Red List of South African Species

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

Rationale

Although this species is frequently sighted in Antarctic waters, and has a circumpolar and widespread distribution, it is one of the least-known of all dolphin species. This species is considered fairly abundant within its range, and no major threats have been recognised. Thus, in line with the global assessment, the Hourglass Dolphin is listed as Least Concern within the assessment region.

Regional population effects: The Hourglass Dolphin is wide-ranging throughout the pelagic waters of the southern oceans, and no obvious barriers to dispersal have been identified, thus rescue effects are possible.

Distribution

The Hourglass Dolphin has a circumpolar distribution within the higher latitudes of the Southern Ocean (Goodall 1997; Goodall et al. 1997; Brownell & Donahue 1998). It is one of three species of delphinid which is considered truly Antarctic (Boyd 2002), and the only delphinid regularly occurring in the Antarctic Polar Front (Brownell & Donahue 1998). They predominantly inhabit sub-Antarctic and Antarctic waters between 45° and 67°S, and although primarily occur offshore, they are occasionally sighted along banks or islands (Goodall 1997, 2002). A recent study into the occurrence of Hourglass Dolphins in the south-west Atlantic and Southern Oceans (Dellabianca et al. 2012) found the presence of two group separated by environmental conditions. The first of these groups occurs in shallow, coastal waters, while the other is primarily located in deeper, colder regions offshore (Dellabianca et al. 2012). Other localised concentrations have been identified around the southern tip of South America, South Georgia, the Falkland Islands (Goodall 1997; Goodall et al. 1997), and north of the South Shetland Islands in the southern Drake Passage (Santora 2012). Although the northern extent of its range is uncertain (there are occasional records from around 33°S), the southern parameters of its distribution extends to the ice-edges in the south. Within the assessment region, this species occurs around the Prince Edward Islands. The Hourglass Dolphin is the only small delphinid that regularly frequents areas south of the Antarctic Convergence and along the Agulhas Current.

Population trend

Trend

There are no recent global estimates of abundance for this species, although Kasamatsu and Joyce (1995) integrated abundance and distribution data collected during sighting surveys from 1976/77 to 1987/88, generating a population estimate for the region south of the Antarctic convergence  of 144,300 (CV = 17%). Additionally, during the southern hemisphere Minke Whale Assessment Cruises (IWC/ IDCR), which took place between 1978/79 and 1987/88, 233 schools of Hourglass Dolphins were recorded, including a total of 1,634 individuals (Kasamatsu et al. 1990). No records of abundance are available for the assessment region, where they occur around the Prince Edward Islands.

Threats

There is very little anthropogenic influence within their distribution and hence there are no known major threats to this species. However, there may be some risk of entanglement in deep-sea fisheries set in the southern oceans, even though records of this are extremely rare. A Japanese experimental drift net fishery, which was set for squid in the southern Indian Ocean, incidentally caught at least one individual (Brownell & Donahue 1998).

MacLeod (2009) suggests that some cetacean species are more vulnerable to the effects of climate change than others, due to certain ecological characteristics, such as a preference for non-tropical regions and shelf waters, which are exhibited by most porpoises and Lagenorhynchus species. In fact, a framework for assessing predicted range changes in response to climate change revealed that 60% of Lagenorhynchus species have a high risk of extinction of at least one population (MacLeod 2009). Additionally, a range contraction is predicted for Hourglass Dolphins, as they are expected to track a range of water temperatures, to which they are adapted. Furthermore, indirect effects of climate change include changes in prey availability, which in turn, may affect dolphin abundance, distribution, movement patterns, social structure, reproductive rate, as well as their susceptibility to disease and the build-up of toxins (Learmonth et al. 2006)

Uses and trade

Although one scientific sample was collected during commercial whaling operations, and a number of other individuals have been caught during research cruises (Brownell & Donahue 1998), there is considered to be no contemporary trade or use of this species.

Conservation

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) listed the Hourglass Dolphin on Appendix II, and this species is also protected by national legislation under the Marine Living Resources Act (No. 18 of 1998). Although no species-specific conservation initiatives have been identified for the Hourglass Dolphin, it is likely that this species would benefit from the ongoing collection of sightings records during ship-based surveys directed at other species, in order to monitor the abundance and distribution of this unfamiliar species. Additionally, comprehensive data collection of bycatch in deep-sea fisheries is necessary in order to determine the severity of this threat to Hourglass Dolphins within the assessment region.  

Recommendations for managers and practitioners:
  • Accurately assess bycatch in the Southern Ocean deep-sea fisheries.
  • Enforce regulations associated with deep water fisheries, including bycatch mitigation efforts.
  • Record sightings data during systematic monitoring of other marine species.
Research priorities:
  • Taxonomic resolution of the Lagenorhynchus genus.
  • Basic life history parameters, population size, structure and trends within the waters around the Prince Edward Islands.
  • Bycatch assessments in deep-sea Southern Ocean fisheries.
  • Current threats, including possible range shifts or indirect effects on prey resources, associated with global climate change.
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.  

References 

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,]
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