The black dolphin is the least known of the genus Cephalorhynchus,
with almost nothing known about the biology or natural history,
no records of specimens held in captivity, and almost no formal
studies of the species. It appears to be mostly typical of
the genus, consuming similar prey, making similar vocalizations,
and having the same inherent wariness, which helps to result
in its obscurity.
The black dolphin is found only in Chilean waters between
Valparaiso (about 30° S.) and s. Isla Navarine, just north
of Cape Horn, (55°. S.). The most easterly sighting was
in the Strat of Magellan, just east of First Narrows (52°
30' S., 60°. 20' W.). It is possible that its range extends
south to Cape Horn (around 56° S.). There is very little
overlap between the range of the black dolphin and that of
the Commerson's dolphin, but they have been seen together
in the Strait of Magellan, the Beagle Channel, and Cape Horn.
The records are from the edges of their respective ranges.
The distribution is more or less continuous within its range;
there are no significant gaps that isolate different groups.
The black dolphin in many ways resembles the Heaviside's
dolphin, with a small adult size of around 1.4 meters, a low,
rounded dorsal fin, and dark coloration. It has a white throat
and belly, a white spot behind the flipper, and a dark line
on the sides running from the cranial to the caudal end. When
in the water, it is described as tan, brown, lead-colored,
or gray. Out of the water, it is found to be nearly black
on most parts and pure white on other parts. After death,
the color darkens quickly, especially if the specimen is left
in the sun. Its resemblance to various species of the family
Phocoena probably represents parallel development as the species
occupy similar ecological niches. Cetacean litterature includes
many inaccurate descriptions of this species.
Very little is known about the black dolphin's behaviour.
It is generally not blatant or aggressive, and does not breach
often. Individuals are often seen with groups of feeding sea
birds. The northern stock is far more gregarious than the
southern stock. While in the southern part of the range, individuals
are wary of boats and very difficult to approach, those in
the northern areas do occasionally approach boats and bow
ride. In addition, groups in the north are much larger, sometimes
reaching as many as 4,000 individuals.