The spectacled porpoise (Phocoena dioptrica), is a small species rarely seen outside of its home territory in the waters of the Southern Ocean.
They are often referred to as shy and rarely bring attention to themselves when around humans.
Physical characteristics and Appearance
The spectacled porpoise is easy to identity due to its highly distinctive coloration.
The animal’s back is black, while its underside is white, creating two distinct zones of color that divide its body.
Its eyes are surrounded by dark rings resembling spectacles that give it its name.
The general outline of its body is similar to other porpoises, with a small head, no beak and a triangular dorsal fin, the latter larger in males than in females.
Males reach an adult length of about seven feet (2.2 meters) and females are somewhat smaller; adult weight ranges from 130 to 185 pounds.
The spectacled porpoise’s teeth are flat and spade-shaped, a feature shared with the other porpoise species and which distinguishes them from the dolphins.
They are fast swimmers and move quickly to avoid interaction with boats.
Diet and Hunting Methods
The diet of the spectacled porpoise is mostly a matter of speculation, since the species is so infrequently observed.
One dead specimen’s stomach contained anchovies and small crustaceans, a fairly typical diet for porpoises.
When hunting for prey the spectacled porpoise will use its hearing, eyesight and echolocation to help it locate and identify potential food sources.
Little is known regarding the hunted methods they use to actually capture their food.
Habitat and Migration
The spectacled porpoise has been observed throughout the northern reaches of the Southern Ocean and in coastal areas and islands of southern South America and New Zealand, including in estuaries and inland channels.
Whether coastal specimens and those found in the open sea represent the same or separate populations is unknown.
Numerous observations have been made of coastal specimens around the Tierra del Fuego at the tip of South America, for example, although it is generally believed that the deep waters of the open ocean are their primary habitat.
Migratory patterns are uncertain, although observers have only spotted the porpoise in cold waters and presumably they do not migrate out of temperate regions.
Social Structure and Communication
When navigating through the ocean these marine mammals often keep a low profile in order to avoid being noticed.
They may be seen swimming and rising to the surface slowly and silently barely disturbing the water as they move throughout their habitat.
When approached by boats or other human vessels they may quickly swim away to avoid contact.
While these marine mammals are fairly inconspicuous in the water they are capable of swimming at fast speeds when threatened or startled.
Most observations have indicated that the animal lives alone or in small groups of two or more.
In particular, females observed with infants were often seen with another adult.
Researchers have observed larger groups on occasion, but whether this is typical behavior is unknown.
Details about communication, courtship, social hierarchy and other elements of group dynamics among the spectacled porpoise remain unclear.
Breeding and Reproduction
Female spectacled porpoises give birth to their young (called calves) in the spring and summer.
Insufficient information exists regarding their gestation period, age of sexual maturity and lifespan.
Some estimates suggest a gestation period of 8 – 11 months with sexual maturity occurring when the porpoise reaches around 1.8 meters (5.9 ft.)
As with many cetacean species, the primary threat to the spectacled porpoise is human activity.
In the past they were hunted for food and bait for crabbing in Argentina and Chile, although the effects of these killings on the animal’s population in past decades is unknown.
Today, most are killed accidentally as a result of other fishing activity.
Gill nets, trawling and stranding due to the effects of fishing are believed to be the most common causes.
The expansion of fishing activity in the Southern Ocean, habitat disturbance due to oil extraction and mining and pollution from various sources are also considered potential threats.
Unfortunately, as with so much else about this interesting species, its total population and the actual impact of human activity on its numbers remain mostly unknown.