Burmeister's porpoise (scientific name: Phocoena spinipinnis) is one of six species of marine mammal in the family Phocoenidae. The other five are the Finless porpoise, the Spectacled porpoise, the Harbour porpoise, the Gulf of California harbor porpoise, and Dall's porpoise.
|Burmeister's porpoise. Source: Michigab Science Art|
|Size comparison of an average human against the Burmeister's porpoise. Source: Chris Huh|
A cetacean, Burmeister's Porpoise was discovered by zoologist Hermann Karl Konrad Burmeister of Cologne when he noticed that the dorsal fin of this porpoise extended into an exceptionally sharp point. The dorsal fin also contains rows of tubercles along its front edge, providing the basis for its scientific name spinipinnis (which is derived from the latin words spina = thorn and pina = fin).
The body ranges from 1.4 to 1.8 meters in length, making it one of the smaller species in this family. Males appear to be slightly larger on average than females. Burmeister's porpoise is a uniform color dorsally varying from dark grey to black while the ventral side is paler in pigmentation. This species's tendency to turn black soon after death has earned it the nickname the black porpoise.
The presence of an eye patch surrounded by a pale grey ring is a useful identifying characteristic. Additionally, a unique characteristic is the presence of asymmetric flipper stripes with a nearly uniform, straight edged shape on the left side and a more curvacious right side patch that gradually narrows anteriorly.
The skull morphology of Phocoena spinipinnis can be described based on other members of the genus, particulary the Harbour porpoise (Phocoena phocoena) whom it closely resembles, with the following characteristics: a brain case tending to be much more compact lengthwise, a dorsal profile of the supraoccipital bone in line with the dorsal profile of the rostrum instead of at a 20 degree angle, a larger temporal fossa, and a lower tooth count of 14-16 upper teeth and 17-19 lower teeth on each side.
Other Physical Features: Endothermic; Bilateral symmetry
Burmeister's porpoises are one of the most poorly known species of this family. They travel in small groups, and it is rare to find more than eight individuals together at one time.
They swim in quick, jerky movements, yet are very inconspicuous swimmers, barely breaking the surface of the water when they come up to breath and seldom seen breaching. During surfacing, they break the surface about seven to eight times. This is followed by an underwater dive lasting up to three minutes and a reappearance as far as fifty feet away. The fastest recorded speed for this species is four kilometres per hour.
Burmeister's porpoises are very timid and scatter rapidly when approached by boats. These animals are very difficult to find in rough waters and windy conditions, which may be a reason why there are so few spottings of this species. Vital statistics are not well documented but one calf was found to have a respiration frequency of seven breaths/min in a stressed situation. No underwater sounds have been recorded for this species, yet the species can be identified on the surface by respiration sounds.
Key Behaviors: natatorial; motile; social
At an average length of 154.8 and 159.9 centimetres respectively, male and female Burmeister porpoises reach sexual maturity. Reproduction has not been extensively studied in this species; however, a pregnant female with a near term fetus was found off the coast of Uruguay in late February. This observation along with other collected specimens have lead reasearchers to believe that the reproductive season occurs during the same period throughout this family with mating from June to September, calving in May through August, and gestation lasting about 10 months. At birth, calves generally have a length of at least 44 cm.
Key Reproductive Features: Iteroparous; Seasonal breeding; Gonochoric/gonochoristic/dioecious (sexes separate); Sexual; Viviparous
Distribution and Movements
Burmeister's porpoises are only found along the coastal waters of South America. They inhabit the Atlantic waters on the coast of Brazil and continue to be found south around the coastlines of Tierra del Fuego and the Falkland Islands and north into the coastal Pacific waters of Peru.
Burmeister's porpoises usually inhabit shallow waters of 150 meters or less in depth and can often be seen in rivers and estuaries. Because the Atlantic Ocean has a wider continential shelf than the Pacific, it might provide a more preferred habitat. However, the Pacific coast population is larger. This discrepancy may exist because the Burmeister's porpoises must compete with other more dominant coastal cetaceans on the Atlantic Coast, including the Tucuxi dolphin (Sotalia fluviatilis) and Franciscana (Pontoporia blainvillei). In contrast, Burmeister's porpoises are successful on the eastern Pacific coast, where they are the chief cetacean species in this area.
The Burmeister's porpoise feeds primarily on anchovies and hake, yet squid, euphasiids, mysid shrimp, and up to nine species of fish also have been found to be a part of its diet; in addition other aquatic crustaceans are elements of this cetacean's diet. Those found off the coast of Chile have been known to eat molluscs as well.
Economic Importance for Humans
Phocoena spinipinnis is often used for its meat in areas where this species is frequently caught in fishing nets. The meat of these individuals is used either as food for humans or for baiting crab traps.
Threats and Conservation Status
Like many other cetaceans, the Burmeister's porpoise is often taken as bycatch in fishing nets. Van Waerebeek et al. studied the number of cetaceans caught by fisheries at Cerro Azul on the central coast of Peru. In 87 days, a total of 91 out of 722 (12.6%) cetaceans caught were Phocoena spinipinnis. Exploitation occurs in Peru and Chile, where the animals are shot or harpooned and subsequently sold for their meat, which is used as both bait in crab fisheries and consumed by humans. Purposeful catches have decreased since 1994 when stricter legislation was implemented, however the bycatches have not. The only known natural predator of Phocoena spinipinnis is the Killer whale.
IUCN Red List: Data Deficient
CITES: Appendix II
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