By whale biologist Katja Vinding, PhD Student, University of Pretoria.

 

 

De Hoop is a unique place to observe the southern right whale (Eubalena australis). Every year from June to December the southern right whales spend time at the South African coast, where they either give birth and nurture their calves or engage in mating and social behaviour. De Hoop is one of the most important places along the South African coastline for the southern right whales, they arrive in June, reach a peak in September and leave by December/ January (Best and Scott 1993). The region from St. Sebastian Bay to De Hoop is regarded as the most important nursery area for right whales on the South African. This region of the Cape Infanta represented 70-80% of the cow-calf pairs observed on the entire South African coast between 1981 and 1986 (Best and Scott 1993). This particular 71 km stretch of coastline ranks as the most important nursery area for right whales worldwide.

 

The southern right whale prefers the shallow and protected bay areas of coastal waters (Elwen and Best 2004a, Elwen and Best 2004b). Above all, De Hoop is an important calving and nursing area. The pregnant females return to the South African shores from the month of June. De proportions of sightings of calves has been calculated (Best and Scott 1993) and at De Hoop the sightings of calves increase from zero in June to 15-22% in August, September and October (reflecting the season of births). In November most of the sightings are mothers with calves (33%) and in December 42% of the animals are mothers with calves, reflecting the earlier departure of animals without calves (Best and Scott 1993). From December they return to the Arctic region, where they feed. It is not unusual for a few mother and calf pairs to be seen until the beginning of January –these are thought to be late-born calves. From helicopter surveys conducted at De Hoop (during October), it has been found that the animal densities are highest at De Hoop at Koppie Allen and Klipkoppie (Best and Scott 1993), making them the best whale spotting sites at De Hoop. Southern right whales seem to follow a pattern where they move westward during the season, starting at De Hoop. From satellite tagged animals we know that the main movement along the south coast is following a westerly direction with cow-calf pairs moving slowest (Mate et al. 2011).

 

Generally the females with calves stay closest to shore, less than 900m (Best 1990) and try their best to avoid the so-called Surface Active Groups (SAG, related to mating). These groups normally consist of one female and several males. The activity in SAGs is high and it can potentially be dangerous for a mother with a calf to get close to an SAG if the calf gets separated from the mother (Elwen and Best 2004). Therefore you will see mothers with calves keeping a safe distance from SAGs and even from other mothers with calves. Later in the season the mothers will let calves socialize for a short while. But, if you are flying over the area you will see the mothers with calves spread out like a mosaic, where they are close but not too close to each other.

Most mature females follow a 3-year cycle. They mate during the first season, give birth and nurse their calf the following season, and in the third season take a year of rest. However, some whales follow a 2 or 4-year cycle (Best 1994). This "synchronization" of seasons is probably a reflection of the relatively restricted calving season in the species (95,5% of calves are born within an estimated 118 days, peaking in late August (Best 1994)).  As with all whales, southern right whales always give birth to one calf at the time. It is a lot of investment to nurture a calf and the mother does not feed while she is at the South African coasts. Calves are about 5-6 m at birth and weigh about a ton.

Southern right whales are distributed in the southern hemisphere generally between 20°S and 60°S (Mate et al. 2011). They migrate between the wintering feeding grounds across a broad latitudinal range between about 32°S and 65°S, with the main feeding areas thought to occur between 40°S and 55°S and calving/mating grounds in the near shore waters of the southern coastlines of South Africa, Argentina, and Australia between 20°S and 45°S (IWC 2001). Smaller numbers of whales are found around oceanic islands including the New Zealand sub-Antarctic Auckland and Campbell Islands and around Tristan da Cunha and Gough Island in the South Atlantic (IWC 2001).

During the satellite study by Mate et al (Mate et al. 2011), five of the tagged southern right whales left the South African coast while their tags were still transmitting. They travelled between 3.800km – 8.200km over 53-110 days before the transmitters stopped sending. While migrating the net speed ranged from 2.8 – 3.8 km/h (mean 3.3 km/h). The net speed of animals while at the shores were 1.0 – 2. 8 km/h (mean 1.6 km/h). Mothers with calves close to the shores were found to have a net speed of 0.6 – 1.5 km/h (mean 1.1 km/h) (Mate et al. 2011).

 

 

The right whales received their name because they were thought to be the right whale to catch! Because of its thick layer of blubber, it will stay afloat when dead, which was a big advantage when the whales were hunted. The southern right whale was the first of the large whales to be protected. The International Whaling Commission (IWC) banned commercial hunting of southern right whales in 1935 and it has also been protected in South Africa since then. Accordingly the southern right whale has been internationally protected from commercial hunting since 1935 apart from illegal hunting (IWC homepage). Since then the IWC has designated a right whale protection stock which sets the catch to zero (illegal hunting was probably high).

The population was severely depleted in the pre-20th century. The global estimate of the population was 70,000-100,000 pre-hunting.

The last estimate of the southern right whale population, conducted in 1997, was 7,500 globally (IWC 2001). The population is estimated to increase by 7% a year, so if the population follows this pattern, it should be above 16,000 globally by now.

The South African population was estimated by Peter Best to be 3,400 in 2001. The South African population is the largest of the three main populations.

The 7% annual increase is at a maximum biological rate of increase across a wide proportion of its known range (IWC 2001).

Even though it is a success story, the population is still not at the same number as pre-exploitation abundance. It is about 10% of that. The fitness of an over-exploited population is at risk due to genetic loss (the gene pool is reduced) which makes the population more vulnerable to diseases.

In 1996, the International Union for Conservation of Nature and Natural Resources (IUCN 2013) listed the southern right whale in the category “least concern”.

 

 

 

Various dolphin species are found in the coastal waters of De Hoop, including the Indo-Pacific hump-backed dolphin (Sousa chinensis plombea form). They are usually found along the coast where they frequent the shallows or inshore waters. They tend to prefer areas with open river mouths and have mainly been observed feeding in such areas. They are rarely found in waters deeper than 20 meters, placing them in frequent contact with human activities.  Incidental mortality in fishing gear and degradation and loss of habitat are the greatest threats to this species throughout its range. This species is listed as “Near Threatened” (IUCN).

The bottlenose dolphin (Tursiops truncatus; “Least Concern” (IUCN)) and the Indo-Pacific bottlenose dolphin (Tursiops aduncus,” Data Deficient” (IUCN)). The common bottlenose dolphin is larger than the Indo-pacific bottlenose dolphin and it occurs generally offshore except in Namibia where it is inshore. Tursiops aduncus are distinguished from common bottlenose dolphins by their longer beak and more uniform coloration on the dorsal and some adults possess freckled dark spots on the abdomen. Tursiops aduncus, which is recognized as a separate species, is found inshore on the east of Cape Town and throughout the Indian Ocean as well as into the South West Pacific (Best 2007). This coastal distribution (rarely found in waters deeper than 30 meters) results in frequent contact with human activities. This makes them particularly vulnerable to the alteration or loss of their habitat and to direct injury by vessels.

Another dolphin species that is often spotted around De Hoop is the long-beaked common dolphin (Delphinus delphis). With an IUCN listing as “Data Deficient” (IUCN) it is not possible to determine their population trend.

The humpback whale (Megaptera novaengliae; “Near Threatened” (IUCN)) could be observed during the winter period, when they migrate through the area on their route to Mozambique. The Bryde’s whale (Balaenoptera brydei) is also frequently observed in the area.

 

Major threats for cetacean species are entanglements in fishing gear and collisions with shipping (Meÿer et al. 2011), which is one of the reasons why Marine Protected Areas are crucial. A full review of previous cetacean studies and current knowledge are available from (Elwen et al. 2011).

 

 

Literature 

Best, P. B. 1990. Trends in the inshore right whale population off South Africa, 1969-1987. Marine Mammal Science 6:93-108.

Best, P. B. 1994. Seasonality of reproduction and the length of gestation in southern right whales Eubalaena australis. Journal of Zoology (London) 232:175-189.

Best, P. B. 2007. Whales and dolphins of the Southern African sub-region. Cambridge University press.

Best, P. B. and Scott, H. A. 1993. The distribution, seasonality and trends in abundance of southern right whales Eubalaena australis off De Hoop Nature Reserve, South Africa. South African Journal of Maine Science 13:175-186.

Elwen, S. H. and Best, P. B. 2004. Female southern right whales Eubalanena australis: Are there reproductive benefits associated with their coastal distribution off South Africa? Marine Ecology-Progress Series 269:289-295.

Elwen, S. H. and Best, P. B. 2004a. Environmental factors influencing the distribution of southern right whales (Eubalaena australis) on the south coast of South Africa I: Broad scale patterns. Marine Mammal Science 20:567-582.

Elwen, S. H. and Best, P. B. 2004b. Environmental factors influencing the distribution of southern right whales (Eubalaena australis) on the south coast of South Africa II: Within bay distribution. Marine Mammal Science 20:583-601.

Elwen, S. H., Findlay, K. P., Kiszka, J., and Weir, C. R. 2011. Cetacean research in the southern African subregion: a review of previous studies and current knowledge. African Journal of Marine Science 33:469-493.

IUCN, R. L. o. T. S. 2013. Southern Right Whale (Eubalaena australis). http://www.iucnredlist.org/details/8153/0 The International Union for Conservation of Nature and Natural Resources.

 IWC, I. W. C. 2001. Report of the workshop on the comprehensive assessment of right whales: a worldwide comparison. Journal of Cetcaean Research and Management 2:1-60.

Mate, B. R., Best, P. B., Lagerquist, B. A., and Winsor, M. H. 2011. Coastal, offshore, and migratory movements of South African right whales revealed by satellite telemetry. Marine Mammal Science 27:455-476.

Meÿer, M. A., Best, P. B., Anderson-Reade, M. D., Cliff, G., Dudley, S. F. J., and Kirkman, S. P. 2011. Trends and interventions in large whale entanglement along the South African coast. African Journal of Marine Science 33:429-439.