Heaviside's Dolphin

## Description

The Heaviside's dolphin is a small stocky cetacean native to the southwest coast of Africa. It has a distinct black, grey, and white body pattern, and is not easily confused with any other species in its range. The head and thorax are colored light grey with darker patches around the eye. The dorsal fin, fluke, and dorsal cape are a darker grey to bluish-black color with a band that extends from the dorsal fin to the blowhole. The underbelly is white, with bands that extend onto the lower rear of the body. Small white patches are located just behind the pectoral fins and a single white patch extends between these fins on the chest. In males, the white patch ends in a point, but in females widens out to cover the mammary slits. The head of the Heaviside's dolphin is cone-shaped with a blunt beak. The dorsal fin is triangular in shape and centered in the middle of the back.

## Distribution

Heaviside's dolphins range from Cape Point, South Africa along 2,500 km of coastline throughout Namibia and into Southern Angola. It is likely that the distribution of these dolphins in Angola is limited to the Benguela current's area of influence to the region, as they prefer temperate cool water. They mainly inhabit coastal waters, usually at depths less than 100 m, and sandy shores exposed to swell.

## Behavior

Heaviside's dolphins are energetic and social animals. They are attracted to boats and frequently bow-ride; they may also surf in coastal waves. They perform iconic vertical leaps and then re-enter water headfirst with almost no splash. Heaviside's dolphins usually occur in small groups of up to 10 and may form large aggregations of about 100 individuals or even more in high-density areas. In South Africa, these dolphins are active during the day and typically move offshore in the afternoon to feed on prey that raises to the surface at night. In the morning they rest and socialize inshore. However, in Walvis Bay, Namibia the dolphins typically stay inshore during the night. Heaviside's communicate with the help of high-frequency echolocation clicks and lower frequency and do not whistle. Low-frequency calls are produced most frequently in large groups engaging in social behavior. It is likely that the dolphins use these calls when socializing away from predator threat and switch to high-frequency clicks when foraging and traveling.

## Diet

Heaviside's dolphins are carnivores (piscivores). They feed on a wide variety of different fish, squid, and octopus.

## Reproduction

Heaviside's dolphins breed once every 2-4 years and their mating season is thought to occur year-round. The gestation period usually lasts 10 months and females produce a single calf. The young stay with their mothers for about 3 years and become reproductively mature between 5 and 9 years of age.

## Population

### Threats

Heaviside's dolphins are exposed to a variety of threats due to their limited range in coastal waters. These include bycatch and hunting, habitat degradation, pollution, climate change, and strikes with boats. The dolphins are also vulnerable to entanglement in inshore fishing gears such as beach seines, trawls, and gillnets.

### Number

There is no overall population estimate available for Heaviside's dolphin. However, abundance estimates from photographic mark-recapture studies are available at several locations in South Africa and Namibia. A three-year study between Cape Town and Lambert’s Bay, South Africa estimated 527 animals using 20 km of coastline in western Saint Helena Bay over six weeks of survey effort; 3,429 animals, using the 150 km of coastline around Saint Helena Bay, over three summer seasons; and 6,345 animals using the full ~390 km of coastline from Table Bay to Lambert’s Bay. Estimates are also available from two high-use areas in Namibia: Walvis Bay: 508 animals; and Lüderitz: 494 animals. Currently, the Heaviside's dolphin is classified as Near Threatened (NT) on the IUCN Red List.