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 Striped Dolphin has a broad distribution from tropical and warm temperate regions of the Atlantic, Indian and Pacific Oceans, extending from about 50°N to 40°S. However, extralimital records from the Prince Edward Islands have also been documented. Within the assessment region, its distribution is considered to range in waters deeper than 500 m, from Kosi Bay to Cape Agulhas; although, strandings have been recorded from Mozambique (Tofo Beach: 23°50’S; Ross 1984) to the Western Cape (Yzerfontein). The distribution pattern may be confounded warm-water incursions; when warm-water eddies of the Agulhas Current intrude into cold water and then dissipate, Striped Dolphins that were in that warm water may be unable to survive in cold water and strand further west (e.g. Yzerfontein) than their actual distribution.

Population trend

Trend

No estimates of abundance are available for Stenella species within the assessment region. A detailed analysis of Striped Dolphin standing records are still pending; however, no change in temporal or geographic trends in the frequency of strandings is expected. 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. Similar to other Stenella species, accidental bycatch in pelagic fishing gear has been identified as a threat to Striped Dolphins in other regions (Hammond et al. 2008). Net fisheries in the western Indian Ocean (including drift net fisheries south of Madagascar) may prove to be an emerging, undocumented threat to this species, specifically within pelagic trawls or purse-seine fisheries. As an extension to the assessment by Cockcroft and Krohn (1994), an up-to-date assessment of the potentially dangerous pelagic fisheries off the coasts of Africa may be necessary. Striped Dolphins have also been intermittently recorded entangled in shark nets off the coast off KwaZulu-Natal, but this is unlikely to have any major effect on abundance (Cockcroft 1990).

Since the 19th century, Striped Dolphins have been directly exploited in Japanese waters, in fact, at least 10,000 individuals were caught each year between 1942 and 1953, and approximately 14,000 were taken annually between the late 1950s and early 1960s (Kasuya & Miyazaki 1982). Catches declined during the 1980s and 1990s, and between 1989 and 1993, the average annual catch was 1,028 individuals (Perrin et al. 1994).

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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,]
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