Heaviside`s Dolphin

We humans have always had a soft spot for dolphins – the graceful, energetic, intelligent ballerinas of the ocean. Look at how people react when dolphins suddenly surface before them in the surf. Smiles all around…  Dogs may be man's best friend on land, but in the ocean that title belongs to the dolphin. We know enough rescue stories to give this title credit. Dolphins save people from drowning and shark-attacks, but the other way around is also true: rescue stories of people pushing stranded dolphins back into the water or cutting pinching fishing line off the shiny blue-grey bodies. 

The "common" SA dolphin

The Heaviside dolphin

The Dusky dolphin

South Africa is very fortunate to have at least 12 dolphin species in our coastal waters. On the West Coast we have 3 species, the Common, Dusky and Heaviside's dolphin.  Water temperature and availability of food are probably the most important factors controlling or limiting the spread of small cetaceans (whales and dolphins).  As one might expected, these warm-blooded mammals are well adapted anatomically and physiologically to maintain and regulate their body temperature while living in a cooler medium that is highly conductive of heat.  Body heat is lost continuously to the environment, primarily through the body surface as well as in expired air, faeces and urine.  Passive heat loss from the body surface is greatly reduced by the insulative effects of blubber, a fat-filled fibrous tissue, beneath the skin.  Coping with seasonal changes in temperature also requires a flexible strategy.  Seasonal movements are a common strategy used by many dolphin species. 

The formation of schools by dolphins is a well known feature of their behaviour.  Undoubtedly, schools have multiple functions, including protection from predation and facilitation of learning processes in young animals, as well as enhancement of feeding opportunities and reproductive possibilities, such as gaining access to the opposite sex.  Species which form large schools feed predominantly on prey which itself forms schools or aggregations.  Dolphins feed almost exclusively on fish and cephalopods, especially squids and octopuses.  Crustaceans such as prawns and shrimps are eaten less frequently.

Hunting in schools is thought to be the most efficient means of exploiting food resources which are patchy or occur seasonally, because it reduces the chances of animals searching areas covered by others previously, and it also permits maximum utilization of prey patches when they are encountered.  Dolphins take turns to feed.  They leap synchronously from the water and are thought to look for signs of fish, such as fishing birds, while in the air.  This is very important as visibility underwater is restricted to 10-20m at best.  Leaping also enables them to surface and breathe without being slowed down by the turbulence of the surface.  They can reach speeds of up to 40km/h.  The ability to contain prey until each member has fed has obvious advantages and the use of cooperative herding behaviour appears to be widespread in several dolphin species.  

Movement at high speed means the navigation becomes critically important.  Dolphins navigate like bats, using ultra-sound, producing high-pitched sounds that bounce off obstacles ahead, allowing them to identify approaching objects and food with remarkable accuracy and speed.  The discovery of echolocation in dolphins stimulated the development of underwater listening and recording devices, used by submarines to detect submerged objects and by fishing boats to locate shoals of fish.

The West Coast of South Africa from Cape Point up to the south of Angola is home to an endemic, colourful, acrobatic little dolphin.  Although it is seen regularly from the promenade in Sea Point, seen in Table Bay by kayakers and sailors, by surfers in Big Bay and Elands Bay and fishermen in Port Nolloth, up until recently very little was known about these wonderful creatures. Even their name caused a lot of confusion.  Early in the 19th century a specimen was caught by Captain Haviside in the vicinity of the Cape of Good Hope and brought to the United Kingdom.  The zoologist John Edward Gray, who described the species in his Spicilegia Zoologica, misidentified Haviside as a surgeon of note named Heaviside and called the dolphin Cephalorhynchus Heavisidii or better known Heaviside's dolphin.  

The Heaviside's dolphin is a fairly small dolphin, growing to about 1.8m in length and weighing up to 75kg.  It loves the shallow waters of the coast and is seldom seen in waters deeper than 100m and is generally associated with the cold, northward-flowing Benguela Current.  Although they have been sighted in waters ranging from 9-19°C, most sightings indicate a preference of slightly cooler water between 9-15°C.  These dolphins are most commonly seen traveling in groups of 5-10, however at times they may temporary aggregate into larger pods.  The diet of Heaviside's dolphin consists mainly of juvenile hake, kingfish and gobies.  Other demersal fish, pelagic schooling fishes and cephalopods like octopus are also taken.

In general, Heaviside's dolphins appear to face fewer threats than other members of its genus.  Although fully protected legally, some killing with hand-thrown harpoons or guns has been reported.  Heaviside's dolphins are susceptible to entanglement in inshore gear such as beach seines, purse seines, trawls and gill-nets.  Concern has been expressed about the potential effects of pollution and boat traffic.

Because of the data scarcity surrounding these little dolphins, we do not know the number in which they do occur in our coastal waters and if their number has grown or fallen. If we look at the diminishing number of fish, and take into account  the fact that the dolphins have to compete  with humans, our nets and an ever-growing seal population, we can just assume their numbers must have fallen drastically and that maybe we now have only the last of the species left .

As custodians of our own little dolphin, it is critically important that we learn as much as we can as soon as possible about their numbers, the spreading, their habits and the threats to their existence so that we can assure that they will still play in our waters when the next generations arrive.