Garden Route

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MARINE MAMMALS

A distant splash and a spout of water vapour...

The Southern Cape region is an overlap of cold and warm sea currents and is a meeting place of marine mammals the world over. There is a great diversity of marine mammals that occur in South African waters (up to 40 species!). This includes the mammal that has ever existed; the blue whale (33m; 172 tonnes).

Like other mammals, whales and dolphins (Cetaceans) are air-breathers and must surface to breathe, expelling a spout of air and water vapour as they do so. They are warm-blooded, giving birth to live young, which they suckle. They can see both above and below the water surface by changing the lens shape of their eyes. A thick layer of fatty blubber serves as insulation. Highly specialised, whales and dolphins have lost or modified their limbs into flippers for stability and steering. Their horizontal tail-flukes provide propulsion. Both whales and dolphins jump out of the water, ‘breaching’, some whales slapping the surface with flippers and tail flukes.

Cetaceans form two groups: toothed, which eat mainly fish and squid; and those that have comb-like baleen plates that strain plankton.

Echolocation

Dolphins and toothed whales navigate and find food by producing high frequency, pulse ‘click’, which bounce back off solid objects. They communicate with each other using a variety of other sounds - groans, moans and whistles. Baleen whales, like humpbacks, produce low frequency ‘songs’ that travel for miles underwater.

These sounds are produced by the respiratory system, especially the nasal cavity, rather than vocal cords.
Underwater sonar used by many ships and submarines can interfere with the echolocation and communication channels of Cetaceans, making it difficult to find mates and locate feeding grounds.

Whaling

Large species, like the humpbacks, were once extensively hunted for their meat, oil and baleen, (used during the last century to make ‘whalebone’ stays for women’s corsets). which reduced their numbers severely. Whale hunting has fortunately been banned worldwide since 1986. Laws preventling boating within 300m of whales has led to a slow recovery in numbers.

Marine Protected Areas, such as Tsitsikamma National Park into which fishing boats cannot enter, provide a safe haven, where marine mammals can feed and give birth.

Marine Mammals that may be seen off the Southern Cape Coast:

Humpbacked Whale (14-15m)

Humpbacked whales are recognised by their long, narrow flippers, almost 1/3 of their body length. They have about 30 throat grooves and a small dorsal fin which is positioned far back. They vary in colour, some being completely white! The males sing complex melodies to communicate over long distance. Song themes are repeated for up to 20 minutes and change from year to year.

They are seen during their migration between breeding grounds off Mozambique and their summer feeding grounds in Antarctica (between June and December). They eat krill which they catch by circling beneath them while releasing a ‘curtain of bubbles’ to concentrate their prey.

Bryde’s Whale

The Bryde’s whale has three distinct longitudinal ridges that run from snout to near blow hole and 45 throat grooves that extend back to the naval. The dorsal fin is described to be very ‘shark-like’ (erected and hooked). They swim faster than the southern right whale, chasing shoals of small fish, such as anchovy, pilchard and squid. They do, however, also eat plankton. Some of these whales are resident off the South African coast all year, while others migrate to equatorial waters. They can often be seen 6-15km offshore, swimming in family groups of 5-6.

Southern Right Whale (14-17m)

The most common on the South African coast, these whales were known as the ‘right’ whales to hunt, because they move slowly and float when harpooned making them easy to bring ashore. Heavy exploitation in late 1800’s decimated more than 90% of their original numbers. Protection since 1935, has allowed their population to increase. Barnacles and whale-lice attach themselves to patches of raised rough skin on their heads.

Researchers use these to ID individuals. they are mostly seen between June and December, when females calve in sheltered, sandy-bottomed bays. For 3 months they remain in the warmer waters of the South African coast.

The calves drink ±200 litres of milk per day to build up blubber for the long trip to the Antarctic.

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