Porpoises are small cetaceans of the family Phocoenidae. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen. The most obvious visible difference between the two groups is porpoises have spatulate (flattened) teeth distinct from the conical teeth of dolphins. All seven species have small flippers, notched tail flukes, and no beaks. All carry at least 11 pairs of small teeth in their upper and lower jaws. [Source: Wikipedia]
Porpoise are divided into seven species. They live in all oceans and are generally found near the shore. Probably best known is the harbour porpoise, which can be found across the Northern Hemisphere. The seven species are: 1) Dall's porpoise (Phocoenoides dalli), size: 130–200 kilograms; 2) Harbour porpoise (Phocoena phocoena), size: 75 kilograms; 3) Spectacled porpoise (Phocoena dioptrica), size: 60–84 kilograms; 4) Burmeister's porpoise (Phocoena spinipinnis), size: 50–75 kilograms; 5) Indo-Pacific finless porpoise (Neophocaena phocaenoides), size: 30–45 kilograms; 6) Narrow-ridged finless porpoise (Neophocaena asiaeorientalis), size:30–45 kilograms; 7) Vaquita (Phocoena sinus), size: 30-50 kilograms;
Porpoises tend to be smaller than dolphins. Some of the species that live in more coastal regions such as harbor porpoises primarily feed on on pelagic (open ocean) fish such as herring, anchovies. Those that spend more time in the open ocean like Dall's porpoise forage primarily on fish and squid that live in deep water. The little evidence that exist about their feeding habits tends to indicate they usually forage individually rather than in groups.
Predators include orcas (killer whales), leopard seals and sharks. Not much is known unknown about anti-predator adaptations. But as is the case with many similar marine mammals, they have dark-at-the-top and light-at-the-bottom countershading that makes them more difficult to see if viewed seen from above or below. Presumably, they can swim fast and maneuver to escape predators. [Source: Ayaka Paul, Animal Diversity Web (ADW) /=]
Websites and Resources: Britain-based Whale and Dolphin Conservation Society uk.whales.org ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Difference Between Dolphins and Porpoises
Dolphins and porpoises differ in their faces, fins, and body shapes. Dolphins have longer noses, bigger mouths, more curved dorsal fins, and longer, leaner bodies than porpoises. Dolphins tend to have prominent, elongated “beaks” and cone-shaped teeth, while porpoises have smaller mouths and spade-shaped teeth. The dolphin’s hooked or curved dorsal fin (the one in the middle of the animal’s back) also differs from the porpoise’s triangular dorsal fin. Generally speaking, dolphin bodies are leaner, and porpoises’ are portly. [Source: NOAA]
Dolphins have a defined beak, a pronounced bulbous forehead and a more streamlined body while porpoises have spade a rounded head. They are also generally smaller than dolphins. Porpoise teeth are flat, like chisels, instead of round, like pegs. Dolphins and porpoises have many similarities, one of which is their extreme intelligence. Both have large, complex brains and a structure in their foreheads, called the melon, with which they generate sonar (sound waves) to navigate their underwater world. In addition, porpoises are relatively r-selected compared with dolphins: that is, they rear more young more quickly than dolphins.
Dolphins are by far more prevalent than porpoises. Most scientists agree that there are 32 dolphin species (plus five closely related species of river dolphin) and only six porpoise species. Dolphins are also more talkative than porpoises. Dolphins make whistling sounds through their blowholes to communicate with one another underwater. Scientists are pretty sure that porpoises do not do this, and some think this may be due to structural differences in the porpoise’s blowhole.
The genus Phocoena, sometimes referred to as common porpoises, is comprised of four species: 1) Harbour porpoise (Phocoena phocoena) (See Below); 2) Spectacled porpoise (Phocoena dioptrica); 3) Burmeister's porpoise (Phocoena spinipinnis); and 4) Vaquita (Phocoena sinus, Separate Article ioa.factsanddetails.com ).
Burmeisters porpoises are primarily found in coastal waters 100 to 1,000 meters from shore and from depths between 5 to 25 meters. They mostly feed on fish, shrimp, and squid and have an unobtrusive swimming style that makes them difficult to spot. These porpoises seem to hang out in groups with between two and eight individuals and can occasionally aggregate in larger groups. The largest such group observed had around 150 individuals. [Source: Ayaka Paul, Animal Diversity Web (ADW) /=]
Spectacled porpoises have only been rarely observed. Not much is known about their feeding behavior. When they are sighted they have been seen in pods consisting of between two to five animals.Like the Burmeisters porpoises they have unobtrusive swimming style that make them difficult to spot at sea./=\
Phocoenids generally have a relatively short life-span of approximately 20 years in the wild. These porpoises tend to reach sexual maturity early and grow rapidly. Additionally, they have a demanding reproductive schedule which goes in tandem with their shorter life-span. /=\
Common Porpoises Characteristics
Common porpoises have many similar morphological features. These mammals are small and retain traits from juvenile development into adulthood. Compared to dolphins they have shorter rostrums (snouts), smaller appendages, large and rounded braincases and small raised protuberances known as epidermal tubercles, which are found on the leading edge of the dorsal fin. Colortions vary with species. Often there darker pigmentation around the eyes, a bridle which is a “system of stripes extending from the eye and blowhole to the apex of the melon.” Females are larger than males. [Source: Ayaka Paul, Animal Diversity Web (ADW) /=]
Vaquitas have relatively larger flippers and a tall and falcate dorsal fin. Their most defining pigmentation are their black eye rings and lip patches. They have a broader and shorter rostrum compared to other species in this genus. Harbour porpoises are easy to identify with their its triangular-shaped dorsal fin and rotund shape.
Burmeister’s porpoises have their distinctive tubercles, dorsal fin that it is far back on the body and is triangular, and canted backwards. They are dark gray, lead gray or sometimes have a brownish hew with light gray to white portions around the abdomen. It also has a well defined eye patch with a light gray or white halo. The eye patch can extend to the lip patch. They also have stripes on its flipper and abdominal region. Spectacled porpoise juveniles have dark gray dorsal sides and light gray ventral sides with dark gray/brown streaks. This pigmentation changes in adults which have black dorsal surfaces and a contrasting white ventral region. Additionally, males in this species have a striking large dorsal fin. /=\
Porpoise Behavior, Communication and Reproduction
Porpoises can be found alone or in small groups. On some rarer occasions, they can form much larger aggregations, but these are likely more temporary and within these groups. There is often a female leader in groups and fission-fusion associations see to be the norm. Among the most long-lasting associations are those of a mother and calf. Porpoises tend to be shy, with the exception of the Dall's porpoises. They seldom leap out of the water or do dolphin-style acrobatics. Typically, when the break the ocean surface, they engage in a rolling behavior before submerging again for a long period of time. On calm days, they may stay slightly longer periods of times at the surface. [Source: Ayaka Paul, Animal Diversity Web (ADW) /=]
Porpoises sense using touch, sound, echolocation (emitting sound waves and sensing their reflections to determine the location of objects) and chemicals usually detected by smell. According to Animal Diversity Web: in the cases of harbour porpoises, research by Sørensen and colleagues in 2018 has shown that they produce only the narrow-band high-frequency (NBHF) clicks. These types of clicks are not necessarily well-suited for communication purposes however, they may still utilize sound within their limited social interaction. During these interactions they seem to utilize two categories of sound featuring high-repetition rate click trains. Additionally, when hunting vaquitas tend to use passive sound as opposed to echolocation when trying to detect their prey.
Porpoises are relatively r-selected compared with dolphins: that is, they rear more young more quickly than dolphins.In general, porpoises tend to reach sexual maturity early. Most porpoises have a gestation period of approximately 10-11 months. Harbour porpoises have a calving season that usually occurs between May-August, and this is followed by mating which occurs approximately 1.5 months after calving. Young are weaned before they turn one. Some are capable of getting some solid food at a few months old. They can become sexually mature between 3-4 years old but are not fully physically mature until they are around five for males and seven for females. For Burmeister’s porpoises, a study in Peru found the average length of sexual maturity in females is around 1.5 meters and 1.6 meters for males. This study also found that the mating season likely occurs between December-March, but there can occur outside this time Porpoises are thought be polygynandrous (promiscuous), with both males and females having multiple partners. There is a lot of sperm competition as male Harbor poises who produce large quantities of sperm. /=\
Harbor porpoises (Scientific name: Phocoena phocoena) are shy animals, most often seen in groups of two or three. They prefer coastal areas and are most commonly found in bays, estuaries, harbors, and fjords. Because they prefer coastal habitats, harbor porpoise are particularly vulnerable to gillnets and fishing traps, pollution, and other types of human disturbance, such as underwater noise. Their lifespan is About 24 years.[Source: NOAA]
Harbor porpoises live in northern temperate and subarctic coastal and offshore waters. They are commonly found in bays, estuaries, harbors, and fjords less than 200 meters (650 feet) deep. In the North Atlantic, they range from West Greenland to Cape Hatteras, North Carolina (but do not enter Hudson Bay), and from the Barents Sea to West Africa. In the North Pacific, they are found from Japan north to the Chukchi Sea and from Monterey Bay, CA to the Beaufort Sea. [Source: NOAA]
Harbour porpoises, also called common porpoises, primarily feed on schooling fish, like herring, pollack, hake, sardines, cod and mackerel. However, in some areas they also prey on squid, octopus, shrimp and other crustaceans. They feed near the sea bottom at depths less than 200 meters (657 feet) and can also forage near the surface. Generally, they feed independently but some have been observed working together to herd fish near the surface. It is possible that they use the surface of the ocean like wall when they herd prey from the sea bottom to feed. There is evidence that they reside in one area for extended periods of time. However, they also engage in onshore-offshore migrations. They have also been known to be able to dive up to 220 meters (720 feet). These porpoises have thick blubber and normally found alone or groups of two or three animals. [Source: Ayaka Paul, Animal Diversity Web (ADW) /=]
Harbor porpoises are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in seasonal breeding. The breeding season mainly occurs from June to September and most births occur between May and July. A female gives birth to one calf per year after a gestation period of around 11 months. The weaning age ranges from seven to eight months. Females and males reach sexual maturity at three to five years of age. Females may give birth every year for several years in a row. Lactation lasts for 8 to 12 months. Calves weigh six to eight kilograms (13 to 18 pounds) and are 70 centimeters to ione meter (2.3 to 3.3 feet) long. Mothers bring newborn calves to secluded coves to nurse. [Source: Andrew Masi, Animal Diversity Web (ADW) /=]
Harbor Porpoise Physical Characteristics
Harbor porpoises range in length from 1.5 to two meters (5 to 6.5 feet) and range in weight from 45 to 75 kilograms (100 to 165 pounds). Their average basal metabolic rate is 107.675 watts. Sexual dimorphism (differences between males and females) is slight but exists: Females are larger than males. [Source: Andrew Masi, Animal Diversity Web (ADW) /=]
Harbor porpoises have a small, robust body with a short, blunt beak. They have a medium-sized triangular dorsal fin that usually around 15 to 20 centimeters (6 to 8 inches) tall. There is no noticeable forehead or beak, and the snout is short, giving the head a somewhat cone-like shape. Harbour porpoises have two pectoral flippers, a single dorsal fin, and a tail with two partially separated flukes. All of these appendages are short and not very sharp. There is a noticeable keel located near the all dark tail flukes, with the tail itself spanning anywhere from 30 to 65 centimeters 1 to 2.2 feet). Inside the slightly upturned mouth there are rows of 16-28 spade-shaped teeth. There is no variance in the shape or type of teeth in Harbour porpoises. /=\
The back of harbor porpoises is dark gray while their belly and throat are white. The porpoises have a dark gray chin patch and also intermediate shades of gray along their sides. Coloration can vary from individual to individual, but the most common coloration pattern is a dark black or greay back (dorsal) surface that transitions to a lighter colored hue on the bottom (the ventral side). The flippers, dorsal fin, and tail are all dark in color, and there is a black stripe that runs from the edge of the mouth or eye to the flipper on either side.
Harbor Porpoise Behavior and Swimming
Harbor porpoises are motile (move around as opposed to being stationary), migratory (make seasonal movements between regions, such as between breeding and wintering grounds), territorial (defend an area within the home range), and social (associates with others of its species; forms social groups). [Source: Andrew Masi, Animal Diversity Web (ADW) /=]
Harbor porpoises are most often seen singly, in pairs, or in groups of up to 10, although there are reports of aggregations of up to 200 harbor porpoises. When the larger groups do occur, it is usually because a number of smaller groups join together to exploit a rich food source. Some populations migrate, but when they return to their regular waters they are territorial, patrolling certain areas./=\
Most seasonal movements appear to be inshore-offshore and may be influenced by prey availability or the presence of ice-free waters. Unlike many other dolphins and porpoises, they do not approach boats to bow ride and rarely jumping out of the water. When surfacing for air, they do not splash. They roll from beak to fluke and arch their backs. [Source: NOAA]
Harbor porpoises usually swim near the surface, rising to the surface to breath about every 25 seconds, and do not move particularly fast on a routine basis, but when pursued or threatened can reach speeds of around 23 kilometers per hour. (14 miles per hour). When diving they saty submerged for an average of four minutes and reach depths of 200 meters (650 feet).
Harbor porpoises sense using vision, touch and chemicals usually detected with smell. They produce click-like sounds similar to those used by other cetaceans as a means of echolocation (emitting sound waves and sensing their reflections to determine the location of objects) in order to locate food and navigate in their surroundings. /=\
Harbor Porpoises, Humans and Conservation
Harbor porpoises are generally not considered endangered or threatened. But some populations may be. However, they are classified as “Critically Endangered” on the International Union for Conservation of Nature (IUCN) Red List. TheConvention on International Trade in Endangered Species (CITES) places them in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. They are protected throughout their range by the Marine Mammal Protection Act (MMPA).
One of the main threats to harbor porpoises is getting caught in fishing gear. They can become entangled or captured in commercial fishing gear such as gillnets, trawls, and herring weirs (in Canada). Underwater noise pollution interrupts the normal behavior of harbor porpoises and interferes with their communication. [Source: NOAA]
In some places harbor porpoises have traditionally been hunted for meat to eat and oil used in lamps and as a lubricant. The practice may still continue. Fishing of harbour porpoises is now illegal in most areas and efforts have been made to reduce catching and killing porpoises as bycatch in commercial fishing. Nets are sometimes placed in nearshore areas where Harbour porpoises reside.[Source: Andrew Masi, Animal Diversity Web (ADW) /=]
Some threats they face are natural. A number of porpoise carcasses found in Scotland all had similar puncture and bruise wounds, with most of them dying as a result of internal injury. In addition to these injuries some of the specimens also had teeth gouges in their flesh. After analyzing these bite patterns, the researchers determined that common bottlenose dolphin were responsible for inflicting these wounds.
Dall’s porpoises (Scientific name:Phocoenoides dalli) are considered the fastest swimmers among small cetaceans, reaching speeds of 55 kilometers per hour (34 miles per hour) over short distances. They are named for W.H. Dall, an American naturalist who collected the first specimen of this species. A special characteristic of Dall’s porpoises is their distinctive color pattern: a black body with a conspicuous white lateral patch on the left, right, and underside. They are often mistaken for baby killer whales, but unlike killer whales, their dorsal fins are triangle-shaped and they do not have eye patches or saddle patches. Their lifespan is 15 to 20 years. [Source: NOAA]
The International Union for Conservation of Nature (IUCN) estimates there are about 1.1 million Dall's porpoise worldwide. In the western North Pacific Ocean, there are an estimated 104,000 Dall’s porpoises off of Japan, 554,000 in the Okhotsk Sea, 100,000 in the U.S. West Coast stock, and 83,000 in Alaska. Killer whales and sharks are believed to be the primary natural predators of Dall's porpoises. They can escape predation through their large body size, speed, agility in the water, and their habit of traveling in groups. Their coloration may make them difficult to see in the water as well.
Dall’s porpoises can dive up to 500 meters (1,640 feet) to feed on small schooling fish (such as, anchovies, herring, and hake), mid- and deep-water fish (such as, myctophids and smelts), cephalopods (such as, squid and octopus), and occasionally crustaceans (such as, crabs and shrimp). Feeding usually occurs at night when their prey migrates up toward the surface. They have 38 to 56 very small, spade-shaped teeth (about the size of a piece of grain or rice) on each jaw that are useful for grasping. Food species as determined from stomach contents have included squid and other cephalopods, lanternfish, Pacific hake, jack mackerel, herring, sardines, and crustaceans. Mid-level and deep water open ocean species and and deep-water, bottom-species are present in their diet. [Source: Jeffrey Decker, Animal Diversity Web (ADW); NOAA]
Dall's Porpoise Habitat, Subspecies and Where They Are Found
Dall’s porpoises prefer temperate to boreal (northern, cold) waters that are more than 200 meters (656 feet) deep and with temperatures between 2° and 17°C.(36° and 63°F). They can be found in offshore, inshore, and nearshore oceanic waters, between 30° north and 62° north. Migration patterns (mainly inshore-offshore and north-south) are based on morphology- type, geography, and seasonality. [Source: NOAA**]
Dall's porpoises occur throughout the coastal and pelagic waters of the North Pacific Ocean. This species is commonly found in the Gulf of Alaska, Bering Sea, Okhotsk Sea, and Sea of Japan. In the eastern North Pacific, they can be found from around the U.S./Mexico border (Baja California, 32° north) to the Bering Sea, in the central North Pacific (above 41° north), and in the western North Pacific from central Japan (35° north) to the Okhotsk Sea. In the Bering Sea, Dall’s porpoises occur in higher abundance near the shelf break. They are commonly seen in inshore waters of Washington, British Columbia, and Alaska. For management purposes, Dall's porpoises inhabiting U.S. waters have been divided into the Alaska stock and the California-Oregon-Washington stock. **
Although they favor cooler water, Dall's porpoises are found in the warmer waters of Baja California on the east to southern Japan on the west. They are frequently observed in these lower latitudes during the winter months. Dall’s porpoises are a deep water species but they are observed inshore and offshore. When they approach the coast they usually do so by following canyons or deep channels. They are also commonly observed in sounds and inland passages where these meet the open sea. [Source: Jeffrey Decker, Animal Diversity Web (ADW) /=]
There are two subspecies of Dall's porpoises that are currently recognized based on distinguishable color patterns: 1) Phocoenoides dalli d. truei and 2) Phocoenoides dalli dalli. The truei-type is abundant only in waters around the Kuril Islands and off the Pacific coast of northern Japan, while the dalli-type ranges across the northern North Pacific — from northern Japan to the Bering Sea and into California. Other variable and hybrid types (with harbor porpoises) are also relatively common. **
Dall's Porpoise Physical Characteristics
Dall's porpoises are the largest of all phocoenids (porpoises). They reach the length of 2.2 meters (7.2 feet), with their average length being 1.8 to 2 meters (6 to 6.5 feet). They range in weight from 130 to 220 kilograms (286 to 484 pounds). Sexual Dimorphism (differences between males and females) is not very pronounced. Both sexes are roughly equal in size and look similar. [Source: Jeffrey Decker, Animal Diversity Web (ADW) /=]
Dall's porpoises are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them), homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings) and are polymorphic (“many forms”, species in which individuals can be divided into easily recognized groups, based on structure, color, or other similar characteristics).
Dall's porpoises have a relatively small, triangular head with little or no beak and a thick, robust body. Their flippers are small, round, and located near the front of the body. The triangular dorsal fin is positioned in the middle of the back, and often angles forward. The tail stock and keel (where the caudal fin attaches to the body) are exaggerated and create a pronounced hump, which is large compared to other marine mammals. Adult males have a thicker tail stock and forward-projecting dorsal fin. [Source: NOAA]
Their coloration is very dark gray or black with contrasting white markings on the dorsal fin and tail that distinguish Dall’s porpoises from other cetaceans. All-black (melanistic) and all-white (albino) forms also exist but are considered rare. Markings and colorations vary by geographic location and life stage, with adults having more distinct colorations. Adults also have a chunkier and more robust body than juveniles.
There are three color patterns observed in the Dall's porpoises. 1) a uniform black or white throughout the entire body; 2) intermixed stripes of black and white running along the length of the body; and .3) the color pattern observed, that of P. dalli dalli, the most common type. In the latter the dorsal (back) area uniformly black with a white ventral side. The white ventral patch begins far behind the flippers. The dorsal fin, flippers, and fluke are black with some white at the tips. The color pattern of P. dalli truei is different only in the distribution of the white ventral patch. The white patch begins ahead of the flippers rather than far behind them, and P. dalli truei is often longer and slimmer than P. dalli dalli. /=\
Dall's Porpoise Behavior
Dall’s porpoises are motile (move around as opposed to being stationary), migratory (make seasonal movements between regions, such as between breeding and wintering grounds), and social (associates with others of its species; forms social groups). Migration north in summer and south in winter has been reported. [Source: Jeffrey Decker, Animal Diversity Web (ADW) /=]
Dall’s porpoises are usually found in groups averaging between two and 20 individuals, but they have been occasionally seen in larger, loosely associated groups in the hundreds or even thousands of animals. They are known to associate with Pacific white-sided dolphins and short-finned pilot whales but have also been seen swimming alongside large whales such as gray whales. They are sometimes seen with harbor porpoises, especially in the deep waters off Alaska and in Prince William Sound. As rapid, social swimmers, Dall’s porpoises are also attracted to fast moving vessels and commonly bowride beside ships. They briskly surface while swimming, creating a "rooster tail" of water spray that is a unique characteristic of the species. [Source: NOAA]
Dall's porpoises do not display the typical shy behavior of most other porpoises. They are frequently seen charging boats and often swim in a zig-zag pattern with fast, jerky, steep angled turns. Dall's porpoises may surface with a slow roll, a fast roll, or a rooster-tailing roll. The rooster-tailing roll is often used to identify the species in the wild. The spray resulting from this roll is a cone of water coming off the head of the porpoise which looks like a "rooster tail" due to the quick speed and steep angles at which the species surfaces.
Dall's porpoises communicate with touch and sound and sense using vision, touch, sound and chemicals usually detected with smell. They emit low-frequency clicks that are presumably used for echolocation (emitting sound waves and sensing their reflections to determine the location of objects) to navigate, capture prey, and perhaps to communicate with members of their species. They also use a variety of audible clicks and whistles. They may also use touch for social communication. /=\
Dall's Porpoise Mating, Reproduction, Offspring and Development
Dall's porpoises are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in seasonal breeding. A single calf is born, usually between June and September. Individual females probably do not breed every year. Breeding intervals may be as long as three to 4 years because of the length of dependence of calves. The average gestation period is 11 months. The average weaning age is 24 months. Females reach sexual maturity at three to six years. Males reach sexual maturity at five to eight years. [Source: Jeffrey Decker, Animal Diversity Web (ADW) /=]
Little is known about mating habits of cetaceans, especially species which occur primarily offshore like Dall's porpoises. Mating likely occurs after the calving seasons each year which takes place in winter, from February to March, and in summer, from July to August., with the average number of offspring being one. Hybrids between Dall's porpoises and harbor porpoises are also fairly common in the northeast Pacific but can also occur elsewhere. Phocoenoides dalli dalli appear to have three major breeding grounds. Two occur in the North Pacific north of 45 degree latitude, and another breeding site occurs in the central Bering Sea. Phocoenoides dalli truei may breed off the northern coast of Japan. [Source: NOAA, /=]
Young and are relatively well-developed when born. During the pre-birth, pre-weaning and pre-independence stages provisioning and protecting are done by females. Females feed and care for their offspring for extended periods of time. There is an extended period of juvenile learning. Males are nnot involved in parental care.
At birth, calves are generally 0.85 to 1.0 meters (2.8 to 3.3 feet) long and are nursed by their mother for less than one year. Two calving periods have been reported for portions of the eastern North Pacific, one in winter, from February through March, and the other in summer, from July through August. According to Animal Diversity Web: Some segregation of animals seems to occur with juveniles found closer to shore and larger adults well offshore. In offshore areas, females in late pregnancy or lactation seem to be distributed in northern areas, and southern areas are mainly occupied by males and females not accompanied with calves. This seems to indicate that not all females become pregnant every year. Females usually reach sexual maturity between the age of three to six years, whereas males reach sexual maturity between the ages of five to eight years. Gestation is believed to last about 11 months, and lactation periods are usually about two years. /=\
Dall's Porpoises, Humans, Threats and Hunting
Dall’s porpoises, are not endangered or threatened.. They are designated as a species of least concern on the International Union for Conservation of Nature (IUCN) Red List. The Trade in Endangered Species (CITES) places them in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. Dall’s porpoises, like all marine mammals, are protected under the Marine Mammal Protection Act.
Threats include entanglement in fishing gear, hunting, habitat alteration, contaminants and ocean noise. Underwater noise pollution interrupts the normal behavior of Dall’s porpoises and interferes with their communication. Contaminants enter ocean waters and sediments from many sources — such as wastewater treatment plants, sewer outfalls, and pesticide application — and move through the food chain. Pollutants and various contaminants in the marine environment have been found in the blubber of Dall's porpoises. These pollutants can harm their immune and reproductive systems. Modern pollution controls have reduced but not eliminated many chemical contaminants, which continue to threaten Dall's porpoises. Additionally, some of these contaminants persist in the marine environment for decades and continue to threaten marine life. [Source: NOAA]
One of the main threats to Dall’s porpoises is becoming entangled or captured in commercial fishing gear such as drift nets, gillnets, and trawls. This occurs in fisheries targeting groundfish, salmon, and squid in Canadian, Russian, Japanese, Alaskan, and other U.S. waters. Once entangled, porpoises can become anchored or may swim off with the gear attached for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury, which may lead to reduced reproductive success and death. [Source: NOAA]
Japanese fisherman hunt Dall’s porpoises in the western North Pacific as a source of meat for human consumption. About 18,000 Dall’s porpoises are taken annually. Dall's porpoises were intensely hunted in the western Pacific during the 1980s. Estimates suggested 40,367 Dall's porpoises were killed in 1989 from the Japanese hand-harpoon fishery alone. In recent years these numbers have declined because of the Japanese government's effort to regulate the hand-harpooning of these animals. In 1992 11,403 were killed. It has been estimated that up to 20,000 porpoises are entangled and drowned in fishing nets off of Japan and up to about 4,100 off of North America annually. New regulations, fishing gear and techniques have significantly reduced the incidental capture and killing of porpoises and dolphins. drastically. [Source: Jeffrey Decker, Animal Diversity Web (ADW) /=]
Vaquitas (Scientific name: Phocoena sinus) are the world’s smallest porpoises and one of the world's most endangered animals. Less than 30 vaquitas remain in the wild, and and they all live in the northern reaches of the Gulf of California, Mexico. The population of the species is falling at an alarming rate mainly because of accidental entanglement in gillnets and other fishing gear. The animal’s slow maturation and low birthrate compound the problem. It is considered likley that they will become extinct. [Source: NOAA; Robert L. Pitman and Lorenzo Rojas-Bracho, Natural History magazine, July -August 2007]
Vaquitas are shy members of the porpoise family. The are the smallest Cetaceans (whale, dolphins and porpoises). The only sea mammals that are smaller are sea otters. Vaquitas were first recognized as a new species in 1958, on the basis of three skulls found on beaches in the northern Gulf of California. A quarter century passed before a live animal was scientifically documented, and only in 1985 were its external features first described by biologists.
Little is known about the vaquita's biology or life history. Because the animal is shy as well as rare, it has not readily disclosed its secrets. But what little is known does not bode well for its future. The normal lifespan is probably twenty years or more. It reaches sexual maturity between three and six years of age, and females apparently give birth to a single calf every other year. It typically travels alone or in mother-and-calf pairs. Their lifespan is About 20 years.
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated June 2023