BRYDE'S WHALE

(Balaenoptera edeni)

Appearance
Bryde's whales occur in tropical and sub-tropical latitudes in the Indian Ocean and can be seen anywhere along the south-eastern Cape coast. But as with most baleen whales, the best sites are capes or promontories, such as Robberg. This is especially so during autumn and early winter, when shoals of small fish are plentiful inshore and are easily spotted by the diving gannets associated with them. When seen at sea, Bryde's whales are difficult to tell apart from some other rorquals, such as Minke and Sei whales. But, they are most likely to be confused with Minke whales, because both have prominent dorsal fins. Minke and Bryde's whales can also be distinguished by their feeding patterns. Minke whales swim rapidly at the surface, on the perimeter of fish shoals, taking fish on the outside of the shoal.

In contrast, Bryde's whales can be seen lunging up through shoals, sometimes exposing the whole head with the mouth massively distended and scattering any penguins and gannets in the way. The upper body of Bryde's whales is dark grey and often has a 'blotched' appearance. In relation to the body, the dorsal fin of Bryde's whales is large and upright, making them look more like huge dolphins than whales.


Behaviour & Feeding
Little is known of the biology of Bryde's whales. Off the south-eastern Cape coast there appear to be two populations or stocks. One is seemingly 'resident' (non-migratory) in inshore, shallow waters, where shoals of small fish are likely to be abundant. The second appears to be an offshore stock, possibly undertaking seasonal migrations and occurring here only in spring and summer. Although Bryde's whales from elsewhere are known to feed on small crustaceans (euphausiids) and small shoaling fish, the inshore 'resident' stock apparently feed exclusively on small shoaling fish, mostly pilchards, anchovies and maasbanker. Bryde's whales are usually seen singly, although small groups may form during feeding. They are not particularly fast swimmers, attaining speeds similar to humpback and Minke whales, but they can move rapidly when disturbed. Equally, they are not deep divers, usually spending no more than about two minutes underwater, although dives as long as four minutes have been recorded.


Reproduction
In the North Pacific, Bryde’s whales have a definite breeding season. Little is known of the reproductive cycle of Bryde's whales in South African waters, though the 'resident' stock presumably mates and gives birth in autumn and winter, because more calves are seen at this time. After a gestation period of about one year, females give birth to a single calf of about 4 m, that is suckled during the following year, before she once again falls pregnant.

Threats
None known. Whaling for this species was generally only on a small scale and no populations are known to have suffered serious depletion.

Conservation status
Insufficiently known - although it is suspected that the resident stock of this species may be Endangered, Vulnerable or Rare, there is insufficient information available to place it any of these categories.


Gwen Penry is a Ph.D. student with the CDS and is currently researching the population biology of Bryde's whales. Contact her research@dolphinstudies.co.za to find out more about her research and if you can help.