Laboratorio de Mamíferos
Marinos
Species
dusky dolphin - southern right whale - south american sea lion - south american fur seal
© Ilustration by Uku Gorter in Encyclopedia of Marine Mammals 3ra Edition
Southern Right Whale
Scientific name: Eubalaena australis
This species of whale lacks of dorsal fin. General body coloration is dark, normally black, but there are individuals with grey coloration, dark brown, or even white. A distinctive feature is the presence of several white patches, of varying size and shape, mainly on the ventral area; and occasionally on the dorsal area.
As all the baleen whales, blowhole is paired and V-shaped. It is placed dorsally, right behind the head. Due to shape and position of the blowhole, the resulting blow is V-shaped when seen from the front or from behind of the animal.
Females may reach a maximum of 17 meters (55 ft) in length, and male usually are not longer than 15.5 meters (50 ft). These animals may weight up to 40 to 50 tons. Calf at birth may be 4 to 5.5 meters (13 to 18 ft) long and weight between 1 and 3 tons.
The large head may represent up to 1/3 of the body length and have callosities. These callosities are thickenings of the skin present in the calf at birth. They are immediately colonized by a kind of amphipod crustacean named cyamids that are past from the mother. Shape, size and number of these callosities differ among individuals and they are employed to identify individuals during their whole life.
Southern right whale has a circumpolar distribution, between 20° and 60° in the South Atlantic, South Indian, and South Pacific oceans. Like most baleen whales, southern right whales are migratory. During austral spring they can be observed in reproductive activities in South America, Australis, New Zealand and other oceanic islands. Whales from the population on the Atlantic coast of South America move to feeding groups at mid and high latitudes of the Atlantic Ocean and the sub-Antarctic region. However, there might exist feeding grounds close to the edge of the continental shelf (shelf brake front), and even in fully oceanic areas. On the Argentinean coast they can be observed from northern Buenos Aires south to Tierra del Fuego and Falkland (Malvinas) Islands, reaching a maximum concentration during winter and spring at the reproductive area of Peninsula Valdés. In Argentina, this species shows a tendency to re-occupy distribution areas previous to commercial exploitation.
Population shows increasement since the 80’ in reproductive, feeding and migration areas. Recent studies showed that population increase rate in Península Valdés slightly decreased from nearly 7% in 2007 to 0.06% and 2.3% in 2016 for adults and calves, respectively. These changes could be related with whales moving from high to low density areas such as the gulfs San Matías and San Jorge.
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Map showing the worldwide distribution of southern right whale
Photograph of a southern right whale feeding. (Photo: Lucas Beltramino)
Southern right whales reach sexual maturity approximately at 6 years of age. The species reproductive cycle oscillates between 3 to 5 years with a gestation period of 12-13 months, a lactating period that may vary from 8 to 17 months, and an anestrus period (state of sexual inactivity in females during which they do not have estrogen cycles) of approximately 12 months. During mating, they generally form courtship and copulation groups including one female and several males. This promiscuous mating system is evidence of spermatic competence, the real competence is inside the female’s body among the various males’ sperm. The male that produces the greatest amount of sperm would have more chances to fertilize the only egg.
Southern right whales are filter feeders. They have a huge buccal cavity with 220 to 2600 pairs of rigid keratin plates known as baleens that hang on each side of the upper maxilla, leaving an opening at the front of the mouth. Baleens may reach over 2 meters long in an adult. External edge is smooth, and the inner one is covered of stiff fibers that interlock forming a net or filter where the food is retained.
Typical feeding behavior consist in swimming slowly with the mouth open (skimming), both at the surface and below it. This way, large volumes of water with food are introduced in the mouth through the front. After a filtering period, the whale closes its mouth pushing water and smaller organisms out, and food is retained in the inner filaments of the baleens. Their main prey includes juveniles and adults of euphausiids such as krill (Euphasia superba), large and mid-sized copepods, fish larvae and juveniles, and other zooplankton.
In the last years, there have been reports of population growth for southern right whales in the Southwestern Atlantic Ocean of 0.06% for adults and 2.3% for calves. Recently, there are records showing a trend to re-colonize distribution areas previous to commercial exploitation. Its conservation status is Least Concern (LC) given the current lack of direct treats.
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References
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