Red List of South African Species

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Least Concern (LC)
Assessors: Stephanie Plön Vic Cockcroft
Contributors: Claire Relton Shanan Atkins
Reviewers: Matthew Child

Rationale

Although no data on population dynamics are available for Risso’s Dolphins, there are no major threats that could cause a range-wide decline and this species is not a conservation priority. The biggest threat within the assessment region, the Chokka fishery, is localised and is not suspected to impact the population negatively. However, this threat should be monitored. Currently, they are listed as Least Concern, in line with the global assessment.

Regional population effects: Risso’s Dolphin is a wide-ranging, pelagic species, and although their movements and seasonality are largely unknown, no barriers to dispersal have been recognised, thus rescue effects are possible.

Distribution

Risso’s Dolphins are located extensively throughout tropical and temperate regions of both the southern and northern hemisphere, predominantly in waters more than 1,000 m deep on the continental slope, but also have an apparent preference for the steep continental shelf edges between 400–1,000 m deep (Kruse et al. 1999; Baird 2002). Within the assessment region, this species has been recorded along the shelf edge, between 31°S on South Africa’s west coast, and 29°S on the east coast (Skinner & Chimimba 2005). Along the west coast, sightings have been reported from Saldanha Bay, and strandings between 23°S and 21°S have been recorded from Namibia (Findlay et al. 1992). On the east coast, Risso’s Dolphins have been documented well offshore, along the 1,000 m isobath (Ross 1984).

Population trend

Trend

No global population estimates or trends are available for Risso’s Dolphins, and although some regional estimates exist for other areas (Baird 2002), there are none for the assessment region. However, based on the frequency of strandings (approximately 8 per year on South Africa’s east coast), a relatively high population abundance is expected in South African waters. Generally, in regions were their ranges overlap, Risso’s Dolphins are more abundant than other closely related cetaceans, including pilot whales (Globicephala spp.), False Killer Whales (Pseudorca crassidens), Melon-headed Whales (Peponocephala electra) and Pygmy Killer Whales (Feresa attenuata) (Baird 2002). Taylor et al. (2007) estimated a generation period of 19.6 years for this species.

Threats

The Chokka Squid (Loligo vulgaris reynaudii) is the second most important prey species, in terms of numbers and frequency, and the most important species in terms of mass (S. Plön, unpubl. data). Thus competition with the Chokka fishery could pose a real threat to this species, however, currently this has not been documented and no direct observations have been made. Linked to this, Risso’s Dolphins sometimes remove bait from longline fisheries, thus they are occasionally deliberately shot by aggravated fishermen. The inshore area utilised by the Chokka fishery is only a small part of this species’ range, thus it is suspected to be a minor threat. In other parts of its range, this species has been recorded as accidental bycatch in gillnet and seine-net fisheries (Baird 2002).

Similar to beaked whales, this species may be vulnerable to marine noise pollution produced by, for example, navy sonar and seismic exploration (Cox et al. 2006). Additionally, the increasing risk of plastic pollution (Baird 2002) and global climate change (Learmonth et al. 2006) should also be recognised as minor threats to this species, although the severity of these impacts requires confirmation.

Uses and trade

Although historical exploitation of this species has been documented in Japanese waters (Mitchell 1975b), there is no trade or use of this species within the assessment region.

Conservation

Risso’s Dolphin is listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and this species is protected by the Marine Living Resources Act (No. 18 of 1998) of the national legislation. No species-specific conservation measures have been recognised. However, based on the likelihood of depredation on longline and Chokka fisheries, and the resulting persecution of this species by local fishermen, systematic monitoring of this species is required. Additionally, continued research into the general ecology and severity of threats to this species would be beneficial.

Recommendations for managers and practitioners:
  • Systematic monitoring of this species in the assessment region, particularly with regards to their interactions with long-line and Chokka fisheries.
Research priorities:
  • The severity and potential impacts of threats, specifically the impacts of competition, bycatch and persecution with fisheries.
  • Population status and trends in abundance.
  • The general ecology of Risso’s Dolphins off South Africa.
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.
  • Save electricity and fuel to mitigate CO2 emissions and hence, the rate of climate change.
  • Buy local products that have not been shipped.
  • Report sightings on virtual museum platforms (for example, iSpot and MammalMAP) to help with mapping geographical distribution. Sightings data from pelagic commercial tourism operators may be particularly valuable.
  • Report any strandings to the relevant local authorities.

References 

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,]
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