Red List of South African Species

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Least Concern (LC)
Assessors: Stephanie Plön Claire Relton Vic Cockcroft
Contributors: Simon Elwen Ken Findlay Michael Meÿer
Reviewers: Shanan Atkins Matthew Child

Rationale

Stenella species have not been well studied in the assessment region and population size and trend estimates are unavailable. However, periodic but regular strandings suggest that there is no major population decline of these species. Additionally, Pantropical Spotted and Spinner Dolphins are considered to be abundant in the Indian Ocean. Although general pelagic threats may apply and annual takes of Stenella species occur in regions outside of the assessment region, no major threats were identified for these species; thus they are not considered conservation priorities. However, the potential emerging threat of a drift-net fishery requires monitoring. The listing as Least Concern is retained for S. attenuata, S. coeruleoalba and S. longirostris.

Regional population effects: No barriers to dispersal of these species have been identified, thus rescue effects are possible.

Distribution

Generally, Stenella species occur in tropical and subtropical waters, but the extent of their range is poorly known in many regions (Moreno et al. 2005). The Pantropical Spotted Dolphin ranges extensively across all oceans from approximately 40°N to 40°S, although it is considerably more plentiful within the lower-latitude regions of its distribution. It occurs in tropical and warm temperate waters. In the assessment region, strandings have been recorded along the KwaZulu-Natal coast in the region of St Lucia from 28°24’S to 29°50’S. Additionally, sightings from the Durban whaling ground have been documented in waters between 200 m and 2,000 m deep, as far south as 32–33°S (Findlay et al. 1992). Additionally, this species has been documented in the southwest Indian Ocean (20°43’S–35°30’S) in summer (Gambell et al. 1975). Although, this species appears to be primarily restricted to South Africa’s east coast, exceptions have been documented as strandings near Gansbaai (34°40’S; 19°30’E), Yzerfontein (33°15’S; 18°07’E) and Varkvlei (32°46.5’S; 18°06’E) in the Western Cape (Findlay 1989). These exceptions may indicate that this species occurs offshore of South Africa’s west coast, or may represent individual strays from the east coast population, as supported by the absence of additional sightings records from the west coast.

Population trend

Trend

No estimates of abundance are available for Stenella species within the assessment region. Regular stranding data of Pantropical Spotted Dolphins suggests that there is no population decline: overall there have been 35 records of strandings or bycatych in KwaZulu-Natal since the 1980s. This is unlikely to be an isolated population as the species travels large distances and may interact with groups from Mozambique and the Mozambique Channel, where several thousands have been sighted. Model based estimates of generation time for the Pantropical Spotted Dolphin and Spinner Dolphin have been recorded at 23.1 years and 13.7 years, respectively (Taylor et al. 2007). For the Striped Dolphin generation time calculated on sexual maturity is 8–9 years, longevity was calculated at 42 years and a calving interval of 2–3 years was recorded (Kroese 1993).

Threats

The offshore distribution of Stenella species within the region suggests that industrial activity is not a major threat, additionally MacLeod (2009) predicted that due to the tropical distribution of S. attenuata and S. longirostris, it is unlikely that these species would be negatively influenced by the effects of climate change. However, although it is largely undocumented, due to their diet and distribution, localized threats to these species include accidental bycatch and competition for prey resources associated with pelagic fisheries. Although within the assessment region there appears to be no major overlap between this species and major fishing operations, the Pantropical Spotted Dolphin in the eastern Pacific is severely threatened by tuna-seine fisheries. In fact, in 1972 approximately 270,000 Spotted Dolphins were incidentally killed due to accidental bycatch (Perrin et al. 1982). Gear modifications, which enabled dolphins to escape more easily aided in the decline of bycatch, though mortalities of 55,000–60,000 individuals in 1987 (Hall & Boyer 1989) and 15,000–16,000 individuals in 1992 (Hall & Lennert 1997) were recorded. Additionally, elsewhere in the world (such as off Japan), this species is directly targeted in drive fisheries; a catch of 4,184 individuals was recorded in 1978 (Miyazaki 1983).

Uses and trade

There is no trade of these species within South Africa, although in certain regions Stenella spp. are hunted for food and as bait for fisheries.

Conservation

No species-specific conservation initiatives have been identified for Stenella species within the assessment region, although S. attenuata, S. coeruleoalba and S. longirostris are all listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and are protected by national legislation under the Marine Living Resources Act (No. 18 of 1998).

Ship-based sighting surveys are recommended for the assessment region in order to determine general abundance, seasonality and distribution of Stenella species, and the pelagic zone of the temperate Agulhas Current should be specifically targeted. Additionally, investigations into the severity of threats and possible mitigation measures (including the use of alternative fishing gear technologies) associated with pelagic trawl, gillnet and purse-seine fisheries are required for these species. In response to the negative effects associated with fisheries bycatch of other dolphin species, Buscaino et al. (2009) suggest a collaborative response towards sustainable exploitation of oceanic resources, a decrease in the intensity of marine extraction and the establishment of protected areas.

Recommendations for managers and practitioners:
  • Accurate bycatch assessments in the pelagic trawl, gillnet and purse-seine fisheries.
  • Enforce regulations associated with deep water fisheries, including bycatch mitigation efforts.
  • Sightings data should be recorded during systematic monitoring of other marine species.
Research priorities:
  • Basic life history parameters, population size, structure and trends within the assessment region.
  • Bycatch assessments in pelagic fisheries, including a specific reassessment of the western Indian Ocean fisheries.
  • Taxonomic resolution of the Stenella genus.
  • Distribution and the identification of core concentration regions of these species within South African waters.
Encouraged citizen actions:
  • Use information dispensed by the South African Sustainable Seafood Initiative (SASSI) to make good choices when buying fish in shops and restaurants, e.g. wwfsa.mobi, FishMS 0794998795.
  • Report sightings on virtual museum platforms (for example, iSpot and MammalMAP) to help with mapping geographical distribution.
  • Report any stranding reports to the relevant local authorities.

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 title = {Age, growth and reproductive biology of striped dolphins, <i>Stenella coeruleoalba</i> (Meyer, 1833) off the coast of southern Africa. M.Sc. Thesis.},
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,@article{20729,
 author = {Perrin WF, Henderson JR.},
 journal = {Reports of the International Whaling Commission (Special issue)},
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 volume = {6},
 year = {1984}
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,@article{20729,
 author = {Perrin, W.F., Smith, T.G. and Sakagawa, G.T.},
 journal = {Mammals of the Seas. FAO Fish },
 number = {4},
 pages = {67–83},
 title = {Status of populations of spotted dolphin, <i>Stenella attenuata</i>, and spinner dolphins, <i>Stenella longirostris</i>, in the eastern tropical Pacific},
 volume = {Ser.5},
 year = {1982}
}
,]
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