Red List of South African Species

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

Rationale

This is the only near endemic cetacean species within the assessment region, ranging northwards along the west coast of southern Africa from Cape Point to southern Angola. Recent research indicates a large population within the assessment region: estimated population size is 6,345 individuals (95% CI 3,573–11,267) along ~ 390 km of coastline from Table Bay to Lambert’s Bay. Thus, we infer that there are certainly > 1,000 mature individuals within the assessment region and possibly > 10,000 mature individuals along the entire west coast of the assessment region. Although we suspect that competition with hake (Merluccius spp.) fisheries could represent a threat to this species, this is indirect, as Heaviside’s Dolphins target smaller-sized prey and remain largely inshore of the fishery. A potential emerging threat is the experimental mid-water trawl fishery for horse mackerel operating of the West Coast. Heaviside’s Dolphin bycatch must be monitored and the potential effects of the full-scale operation should be mitigated if it potentially increases mortality of the species in the future. As this species is limited by water temperature, climate change represents an additional emerging threat. A recent population viability analysis indicated that the population may decline if 63 animals per year are removed (assuming population size is 10,000 individuals), which emphasises the need to quantify mortality rates.

At present, there is no evidence for population decline and thus we list the species as Least Concern. Long-term monitoring of population size and trends is recommended to detect any significant effects of identified threats to this flagship cetacean species. This species should be re-assessed when mortality rates from bycatch and/or subpopulation trends have been quantified.

Regional population effects: The lack of definite population structure between South African and Namibian Heaviside’s Dolphin populations suggests dispersal between the two regions. Furthermore, subpopulation estimates from two high-use areas in Namibia (Walvis Bay: 508 individuals, 95% CI 461–833, and Lüderitz: 494 individuals, 95% CI 403–607) suggest a stable extra-regional population.

Distribution

Heaviside’s Dolphins are near endemic to South African waters and non-migratory. They are restricted to the cold continental shelf waters of the Benguela ecosystem off southwestern Africa, where they are found in waters between the surf zone and 200 m depth, although most records occur in less than 100 m of water (Findlay et al. 1992; Best 2007). The northernmost record occurs at 16° 30’S (Baia dos Tigros, southern Angola) and the southernmost record at the southwestern tip of the continent (34° 20’S) at Cape Point (Best 2007). The cetacean fauna of Angola is poorly known and it is uncertain how far north the species’ distribution extends, but it is likely that the distribution is closely linked to the cool waters of the Benguela ecosystem. Records available from both summer and winter surveys in the in the coastal waters of the Namibe Province, Angola (15° 33’S), do not include sightings of the species (Weir 2010). Although sightings have occurred in the warmer waters to the east of Cape Point, these are considered vagrants (Best 2007; Vinding et al. 2015). Within the assessment region specifically, the species’ range extends from the continental shelf waters off Cape Point to the Orange River. They appear to occur continuously along the coast within this geographic range, with areas of higher density associated with higher levels of prey availability in both South Africa (Elwen et al. 2010) and Namibia (Golaski 2015).

Population trend

Trend

No range-wide survey has been conducted for this species. However, population estimates are available at several spatial scales from photographic mark-recapture studies over three years (1999–2001) between Cape Town and Lambert’s Bay, South Africa: 527 animals (95% CI 272–1,020) using 20 km of coastline in western St Helena Bay estimated over 6 weeks of survey effort; using 150 km of coastline around St Helena Bay, estimated over three summer seasons: 3,429 animals (95% CI 1,721–6,828); and using ~ 390 km of coastline from Table Bay to Lambert’s Bay, estimated between two summer field seasons: 6,345 animals (95% CI 3,573–11,267) (Elwen et al. 2009b). Considering the fact that Table Bay to Lambert’s Bay represents roughly half the length of the west South African coastline, doubling this estimate would yield a total of 12,690 individuals within the assessment region. This estimate may be likely given the small home ranges, apparently continuous distribution within the overall range, and the size of estimates available for the widely spaced areas mentioned above. Corroborating this are population estimates from two high-use areas in Namibia (Walvis Bay: 508 animals, 95% CI 461–833, over eight weeks; and Lüderitz: 494 animals, 95% CI 403–607, 14 survey days over one year). Similar densities exist in the northern Benguela (S. Elwen et al. unpubl. data). Although no data are currently available to estimate a population trend, we suspect the population is stable due to its large size and relatively minor threats. However, a recent population viability analysis indicated that the population may decline if 63 animals per year are removed (assuming the population size is 10,000 individuals), which emphasises the need to quantify mortality rates (Gopal 2014).

The population genetic structure and gene flow investigated for this species using both mitochondrial control region sequences and thirteen microsatellite loci along the South African (Table Bay, St. Helena Bay, Lambert’s Bay, Hondeklipbaai, and Port Nolloth) and Namibian (Luderitz and Walvis Bay) coastline rejected the hypothesis of one homogenous population, but were somewhat contrasting. Mitochondrial DNA suggested six subpopulations of the seven sites sampled from Cape Town, South Africa, to Walvis Bay, Namibia, with Hondeklipbaai and Port Nolloth sampling sites grouping as one subpopulation, whilst microsatellite data identified two metapopulations, namely a southern group consisting of Table Bay and St. Helena Bay and a northern group consisting of Lambert’s Bay, Hondeklipbaai, Port Nolloth, Luderitz and Walvis Bay (Gopal 2014). These results suggest that there are two larger subpopulations, but that, even within these, gene flow is somewhat limited between major bays (Gopal 2014). Further genetic research including information on relatedness, kin associations and mating patterns will enhance the population-level status by identifying important management units for conservation.

Threats

Heaviside’s Dolphins are suspected to face fewer threats than many other cetacean species due to limited human population density on the West Coast and the lack of direct competition with the hake industry. The following minor threats are described and should be quantitatively evaluated for their effect on the species:
  1. Direct mortality from bycatch is probably the largest threat. They are susceptible to entanglement in inshore fishing gear, such as beach seines, purse seines, trawls and gillnets (Best & Abernethy 1994; Peddemors 1999; Elwen et al. 2010). Numbers killed are unknown, but are believed to be < 100 annually, because of short soak times of nets. However, this could be an underestimate, because fishermen may hide the carcasses (Best & Abernethy 1994). A potential emerging threat is the experimental mid-water trawl fishery for horse mackerel operating off the West Coast. Heaviside’s Dolphin bycatch must be monitored and the potential effects of the full-scale operation should be considered if it might significantly increase mortality of the species in the future.
  2. A potential threat is competition with hake (Merluccius spp.) fisheries, which may reduce the prey base or kill animals as bycatch. There is no direct competition for hake as these dolphins target a smaller size class than the commercial fisheries (Sekiguchi et al. 1992). Furthermore, since Heaviside’s Dolphins occur mainly in waters less than 100 m deep, there is little overlap with the commercial hake bottom trawl, which occurs in waters between 100–1,000 m (Fairweather et al. 2006). Since the fishery is well managed and the stocks in South Africa and Namibia are considered sustainable (by the Marine Stewardship Council), although well below pristine levels (van der Westhuizen 2001; Rademeyer et al. 2008), there is no reason to expect a current or increasing threat to Heaviside’s Dolphins from the fishery.
  3. Although there is no evidence for an overall population decline at present, small home range size may facilitate local declines and climate change may exacerbate existing threats. Significant changes in marine ecosystems have already been recorded in terms of air and sea temperatures, wind patterns, ocean current speed and upwelling regimes (Mead et al. 2013; Moloney et al. 2013). Heaviside’s Dolphins are limited by water temperatures that are either too cold or too warm (so-called CWWL species) and are listed amongst the species most vulnerable to climate change (MacLeod 2009).
  4. Although fully legally protected, some direct illegal harvesting has been reported in the past (Rice & Saayman 1984; Best & Abernethy 1994), but there are no known records of this recently.
  5. Concern has been expressed about the potential effects of boat traffic and pollution (Culik 2005; MacLeod 2009). Although behavioural changes in response to boat traffic have been identified in some areas in Namibia (Elwen et al. in review; MacLeod 2009), low human population densities and the scarcity of large ports along most of the species’ range probably help reduce the possibility of adverse effects from boat traffic at a population level (P. Best pers. comm. 2013).
  6. Organochlorine levels in a small sample of Heaviside’s Dolphins failed to indicate significant exposure to DDT in the coastal waters of South Africa’s west coast, where the scarcity of arable land and low rainfall may help minimise pesticide residue inputs to the marine environment (de Kock et al. 1994). A more recent analysis of heavy metals in the skin of Heaviside’s Dolphins from South Africa and Namibia revealed that, while levels were higher than expected for some metals, sampled individuals were deemed to be at relatively minimal risk of lethal poisoning (Serot 2013). Additionally, clear differences between sampling sites were detected, thereby corroborating the existence of population structure and small home range.
Population viability analysis (PVA) is a commonly used tool to forecast extinction risk as well as assessing a species’ threat category, whereas sensitivity analyses consider the effects that changes in demographic parameters (population size, age, birth and death rate and migration) or environmental variations can have on the resilience of wildlife populations, and the effect of different management approaches that can be tested. Sensitivity analysis was examined with various hypothetical scenarios whereby demographic parameter values were varied to examine potential population responses to threats. The modelled PVA exercise was inconclusive, because parameter values used were based on a threatened sister species, Cephalorhynchus hectori, and did not produce models that showed stable populations, suggesting these values do not apply to Heaviside’s Dolphin. However, when the model parameters were modified to produce a stable population, simulated rates of removal (for example, from bycatch and/or illegal harvesting) suggested that the population might decline under removal rates of 63 animals per year if population size is 10,000 individuals. Because of the seriousness of this modelling result, there is an urgent need for long-term life history data, inclusive of the direct and indirect threats faced by this species, to completely understand the biology and behaviour of the population (Gopal 2014).

Uses and trade

Some illegal hunting has been reported, but it is probably not at a significant level (Best & Abernethy 1994; Best 2007). There is presently no known trade in the region, although some localised, illegal hunting or opportunistic use of by-caught animals may still take place on the South African west coast.

Conservation

This species occurs in the West Coast National Park Marine Protected Area (MPA) and is listed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the Marine Living Resources Act (No. 18 of 1998). Suggested interventions are further establishments of MPAs along the west coast, stricter regulation of the hake and horse mackerel fisheries, and zoning of boat traffic in high-density use areas, such as Granger Bay, Cape Town:
  1. MPAs would be best established at Table Bay, Yzerfontein or Lambert’s Bay where Heaviside’s Dolphin abundance is highest, due to the use of predictable breeding and foraging sites.
  2. Inshore net management of fisheries can be achieved by assessment of risk to dolphin populations and education of artisanal fishers.
  3. Zoning boat traffic could be achieved by relating traffic patterns to dolphin high-use areas and activity patterns, where boat traffic is restricted between 06h00 and noon when dolphins are most likely to be closest to the shore (Elwen et al. 2009a).
More research emphasis should be placed on possible detrimental interactions due to tour vessels and the overfishing of prey stocks, especially hake, and resilience of the species to adapt to alternate prey. Increased knowledge of how Heaviside’s Dolphins respond to boat traffic and the impact of this at a subpopulation level would be informative to potentially modify vessel behaviour/area use and reduce impacts.

Recommendations for managers and practitioners:
  • The systematic monitoring of identified subpopulations to determine subpopulation size and trends is recommended. Both line-transect (Slooten et al. 2006) or mark-recapture (Gormley et al. 2005) methodologies are suitable for this species and have been used on the closely related Hector’s Dolphin (C. hectorii).
  • Use of set nets in inshore waters of the Western Cape and Northern Cape requires careful monitoring and management to determine levels of bycatch and, if necessary, the initiation of mitigation measures.
Research priorities: Most research on the species is, or has been, conducted or coordinated by members of the Mammal Research Institute of the University of Pretoria with research focussed on a number of topics, including distribution (Elwen et al. 2010), abundance and trends (Elwen et al. 2009b), foraging strategies (Elwen et al. 2009a, 2010; Leeney et al. 2011), ecological niche (stable isotope analysis), genetic population structure (Gopal 2014) and heavy metal analysis (Serot 2013). Research has also been conducted on vocalisation characteristics (Morisaka et al. 2011) and response to tagging attempts (Sakai et al. 2011). Specific research priorities include:
  • Density and abundance estimates along the entire range are needed to estimate total population size.
  • For a comprehensive picture of the population genetic structure, additional samples (biopsy/stranded) should be obtained from areas not sampled previously.
  • Estimates of dispersal rates and bycatch (including mapping geographical overlap with fisheries) are needed to evaluate their impacts on the population.
  • Studies of ecological niche and adaptability to different foraging environments are necessary to understand likely impacts of environmental 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, for example wwfsa.mobi, FishMS 0794998795.
  • Save electricity and fuel to mitigate CO2 emissions and hence rate of climate change.
  • Buy local products that have not been internationally shipped.
  • Reduce boat speed in high-density Heaviside’s Dolphin areas.
  • Report sightings on virtual museum platforms (for example, iSpot and MammalMAP) to help with mapping geographical distribution.

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,]
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