Porpoises

(Phocoenidae)

Class Mammalia

Order Cetacea

Suborder Odontoceti

Family Phocoenidae

Thumbnail description
Small to medium dolphin-like aquatic carnivores with dark gray to black body covering and a pale gray underbelly, the absence of a distinct beak, compressed spatula-shaped teeth, fused neck vertebrae, small triangular-shaped dorsal fins, and a rounder shape than their dolphin relations

Size
4.8–6.5 ft (1.4–2.0 m); 90–485 lb (40–220 kg)

Number of genera, species
3 genera; 6 species

Habitat
Oceans, bays, harbors, estuaries, rivers; deep, shallow, benthic, and pelagic

Conservation status
Critically Endangered: 1 species; Threatened: 1 species; Lower Risk/Conservation Dependent: 1 species; Data Deficient: 3 species

Distribution
Globally distributed across the northern Pacific and Atlantic Oceans, along the coasts of South America, and the northern and southern Indian Ocean

Evolution and systematics

While dolphins and porpoises are both related to the squalodonts (earliest true-toothed whales) and the kentridontids (ancestral dolphins), porpoises have been distinct and set apart from dolphins for approximately 11 million years.

Porpoises started to appear in the fossil record during the Miocene epoch, around 10 to 12 million years ago (mya). Scientists conjecture that they probably resembled modern-day finless porpoises, Neophocaena phocaenoides, and lived in the same type of habitat—the warm, tropical waters of the Pacific Ocean.

According to the fossil record, the original Neophocaenid ancestor that later colonized the temperate and subarctic regions of the North Pacific from the late Miocene onwards, most likely gave rise to the genus Phocoenoides, to which the Dall's porpoise (P. dalli) also belongs. The Phocoenid porpoises emerged sometime in the middle of the Pliocene. By that time, the genus Phocoena appeared to have already colonized both the Northern and Southern Hemispheres. It has been hypothesized that their migratory movements most likely coincided with the equatorial inflow of cooler subtropical waters during the cooler periods of the Pliocene, or in another scenario, during the glacial intervals in the Pleistocene. The original ancestor in the north is believed to have led to the emergence of the harbor porpoise (P. phocoena), while its southern radiations resulted in at least two other species—Burmeister's porpoise (P. spinipinnis) and the spectacled porpoise (P. dioptrica).

The vaquita (P. sinus), believed to be the "youngest" species in the genus, appears to have descended from the modern Burmeister's porpoise after it migrated to the Northern Hemisphere during the cooler periods of the late Pleistocene but was later cut off in the upper Sea of Cortez when tropical waters warmed up and the last glaciers made their retreat.

Physical characteristics

Typical of most porpoises is the absence of a forehead or beak on their small rounded heads. The six neck vertebrae of a porpoise are extremely foreshortened and fused together to create an immobile neck, with the body tapering down to a pair of notched flukes. Contrary to the hooked or curved dorsal fins of dolphins, the ones found in most porpoises are well defined and triangular in shape and matched by small pointed or rounded flippers usually positioned near the head. The leading edge of the dorsal fin may also be lined with rows of tubercles, or circular bumps. Unlike the homodont, conical teeth of dolphins, porpoises possess spatulate (spade-shaped) teeth in both jaws.

While female porpoises are generally larger than the males—except in spectacled porpoises, where the reverse holds true—a considerable range of morphological variation exists between the different species of porpoises. Differences in stockiness, robustness, and coloration can sometimes occur even within individual species. For instance, three different color patterns have been observed in Dall's porpoise alone:

uniform black or uniform white; inter-mixed stripes of black and white across the length of the body; and a solid black dorsal portion with a white underside. The finless porpoise, which resembles a small Beluga whale (Delphinapterus leucas), has a light coloration which darkens slightly with age and quickly turns black after death. Eight stocks of Dall's porpoise, found in the Pacific waters of Japan, are recognized by the International Whaling Commission, with each stock having its own unique color morphotype.

Most species have significant characteristics that distinguish them from one another. The spectacled porpoise has eyes surrounded by a black circle edged in white, giving the illusion that the mammal is wearing eyeglasses. The finless porpoise has a lack of dorsal fin, while the harbor porpoise has a pronounced keel, or distinctive bulge on the tail stock near the flukes.

Distribution

It is commonly believed that porpoises originated in the North Pacific and then later spread to the Atlantic and southern waters, although they can be sighted today in rivers and estuaries as well. Harbor porpoises can be found in the temperate waters of the Northern Hemisphere and generally inhabit coastal waters with a depth of less than 500 ft (152 m). In fact, their common name is derived from regular appearance in bays and harbors. Spectacled porpoises are only found in the temperate and subantarctic waters of the Southern Hemisphere, while Burmeister's porpoises can only be located in the coastal waters of South America, around the southern coastline of Tierra del Fuego towards northern Peru.

Dall's porpoises are only found in the Pacific Ocean in the Northern Hemisphere and range across the entire North Pacific at latitudes greater than 32°N but not any further beyond the lower, deeper half of the Bering Sea. Generally oceanic in nature, they also appear to prefer cold waters and are not usually found in the southern extremes of their range during the summer months.

Vaquitas, the smallest of all porpoises and perhaps even all cetaceans, have the most restricted range of any marine cetacean as they appear to live only in the northern end of the Gulf of California. Most sightings of vaquita are in shallow water of less than 130 ft (40 m) and within 16 mi (25 km) of shore.

More widely distributed are the finless porpoises, which can be found in the coastal waters of Asia from the Persian Gulf, east and north to central Japan, and as far south as the northern coast of Java and the Strait of Sunda. Frequently sighted near the coast, they are described as a coastal, estuarine, or riverine species.

Studies of the harbor porpoise in Monterey Bay suggest a seasonal north-to-south migratory pattern along the coast of California, according to the seasonal availability of prey items. While this wide range of distribution suggests a significant population of harbor porpoises, specific numbers remain unknown.

Habitat

Because of their long-range migratory patterns, porpoises live in a variety of habitats. While the spectacled porpoise prefers the cold temperate waters and subantarctic waters of the Southern Hemisphere, specifically the coastal waters of eastern South America, for instance, the finless porpoise prefers saltwater and freshwater environs, such as estuaries, mangroves, and rivers. Porpoises may be both benthic or pelagic. For example, Burmeister's porpoises inhabit the shallow temperate waters of coastal South America, but Dall's

porpoises are found in the deeper waters of the northern North Pacific and Bering Sea.

Behavior

Frequently elusive, secretive, unapproachable, and wary of human presence, porpoises are rarely observed in groups of more than a few individuals. Vaquitas in particular intentionally seem to avoid boats. On the other hand, the Yangtze River populations of finless porpoises are atypically unfazed by boats or people, probably because they have become accustomed to the river's heavy traffic. They have also been observed in groups of five to 10 individuals and even in pods of 50 members, perhaps in order to take advantage of rich feeding grounds.

Feeding ecology and diet

Dietary preferences naturally follow the range of habitat that porpoises are situated in. Harbor porpoises are deep divers, capable of reaching depths in excess of 650 ft (200 m) and their diet tends to consist of herring, capelin, and gadoid fishes such as pollack and hake. Recently weaned porpoises eat euphausiid shrimp. Vaquitas, on the other hand, feed primarily on teleost fishes and squids that are commonly found in the demersal and benthic zones of the shallow waters of the upper Gulf of California, while Burmeister's porpoises feed primarily on anchovy and hake, although squid, mysid shrimp and euphasiids are also consumed. Burmeister's porpoises in Chilean waters also appear to eat mollusks. In the Pacific Ocean, Dall's porpoises feed on a wide variety of fish and cephalopods, most of which are deepwater or vertically migratory in nature. Almost nothing is known about the food preferences of spectacled porpoises although a single stranded animal found in Argentina had anchovy and small crustaceans in its stomach.

Reproductive biology

Porpoises, on average, become sexually mature between three and five years of age, after which the females produce one calf annually. Calving season for Dall's porpoises take place during the summer from June to September and gestation lasts about 11 months. Subsequently, mothers tend to nurse their young for approximately two years.

Knowledge of porpoise reproductive biology is not uniform for the various species. The vaquita, because of its elusiveness, is virtually undocumented, although it has been noted that their juveniles have white spots on the leading edge of the dorsal fin.

Conservation status

Many harbor porpoise populations around the world have been depleted through bycatch by fisheries, with chemical and noise pollution acting as a contributing factor. In North America alone, bottom-set gill nets catch hundreds of porpoises annually. This has led some countries to afford them special status. In Atlantic Canada, harbor porpoises are listed as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Northwest Atlantic harbor porpoises are designated as a Strategic Stock under the U. S. Marine Mammal Protection Act (MMPA) because current levels of killing exceed the estimated Potential Biological Removal (PBR) level for the population. Under the IUCN Red List of Threatened Species, harbor porpoises are listed as Vulnerable.

Very little is known about the abundance of the vaquita, although a 1997 abundance survey, jointly conducted by the National Fisheries Institute of Mexico and the U.S. National Marine Fisheries placed an estimate at 547 animals, with a 95% confidence interval of between 177 and 1,073 individuals. Vaquitas are currently listed on the IUCN Red List of Threatened Species as Critically Endangered. The greatest

threat to remaining populations of vaquita is incidental mortality in fishing gear since vaquitas are known to die in gill nets legally set for sharks, rays, mackerel, and chano, and illegal but occasionally permitted gill nets set for totoaba (Totoaba macdonaldi), an endangered species of fish.

There are no abundance estimates for the spectacled porpoises, Burmeister's porpoises, or finless porpoises, although bycatch and the occasional harpooning for bait or human consumption are also seen as the largest threats to their populations. The IUCN list them as Data Deficient under the Red List of Threatened Species. Threats to finless porpoises in the Yangtze River include incidental mortality from entanglement in passive fishing gear, electric fishing, collisions with powered vessels, and exposure to explosives used for harbor construction. Most of their habitat, according to the IUCN, has undergone severe degradation due to the damming of the Yangtze tributaries and the high volume of traffic in the river.

Significantly more abundant are the Dall's porpoises, which are listed as Lower Risk/Conservation Dependent by IUCN. One estimate places their numbers in the North Pacific and Bering Sea at 1,185,000. Despite their existing numbers, these porpoises have also been taken in large numbers in a variety of Asian-based pelagic drift net fisheries for salmon and squid. Directed fisheries may also pose a threat to their populations.

Several mitigation measures have been put in place to reduce the large bycatches of porpoises, including an acoustic deterrent device known as a "pinger," which alerts porpoises to echolocate in the presence of nets. However, it was discovered that harbor porpoises habituate to pingers, thus reducing their effectiveness over time.

Significance to humans

From the 1830s until the end of World War II, a major fishery for harbor porpoises in the Lille Bælt in Denmark took several hundred to more than a thousand animals annually. Before Turkish fisheries were suspended in 1983, 34,000–44,000 animals were taken per year between 1976 and 1981, with harbor porpoises making up about 80% of the total catch.

Species accounts

List of Species

Harbor porpoise

Phocoena phocoena

subfamily

Phocoenidae

taxonomy

Phocoena phocoena (Linneaus, 1758), Baltic Sea.

other common names

English: Common porpoise; French: Marsouin commun.

physical characteristics

Length 4.9–6.6 ft (1.5–2.0 m); weight 99–143 lb (45–65 kg). Forehead and beak are absent from the head; mouth is short and straight while curving slightly at the ends; dorsal side is often deep brown or gray; ventral side ranges from light gray to white; lips and chin are black; black lines extend from the jawline to the flippers.

distribution

Mainly in the North Atlantic and northern Pacific, with populations in western Europe and the North American coasts; a seasonal north-to-south migratory pattern along the coast of California. A 1995 ship survey in northern California found a specific distribution according to water depth—significantly more porpoises than expected occurred at depths of 65–200 ft (20–60 m) and fewer at depths of more than 200 ft (60 m). There is also a colony of harbor porpoises in the Mediterranean Sea.

habitat

Coastal temperate and subarctic waters of the North Atlantic and northern Pacific; bays, rivers, estuaries, and tidal channels in Western Europe and both coasts of North America.

behavior

Secretive and seldom observed in the wild; can be identified by the distinct sound it produces, which is a puffing noise resembling a sneeze.

feeding ecology and diet

Mostly cephalopods and fishes; schooling non-spiny fishes such as herring, mackerel, and sardine.

reproductive biology

Mating season occurs in the summer, from June to October after a gestation period of 11 months; age and length of sexual maturity is still being debated.

conservation status

Listed as Threatened by COSEWIC; Strategic Stock under the U. S. MMPA; Vulnerable by the IUCN Red List of Threatened Species. Bycatches are known to be high in the North Sea, and in France, Spain, and Portugal, although the extent of these bycatches is unknown.

significance to humans

Direct fishing for food and oil.

Burmeister's porpoise

Phocoena spinipinnis

subfamily

Phocoenidae

taxonomy

Phocoena spinipinnis Burmeister, 1865, Buenos Aires, Argentina.

other common names

English: Black porpoise; French: Marsouin de Burmeister; Spanish: Marsopa espinosa.

physical characteristics

Length 4.6–5.9 ft (1.4–1.8 m); weight 88–154 lb (40–70 kg); dorsal side is dark gray to black in color; ventral portion is slightly lighter; referred to as the "black porpoise" because it turns completely black after death.

distribution

Mostly in the Atlantic and Pacific Oceans, along the coastal waters of South America—the coast of Brazil, south along the coastlines of Tierra del Fuego, and the Falkland Islands north into the coastal Pacific waters of Peru.

habitat

Shallow waters of less than 500 ft (152 m) depth; rivers and estuaries; coasts bordering the Atlantic and Pacific Oceans.

behavior

Travel is usually in small groups, although observers have rarely found more than eight individuals together at any one time. They swim in quick, jerky movements but remain fairly inconspicuous and barely break the surface of the water when they come up to breathe. Burmeister's porpoises are very timid and scatter rapidly when approached by boats, and can be identified on the surface by respiration sounds.

feeding ecology and diet

Primarily anchovies and hake. Also squid, euphasiids, mysid shrimp, up to nine species of fish, and mollusks.

reproductive biology

Sexual maturity peaks at an average length of 61 in (155 cm) for males and 63 in (160 cm) for females; mating season occurs from June to September, with calving in May through August after a gestation of 10 months.

conservation status

Listed as Data Deficient by the IUCN.

significance to humans

Like most cetaceans, Burmeister's porpoises are frequently inadvertent bycatch in fishing nets. In Peru and Chile, animals are shot or harpooned and then sold for their meat, either as bait in crab fisheries or for human consumption. After stricter legislation was implemented in 1994, purposeful catches have declined, although bycatches have not.

Resources

Books

Gaskin, D. E. The Ecology of Whales and Dolphins. London: Heinemann Educational Books Ltd., 1982.

Jefferson, T. A., S. Leatherwood, and M. A. Webber. The Marine Mammals of the World. FAO Species Identification Guide. Rome: United Nations Environmental Programme, 1993.

Klinowska, M. Dolphins, Porpoises and Whales of the World. The IUCN Red Data Book. Gland, Switzerland: IUCN, 1991.

Perrin, W. F., G. P. Donovan, and J. Barlow. Gillnets and Cetaceans. Cambridge: International Whaling Commission, 1994.

Ridgeway, S. H., and R. Harrison, eds. Handbook of Marine Mammals. Vol. 6, The Second Book of Dolphins and Porpoises. San Diego: Academic Press, 1999.

Tolley, K. A. Population Structure and Phylogeography of Harbor Porpoises in the North Atlantic. Bergen, Norway: Department of Fisheries and Marine Biology, University of Bergen, 2001.

Periodicals

Caretta, J. V, B. L. Taylor, and S. J. Chivers. "Abundance and Depth Distribution of Harbor Porpoise (Phocoena phocoena) in Northern California Determined From a 1995 Ship Survey." Fish Bulletin 99, no. 1 (2001): 29–39.

Cox, T. M., A. J. Read, A. Solow, and N. Trengenza. "Will Harbor Porpoises (Phocoena phocoena) Habituate to Pingers?" Journal of Cetacean Research and Management 3, no. 1 (2001): 81–86.

Frantzis, A., J. Gordon, G. Hassidis, and A. Komnenou. "The Enigma of Harbor Porpoise Presence in the Mediterranean Sea." Marine Mammal Science 17, no. 4 (2001): 937–944.

Law, T. C., and R. W. Blake. "Swimming Behaviors and Speeds of Wild Dall's Porpoises (Phocoenoides dalli)." Marine Mammal Science 10, no. 2 (1994): 208–213.

Sekiguchi, K. "Occurrence, Behavior and Feeding Habits of Harbor Porpoises (Phocoena phocoena) at Pajaro Dunes, Monterey Bay, California." Aquatic Mammals 21, no. 2(1995): 91–103.

Jasmin Chua, MS