Red List of South African Species

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

Rationale

Global and regional population trends and abundance data is unavailable for this species, and it is considered elusive and rare in the waters of the assessment region. Although, occasional mass stranding events have been documented in South Africa, it is suspected that these are accredited to natural causes, rather than anthropogenic activities. No major threats that may cause substantial population depletion, have been identified, resultantly, this species is listed as Least Concern, in line with the global assessment. However, considering the rarity and low reproductive potential of the False Killer Whale, it may be particularly vulnerable to minor threats, including fisheries bycatch (especially longline fisheries) and persecution, competition for prey resources, climate change and anthropogenic pollution. Continued research into potential risks, population abundance and distribution, as well as the identification of critical habitats may be necessary.

Regional population effects: The False Killer Whale is a wide-ranging pelagic cetacean, with a continuous distribution and no obvious barriers to dispersal, thus rescue effects are possible.

Distribution

False Killer Whales are widely distributed across the globe, predominantly occurring within deep tropical and warm temperate regions (usually in waters more than 25°C), but unlike the Killer Whale (Orcinus orca), they only very occasionally roam into colder waters (below 20°C) (Mitchell 1975). Their worldwide range is thought to extend from 50°N to 50°S (Odell & McClune 1999). Within southern African waters, this species has been documented off the coast of Lüderitz, Namibia, and from St Helena Bay to the north coast of KwaZulu-Natal (Findlay 1989). A pod of six was recorded off the coast of KwaZulu-Natal, at 29°02’ S; 32°02’ E (Bruyns 1969). This species has been frequently sighted in association with large groups of Common Bottlenose Dolphins (Tursiops truncatus) in the waters of Plettenberg Bay, Eastern Cape.

Population trend

Trend

There are no global estimates of abundance available for this species, however approximately 39,800 (CV = 64%) individuals have been estimated in the eastern tropical Pacific (Wade & Gerrodette 1993), about 16,000 (CV = 26%) within the coastal waters of China and Japan (Miyashita 1993), and around 1,038 (CV = 71%) in the northern Gulf of Mexico (Mullin & Fulling 2004). 

There are no estimates of abundance for the assessment region, as very little sighting data exists. However, a number of mass stranding events have been documented on South Africa’s west coast, for example, 120 individuals at Kommetjie in 1928, more than 200 near Mamre in 1935, and at St Helena Bay, 58 in 1936 and 65 in 1981 (Skinner & Chimimba 2005). All of these mass stranding events took place between August and December.

Threats

No major threats to this species have been identified within the assessment region, however considering that  this species is naturally rare in most regions and some evidence of lower reproductive rates in the southern African region compared to other areas, even low levels of mortality and serious injury, could cause detrimental impacts to local populations. In South Africa, seasonal strandings (between August and December) have been recorded since 1920, all before anthropogenic sounds became a threat to marine animals. As a deep-water species, shallow water may cause disorientation, leading to stranding. Given these facts, it is highly probable that the strandings are not the result of anthropogenic activity and are more likely attributed to natural causes, for example, confusing acoustic reflection within sea canyons. A number of minor threats have been identified:
  1. Fisheries bycatch: Studies have found that this cetacean is more vulnerable than any other to dangerous interactions with Hawaiian long-line fisheries (Forney & Kobayashi 2007). They take fish off long-line hooks and may be incidentally caught, leading to drowning, injury and/or subsequent death when hooks are lodged inside the mouth or gullet (Forney & Kobayashi 2005). In 2005, average rates of depredation of swordfish by False Killer Whales was estimated at 2,999–4,804 in the Atlantic, 509-2,706 in the Indian, and 114–348 in the Pacific Oceans (Ramos -Cartelle & Mejuto 2008). A number of individuals in the coastal waters off Hawaii have scars consistent with wounds inflicted by long-line fishing equipment (Baird & Gorgone 2005). Additionally, this behaviour often leads to persecution and shootings by fishermen, as seen in Killer Whales, in order to decrease depredation and limit economic loss (Ramos-Cartelle & Mejuto 2008).
  2. Competition with fisheries: Overexploitation of large fish species, such as tuna and swordfish by fisheries, causing a decline in prey biomass and size, has been recognised as an additional and increasing threat to this species in Hawaii (Oleson et al. 2010). It is likely that this threat may be extrapolated to other regions of this species’ range, because False Killer Whales target many of the same fish and squid species as commercial fisheries (Ramos-Cartelle & Mejuto 2008).
  3. Anthropogenic pollution: Plastic pollution is a widespread and increasing problem within all oceans. The ingestion of plastic debris has been documented in stranding records of False Killer Whales (Baird 2002), and is a fairly common phenomenon in similar species (Stamper et al. 2006), and those that commonly feed on cephalopods. Finally, the bioaccumulation of persistent organic pollutants (POPs) within the body tissues of False Killer Whales may put this species at risk of diminishing reproductive potential and immunosuppression (Oleson et al. 2010). As long-lived top predators, the risk of exposure to organic pollutants is increased, compared to other species that feed at lower trophic levels (Oleson et al. 2010). Aside from in Hawaii, there  is limited data documenting the concentrations of POPs in False Killer Whales. Although reports of high concentrations of toxins contained within the blubber of False Killer Whales stranded off Canada (Jarman et al. 1996), Taiwan (Chou et al. 2004) and Japan (Haraguchi et al. 2006) have been recorded.

Uses and trade

There is no contemporary trade or use of this species in South Africa.

Conservation

The species is listed in Appendix II of the Convention on Internation Trade I Endangered Species of Wild Fauna and Flora (CITES) and protected by the Marine Living Resources Act (No. 18 of 1998) of the national legislation. 

Considering the substantial interaction rate and vulnerability of this species to longline fisheries in Hawaiian waters, investigations into the bycatch associated with South Africa’s longline fisheries is imperative for this species. Unfortunately, bycatch is often discarded overboard and unrecorded, therefore hindering the documentation of abundance estimates, and the quantification of this threat. Sustainable mitigation of cetacean bycatch is only possible if accurate records regarding fishing techniques and equipment, geographic distribution, season and quantitative data of bycatch is recorded. Additionally, fatally injured individuals may be valuable for dissection in order to enhance the scientific study into the ecology and morphology of this poorly known species.

The current lack of abundance and distribution data for this species within the assessment region, currently prevents the implementation of species-specific mitigation actions, however, it is likely that this species may benefit from the development and expansion of marine protected areas developed with other cetaceans in mind, as they are frequently sighted in association with other cetacean species. The implementation of seasonal and geographic longline fishery exclusion zones of ‘critical habitat’ in areas of high cetacean concentration, such those developed for False Killer Whales in Hawaii since 1992, may reduce False Killer Whale mortality and injury associated with fishery interactions. Critical habitats should be carefully considered and associated with primary feeding and reproduction areas, which are protected from disturbance (Baird et al. 2012).

Recommendations for managers and practitioners:
  • Accurate bycatch assessments in the longline fishery.
  • 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:
  • Population size and trend estimates for the assessment region.
  • Threats to this species in relation to long-line fisheries.
  • Identification of high concentration areas, and critical habitats in South African waters, including distributional limits, seasonal movements and diving behaviour.
  • Diet, reproduction and general biology.
  • Cumulative impacts of anthropogenic influences, such as pollution, commercial fisheries and persecution.
Encouraged citizen actions:
  • Report sightings on virtual museum platforms (for example, iSpot and MammalMAP) to help with mapping geographical distribution. 
  • 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.
  • Buy local products that have not been shipped.
  • Avoid using plastic bags.
  • Report any stranding reports to the relevant local authorities.

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,]
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