assessment region, this species’ distribution falls within the West Coast National Park MPA. Recent bycatch in gillnets occurs at an unknown level and needs to be investigated. An investigation resolving population structure is required.Taxonomy requires clarification.

No direct research is occurring on Dusky Dolphins in South Africa, other than ongoing recording and dissection of stranded animals attended to by Department of Environmental Affairs (DEA) and the University of Pretoria MRI/South African Museum team. Abundance, habitat use and acoustic behaviour is currently under study in Namibia through the work of the Namibian Dolphin Project (Elwen and colleagues).  

Recommendations for managers and practitioners:
  • Fisheries bycatch occurs at levels that are suspected to be low. The level of bycatch should be clarified and the emerging threat with respect to the midwater trawl sector should be monitored.
Research priorities:
  • More research is required focusing on the distribution of Dusky Dolphins and possible existence of population structure between South Africa and Namibia (see below).
  • Bycatch in commercial fisheries is not well quantified and current estimates are needed, especially for the purse-seine industry in both South Africa and Namibia and the mid-water trawl industry.
  • Taxonomy requires clarification at a global level.
  • Estimate of total population size would be useful to allow a better understanding of the role of Dusky Dolphins as top predators in fisheries models.
  • Research priorities include distribution clarification, and subpopulation abundance and trends. It is necessary to better understand the apparent hiatus in distribution around the Orange River mouth and establish whether the South African and Namibian stocks are separate; there is particular need to gather genetic data from the Namibian animals.
  • The taxonomy of the Dusky Dolphin is unresolved from genus through to subspecies level and requires clarification.
Encouraged citizen actions:
  • Use information dispensed by the South African Sustainable Seafood Initiative to make good choices when buying fish in shops and restaurants, e.g. wwfsa.mobi, FishMS 0794998795.
  • Save electricity and fuel to mitigate CO2 emissions and hence rate of climate change.
  • Buy local products that have not been internationally shipped.
  • Reduce boat speed in harbours.
  • Report sightings on virtual museum platforms (for example, iSpot and MammalMAP) to help with mapping geographical distribution.

References 

[@book{275,
 address = {Cambridge},
 author = {Skinner, J.D. and Chimimba, C.T.},
 publisher = {Cambridge University Press, United Kingdom},
 title = {The Mammals of the Southern African Subregion},
 year = {2005}
}
,@article{2060,
 author = {Coetzee, J.C., Van der Lingen, C.D., Hutchings, L. and Fairweather, T.P.},
 journal = {ICES Journal of Marine Science: Journal du Conseil},
 number = {9},
 pages = {1676--1688},
 title = {Has the fishery contributed to a major shift in the distribution of South African sardine?},
 volume = {65},
 year = {2008}
}
,@inbook{2474,
 address = {San Diego, California, USA.},
 author = {Perrin  and Thewissen },
 booktitle = {Minke Whales <i>Balaenoptera acutorostrata</i> and <i>B. bonaerensis</i>},
 editor = {Perrin, W.F. and Brownell, R.L},
 pages = {750–754},
 publisher = {Academic Press},
 title = {Encyclopedia of Marine Mammals},
 year = {2002}
}
,@electronic{2474,
 address = {www.marinemammalscience.org},
 author = {Committee on Taxonomy},
 publisher = {Society for Marine Mammalogy},
 title = {List of marine mammal species and subspecies},
 year = {2017}
}
,@techreport{2475,
 address = {La Jolla, California},
 author = {Taylor, B.L., Chivers, S.J., Larese, J. and Perrin, W.F.},
 title = {Generation length and percent mature estimates for IUCN assessments of cetaceans},
 year = {2007}
}
,@book{2476,
 address = {Cape Town, South Africa},
 author = {Best, P.B.},
 publisher = {Cambridge University Press},
 title = {Whales and Dolphins of the Southern African Subregion},
 year = {2007}
}
,@book{2762,
 author = {Jefferson, T. A., Leatherwood, S. and Webber, M. A.},
 publisher = {United Nation Environment Programme and Food and Agricultural Organization of the UN},
 title = {Marine Mammals of the World: FAO Species Identification Guide},
 year = {1993}
}
,@article{2762,
 author = {Sekiguchi, K., Klages, N.T.W. and Best, P.B.},
 journal = {South African Journal of Marine Science},
 pages = {843--861},
 title = {Comparative analysis of the diets of smaller odontocete cetaceans along the coast of southern Africa},
 volume = {12},
 year = {1992}
}
,@article{2762,
 author = {Findlay KP, Best PB, Ross GJB, Cockcroft VG.},
 journal = {South African Journal of Marine Science},
 pages = {237–270},
 title = {The distribution of small odontocete cetaceans off the coasts of South Africa and Namibia},
 volume = {12},
 year = {1992}
}
,@article{4161,
 author = {Moloney, C.L., Fennessey, S.T., Gibbons, M.J., Roychoudhury, A., Shillington, F.A. von der Heyden, B.P. and Watermeyer, K.},
 journal = {African Journal of Marine Science},
 number = {3},
 pages = {427--448},
 title = {Reviewing evidence of marine ecosystem change off South Africa},
 volume = {35},
 year = {2013}
}
,@inbook{9249,
 address = {San Diego, CA, USA},
 author = {},
 booktitle = {Pilot whales <i>Globicephala</i> Lesson, 1828},
 editor = {Bernard, H. J. and Reilly, S. B.},
 pages = {245--279},
 publisher = {Academic Press},
 title = {Handbook of marine mammals, Vol. 6: The second book of dolphins and the porpoises},
 year = {1999}
}
,@article{11144,
 author = {LeDuc, R.G., Perrin, W.F. and Dizon, A.E.},
 journal = {Marine Mammal Science},
 pages = {619--648},
 title = {Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences},
 volume = {15},
 year = {1999}
}
,@article{11146,
 author = {Van Waerebeek, K.},
 journal = {Fishery Bulletin},
 pages = {754--774},
 title = {Geographic variation and sexual dimorphism in the skull of the dusky dolphin, <i>Lagenorhynchus obscurus</i> (Gray, 1828)},
 volume = {91},
 year = {1993}
}
,@article{11146,
 author = {Van Waerebeek, K.},
 journal = {Estudios Oceanologicos},
 pages = {37--53},
 title = {External features of the dusky dolphin <i>Lagenorhynchus obscurus</i> (Gray, 1828) from Peruvian waters},
 volume = {12},
 year = {1993}
}
,@article{11146,
 author = {Aguayo, A., Bernal, R., Olavarria, C., Vallejos, V. and Hucke, R.},
 journal = {Revista de Biologia Marina y Oceanografia},
 number = {1},
 pages = {101--123},
 title = {Observaciones de cetáceos realizadas entre Valparaíso e Isla de Pascua, Chile, durante los inviernos de 1993, 1994 y 1995},
 volume = {33},
 year = {1998}
}
,@article{11146,
 author = {Van Waerebeek, K., van Bree, P. J. H. and Best, P. B.},
 journal = {South African Journal of Marine Science},
 pages = {25--35},
 title = {On the identity of <i>Predelphinus petersii</i> Lutken, 1889 and records of dusky dolphin <i>Lagenorhynchus obscurus</i> (Gray, 1828) from the southern Indian and Atlantic oceans},
 volume = {16},
 year = {1995}
}
,@article{11146,
 author = {May-Collado, L., and Agnarsson, I. },
 journal = {May-Collado, L., and Agnarsson, I. },
 pages = {344--354},
 title = {Cytochrome b and Bayesian inference of whale phylogeny},
 volume = {38},
 year = {2006}
}
,@inbook{11146,
 address = {San Diego, CA, USA.},
 author = {Wursig  and Wursig },
 booktitle = {Neglected but not forgotten – Southern Africa’s Dusky Dolphins},
 editor = {Best P., and  Meÿer, M.A.},
 pages = {291--312},
 publisher = {Academic Press},
 title = {Dusky dolphins: Master Acrobats off Different Shores},
 year = {2010}
}
,@inbook{11146,
 address = {San Diego, CA, USA.},
 author = {Wursig  and Wursig },
 booktitle = {Dusky Dolphin life history and demography},
 editor = {Cipriano, F., and Webber, M.},
 pages = {21--48},
 publisher = {Academic Press},
 title = {Dusky Dolphins: Master Acrobats off Different Shores},
 year = {2010}
}
,@article{11146,
 author = {Elwen, S.H., Thornton, M., Reeb, D., and Best, P.B.},
 journal = {African Zoology},
 pages = {78--91},
 title = {Near-shore distribution of Heaviside’s (<i>Cephalorhynchus heavisidii</i>) and Dusky Dolphins (<i>Lagenorhynchus obscurus</i>) at the southern limit of their range in South Africa},
 volume = {45},
 year = {2010}
}
,@article{11146,
 author = {Harlin-Cognato, A.D., Markowitz, T., Würsig. B., and Honeycutt, R,L.},
 journal = {BMC Evolutionary Biology},
 pages = {131},
 title = {Multi-locus phylogeography of the Dusky Dolphin (<i>Lagenorhynchus obscurus</i>): passive dispersal via the west-wind drift or response to prey species and climate change?},
 volume = {7},
 year = {2007}
}
,@electronic{11146,
 address = {http://www.iucnredlist.org},
 author = {IUCN (International Union for Conservation of Nature)},
 publisher = {The IUCN Red List of Threatened Species. Version 3.1},
 title = {<i>Lagenorhynchus obscurus</i>},
 year = {2008}
}
,@article{11146,
 author = {van der Lingen CD, Hutchings L, Lamont T, Pitcher GC},
 journal = {Environmental Development},
 title = {Climate change, dinoflagellate blooms and sardine in the southern Benguela Current Large Marine Ecosystem},
 volume = {DOI:10.1016/j.envdev.2015.09.004},
 year = {2015}
}
,@article{11146,
 author = {Vaughn RL, Shelton DE, Timm LL, Watson LA, Würsig B},
 journal = {New Zealand Journal of Marine and Freshwater Research},
 pages = {391--400},
 title = {Dusky Dolphin (<i>Lagenorhynchus obscurus</i>) feeding tactics and multi-species associations},
 volume = {41},
 year = {2007}
}
,@article{11146,
 author = {Wursig B, Wursig M},
 journal = {Fish. Bull },
 pages = {871--890},
 title = {Behavior and ecology of the Dusky Dolphin, <i>Lagenorhynchus obscurus</i>, in the South Atlantic},
 volume = {77},
 year = {1980}
}
,]
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