Red List of South African Species

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Vulnerable (VU)
Assessors: Simon Elwen Ken Findlay Mike Meyer Herman Oosthuizen Stephanie Plön
Contributors: Claire Relton
Reviewers: Matthew Child

Rationale

Although the population is recovering, commercial whaling in the Antarctic within the last three generations (82 years) reduced the global abundance of species significantly. As commercial whaling has ceased, the species is evaluated under the A1 criterion. Model results revealed a 6% probability for Endangered, a 54% probability of Vulnerable, and a 40% probability of Near Threatened. Thus, the species is listed as Vulnerable A1d based on historical decline in line with the global assessment. Circumpolar surveys estimate around 8,300 mature males, which is extrapolated to around 40,000 individuals in total. Within the assessment region, the historical depletion may have created a skewed sex ratio, which may make this species more vulnerable to minor threats. For example, systematic surveys from the Antarctic showed no significant population increase between 1978 and 1992. Recent modelling results corroborate the Sperm Whale’s slow recovery rate, where a small decrease in adult female survivorship could lead to a declining population. Ongoing loss of mature individuals from entanglement in fishing nets and plastic ingestion could be hindering population recovery in certain areas. Furthermore, marine noise pollution may be an emerging threat that could suppress population recovery, but results are ambiguous. The effects should continue to be monitored. Overall, the overexploitation of Sperm Whales has ceased and they usually remain fairly far from anthropogenic effects due to their deep sea distribution, and the large-scale commercial fishing industry does not target major Sperm Whale food sources. However, given their historical depletion, their slow growth rate (possibly only 1% per year) and their modelled sensitivity to disturbance, current abundance and population trend estimates are urgently needed and this species should be reassessed once such data are available.

Regional population effects: Sperm Whales are highly migratory and wide-ranging. There are no barriers to dispersal, thus rescue effects are possible.

Distribution

Sperm Whales have a broad geographic range (Rice 1989), and may be present in nearly every marine region from the tropics to high latitudes. Typically they are located in deeper waters or along the continental slope, avoiding waters shallower than 300 m. Their geographic range also includes a number of enclosed or partially enclosed areas, including both the Mediterranean and Baltic Seas, the Sea of Okhotsk and the Gulf of Mexico. Their distributions vary according to sex and size, where males have been observed closer to inshore areas than females (Best 1999). Additionally, females and their young are often restricted in their range to regions between 40°N and 40°S, while males may migrate as far as 70°N and 70°S in summer, and larger males appear to extend further north or south than smaller individuals. Sperm Whales are known to travel substantial distances, with one individual reported to have covered a straight-line distance of  7,400 km (Ivashin 1967). Although some overlap in geographic distribution is known to occur between northern and southern hemisphere stocks, populations are thought to be genetically isolated because seasonal breeding periods occur six months apart.

The International Whaling Commission (IWC) recognises nine Sperm Whale divisions for the southern hemisphere, which have been based more specifically on data available from commercial whaling, rather than actual biological factors (Donovan 1991). Although Sperm Whales migrate long distances, and exhibit low genetic differentiation between ocean basins (Lyrholm et al. 1999; Mesnick et al. 1999; Drouot et al. 2004a), some studies infer a high degree of geographic structure among populations across many regions (Bannister & Mitchell 1980; Kasuya & Miyashita 1988; Rendell & Whitehead 2003; Whitehead 2003). This is corroborated by recent molecular analyses that suggest females show site fidelity to coastal basins while males disperse widely for breeding (Engelhaupt et al. 2009). Within South African waters, Sperm Whales are present across the majority of the Exclusive Economic Zone (EEZ), frequently in deep waters off the west coast, and excluding shallow regions along the continental shelf. Records from Durban (30°S) and Donkergat (33°S) found that males and females reveal varied seasonality where large males were often caught in this region in spring, while juvenile males and females were more frequently caught earlier in winter

Population trend

Trend

Using historical trajectories, an abundance model for global Sperm Whale populations was developed to estimate the population decline between 1700 and 1999 (Whitehead 2002). This model includes only the threat of legal commercial whaling and does not consider any other anthropogenic threats to this species, such as ship strikes, illegal whaling in the North Pacific and Antarctica, climate change, pollution, entanglement in fishing gear, or the persistent effects of social disruption and sexually skewed population structure. These factors may limit population recovery in many areas. This model postulates that Sperm Whale populations have shown a substantial recovery since commercial whaling of this species was largely prohibited, but may, in fact, be an overestimation of current Sperm Whale recovery trends. On the other hand, some factors (such as the use of a relatively low rate of population increase) suggest that this model may result in an underestimation of population abundance. However, despite these uncertainties, this model remains the most accurate means of estimating recent population trends. The estimated global pre- exploitation population of 1.1 million Sperm Whales is thought to have declined by 29% by 1880 due to “open-boat” whaling operations, and then by 67% of the original population (to around 361,000) by the 1990s as a direct result of modern whaling (Whitehead 2002). Their global population in 1999 (10 years after the end of commercial whaling) was estimated at 32% (95% CI: 19–62%) of its original abundance, thus at approximately 352,000 individuals. Following the trajectory (used in Whitehead 2002), the model was modified slightly to extend the endpoint to 2003 (Taylor et al. 2008). This produced a population estimate in 2003 of 44% of the 1921 population. Indeed, of 1,000 model runs, 6% gave populations in 2003 of < 30% of that in 1922, 54% gave a 2003 population between 30–50% of that in 1992, and  0% suggested depletion levels of less than 50% over this time (Taylor et al. 2008). Thus, the species remains Vulnerable under the A1 criterion.

Two major global Sperm whaling operations were driven by the high commercial value attached to this species: the primitive “open-boat” hunt from 1712–1920 (Best 1983), and the modern whaling expeditions from 1910–1988 (Tønnessen & Johnsen 1982). Modern whaling operations did not, however, impact all Sperm Whale populations. For example, populations in the western North Atlantic remain at reasonably high densities, and show evidence of successful reproduction (Gordon et al. 1998). After the decline of other large rorqual species and the invention of new uses for Sperm Whale oil, commercial whaling of this species was intensified until 1964, when an annual peak of 29,255 individuals were caught. Limits imposed by the IWC after 1968 coincided with the development of synthetic alternatives for Sperm Whale oil, resulting in a decline in Sperm whaling efforts. Commercial Sperm whaling is currently prohibited by the IWC. Under special permit, only one Sperm Whale was recorded as caught in the 2009/10 season by a Japanese whaling vessel in the North Pacific (IWC unpubl. data). Although, the effect on the Sperm Whale stocks by small-scale recent operations is negligible, the value of these activities is severely questioned.

There is some concern that a few populations are still in decline, and there is no clear quantitative evidence suggesting that the global population has shown a recovery since large-scale whaling ceased in 1980 (Taylor et al. 2008). However, there is also no evidence to the contrary. Future population assessments are required to address the doubt surrounding the recovery of this species. Within the assessment region, we assume that the population is at the depleted level suggested by the global assessment, although evidence from the circumpolar surveys indicates that the population is recovering (IWC unpubl. data). However, the historical depletion may have created a skewed sex ratio, which may make this species more vulnerable to minor threats (for example, plastic pollution, ship strikes, entanglements). As such, while the Antarctic population should have repopulated from less heavily exploited breeding populations at lower latitudes following the end of large-scale commercial whaling (Taylor et al. 2008), systematic surveys of Sperm Whales in the Antarctic showed no substantial or statistically significant increase between 1978 and 1992 (Branch & Butterworth 2001). As such, we infer the population trend to be stable but current surveys are required to assess current population trends. Corroborating the empirically estimated slow  recovery rate, a recent population model revealed that Sperm Whale populations grow slowly and are potentially sensitive to survivorship rates of adult females, where a slight decline in survivorship could lead to a declining population (Chiquet et al. 2013).

Threats

Commercial whaling, historically the most substantial threat to the livelihood of this species, has ceased. Nonetheless, a range of additional factors threaten the remaining diminished populations of Sperm Whales. Considering that Sperm Whales are a large-scale migrating species, threats affecting this species in other areas of the world may impact populations that frequent the waters around South Africa, particularly those in the Atlantic, Indian and Southern Oceans. Similarly, population recovery is hindered by slow growth rates, possibly c. 1% per year (Whitehead 2002).

Similar to other cetaceans, Sperm Whales are vulnerable to entanglement in fishing gear, specifically gillnets, across a range of areas. This is particularly problematic in the Mediterranean Sea where Sperm Whales were one of the most commonly recorded non-target species caught in driftnets (Northridge 1991) before they were banned in 1990. Since 1990, illegal driftnet fisheries still occur in the Mediterranean but the frequency of Sperm Whale entanglements has declined considerably (Drouot et al. 2004b). Other cases of Sperm Whale entanglements have been recorded in Ecuador (Haase & Félix 1994) and California (Barlow & Cameron 2003), but are also considered to be a minor threat to this species within the assessment region. Although occasional catches in small scale gillnet fisheries are not currently expected to have a large effect on the global population, it is likely there are many more cases of Sperm Whale entanglements in unregulated driftnet fisheries in deeper waters, which are not recorded.

Occasionally, Sperm Whales engage in an activity known as “depredation”, when they actively remove fish from fishing gear (most commonly from demersal long-lines). This appears to be an increasing and risky phenomenon, which may result in entanglements, injury, death (HuckeGaete et al. 2004), and hostility from fishermen (including shooting of Sperm Whales) (Donoghue et al. 2003). It has been documented in a number of marine regions across the globe, including the North Atlantic, Chile, southeast Alaska, South Georgia, as well as other Southern Ocean islands and waters within the assessment region (Meÿer et al. 2011). In the Prince Edwards Islands (south of South Africa), Sperm Whales have been known to remove Patagonian Toothfish (Dissostichus eleginoides) from longline fishing vessels, which occasionally results in the illegal use of dynamite or thunder flashes to deter Sperm Whales (Ashford et al. 1996; Kock et al. 2006).

The sensitivity of Sperm Whales to noise is largely unconfirmed, where studies have shown contrasting evidence of high sensitivities (Watkins et al. 1985; Bowles et al. 1994) versus little to no effects on the species (Madsen & Møhl 2000; Madsen et al. 2002). There is a lack of research investigating the long-term effects of noise, sonar and seismic surveys on Sperm Whales, and, as yet, no mortality has been observed as a result of these disturbances. On the other hand, this possible threat is increasing globally and thus the sensitivity of Sperm Whales to noise should be treated with caution.

Sexually-skewed whaling efforts may have long lasting effects on the reproductive rates (Whitehead 2003) and complex social cohesion of certain stocks, including those of the assessment region (Best 1979; Clarke et al. 1980; Whitehead et al. 1997); however, over time this inequality is likely to correct itself automatically. The population recovery and growth of Sperm Whales is fairly low, in fact, the maximum rate of increase is predicted to be around 1% per annum (Whitehead 2002). Population recovery since the end of commercial whaling, although inferred, remains purely theoretical for this species. Additionally, the severely depleted population of large, mature whales in the high latitudes of the Antarctic was assumed to have recovered from lower latitude areas where Sperm Whales were less heavily exploited following the end of  commercial whaling. Contrastingly though, systematic surveys conducted for this species in the Antarctic did not reveal any significant increase between 1978 and 1992 (Branch & Butterworth 2001).

Collisions with ships impact Sperm Whales at a more regional scale, and have been specifically documented off the Canary Islands (André & Potter 2000) and in the Mediterranean (Pesante et al. 2002). Sperm Whales were listed as the most affected species by ship strikes near the island of Tenerife (Canary Islands), representing 48.8% of the total collision cases.

The ingestion of marine debris, particularly plastic, is also known to be an increasing threat to this species (Viale et al. 1992; Simmonds 2011; de Stephanis et al. 2013). In 2008, the stomachs of two Sperm Whales stranded on the coast of California were found to contain substantial quantities of plastic debris, fishing net scraps and rope (Jacobsen et al. 2010). Gastric impaction as a result of this ingested debris was the most probable cause of death for both individuals (Jacobsen et al. 2010). Walker and Coe (1990) found that Sperm Whales are primarily affected by problems associated with the ingestion of marine debris, and this may cause a specific threat within the assessment region. Sperm Whale tissues also have high levels of some contaminants (O’Shea 1999; Nielsen et al. 2000), but it is uncertain whether this has an effect on the population level.

Uses and trade

Extensive commercial Sperm whaling has ceased, however, small-scale hunting for Sperm Whales continues in Japan and Indonesia. Under the IWC’s Special Permit, 10 individuals are taken per annum by Japanese whaling fleets (Clapham et al. 2003)

Conservation

The major historic threat to Sperm Whales (commercial whaling) has largely ceased. Thus, this species seems relatively secure from this threat in the short and medium term. Sperm Whales largely avoid anthropogenic effects, as they are mostly located in deeper waters away from the coastline. Additionally, much of this species’ food resources are safe from overexploitation by humans, as they feed predominantly on deep-water squid and fish in mesopelagic and benthic-pelagic habitats (Clarke 1977). This species is also listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and Appendices I and II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).

In order to reduce ship strikes, determining the distribution and population estimations of Sperm Whales in areas of high vessel traffic is required. Additionally, high speed vessels may require dedicated on-board observers in order to detect the presence of Sperm Whales and other cetaceans along the trajectory of the vessel. Finally, detailed on-board monitoring reports of cetacean collisions are essential to assess the severity of this threat to cetacean populations within the assessment region.

There have been a number of legislative interventions to limit marine pollution. A key intervention is the 1978 Protocol to the International Convention for the Prevention of Pollution from Ships (MARPOL), which acknowledges that ships add a significant and manageable quantity of pollution into marine environments (Lentz 1987). Annex V of MARPOL aims to “restrict at sea discharge of garbage and bans at sea disposal of plastics and other synthetic materials such as ropes, fishing nets, and plastic garbage bags with limited exceptions”. Nevertheless, this legislation is largely ignored and Clarke (1977) estimated that 6.5 million tons of plastic is discarded into the ocean each year. Enforcement and international cooperation is essential to ensure that all marine vessels comply with the Annex V policy.

Education and community involvement is also a powerful tool with which to approach the threat of marine (particularly plastic) pollution. Considering that land-based pollution usually ends up in the ocean, awareness, education and terrestrial-based action is often more effective in mitigating the problem compared to the development of addition legislative policies (for example, Ross & Swanson 1994). 

Recommendations for managers and practitioners:
  • Systematic monitoring: design and implement a monitoring programme (acoustic and sightings) that can detect population size and trends. For example, by using the recently developed single nucleotide polymorphism markers (Morin et al. 2007).
  • Develop best practice guidelines for seismic surveys and enforce regulations.
Research priorities:
  • Population size and trends. Given the long and deep diving behaviour of male Sperm Whales, the global estimate is almost certain to be an underestimate, as it is based on a sighting survey.
  • Effects of marine noise pollution on Sperm Whale populations.
  • Understanding the effects of minor threats (pollution, ship strikes, entanglements etc.) to this species, as well as the rates and trends associated with population recovery.
Encouraged citizen actions:
  • Whale-watching operators could contribute to photoID catalogues and behavioural observations.
  • Report strandings to relevant authorities.
  • Participate as volunteers in Sperm Whale research projects.
  • Avoid using plastic bags, participate in beach and river clean-up initiatives, and raise awareness of the environmental threats associated with marine and terrestrial litter.
  

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,]
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