Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the walrus), Otariidae (the eared seals: sea lions and fur seals), and Phocidae (the earless seals, or true seals), with 34 extant species and more than 50 extinct species described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic group (descended from one ancestor). Pinnipeds belong to the suborder Caniformia of the order Carnivora; their closest living relatives are musteloids (weasels, raccoons, skunks and red pandas), having diverged about 50 million years ago.
Seals range in size from the and Baikal seal to the and southern elephant seal. Several species exhibit sexual dimorphism. They have streamlined bodies and four limbs that are modified into flippers. Though not as fast in the water as dolphins, seals are more flexible and agile. Otariids primarily use their front limbs to propel themselves through the water, while phocids and walruses primarily use their hind limbs for this purpose. Otariids and walruses have hind limbs that can be pulled under the body and used as legs on land. By comparison, terrestrial locomotion by phocids is more cumbersome. Otariids have visible external ears, while phocids and walruses lack these. Pinnipeds have well-developed senses—their eyesight and hearing are adapted for both air and water, and they have an advanced tactile system in their whiskers or vibrissae. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in cold water, and, other than the walrus, all species are covered in fur.
Although pinnipeds are widespread, most species prefer the colder waters of the Northern and Southern Hemispheres. They spend most of their lives in water, but come ashore to mate, give birth, molt or to avoid ocean predators, such as sharks and orcas. Seals mainly live in marine environments but can also be found in fresh water. They feed largely on fish and marine invertebrates; a few, such as the leopard seal, feed on large vertebrates, such as penguins and other seals. Walruses are specialized for feeding on bottom-dwelling mollusks. Male pinnipeds typically mate with more than one female (polygyny), though the degree of polygyny varies with the species. The males of land-breeding species tend to mate with a greater number of females than those of ice breeding species. Male pinniped strategies for reproductive success vary between defending females, defending territories that attract females and performing ritual displays or lek mating. Pups are typically born in the spring and summer months and females bear almost all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively short period of time while others take foraging trips at sea between nursing bouts. Walruses are known to nurse their young while at sea. Seals produce a number of vocalizations, notably the barks of California sea lions, the gong-like calls of walruses and the complex songs of Weddell seals.
The meat, blubber and skin of pinnipeds have traditionally been used by indigenous peoples of the Arctic. Seals have been depicted in various cultures worldwide. They are commonly kept in captivity and are even sometimes trained to perform tricks and tasks. Once relentlessly hunted by commercial industries for their products, seals are now protected by international law. The Japanese sea lion and the Caribbean monk seal have become extinct in the past century, while the Mediterranean monk seal and Hawaiian monk seal are ranked as endangered by the International Union for Conservation of Nature. Besides hunting, pinnipeds also face threats from accidental trapping, marine pollution, climate change and conflicts with local people.
Etymology
The name "pinniped" derives from the Latin words and . The common name "seal" originates from the Old English word , which is in turn derived from the Proto-Germanic .
Taxonomy
The German naturalist Johann Karl Wilhelm Illiger was the first to recognize the pinnipeds as a distinct taxonomic unit; in 1811 he gave the name Pinnipedia to both a family and an order. American zoologist Joel Asaph Allen reviewed the world's pinnipeds in an 1880 monograph, History of North American pinnipeds, a monograph of the walruses, sea-lions, sea-bears and seals of North America. In this publication, he traced the history of names, gave keys to families and genera, described North American species and provided synopses of species in other parts of the world. In 1989, Annalisa Berta and colleagues proposed the unranked clade Pinnipedimorpha to contain the fossil genus Enaliarctos and modern seals as a sister group. Pinnipeds belong to the order Carnivora and the suborder Caniformia (known as dog-like carnivorans). Of the three extant families, the Otariidae and Odobenidae are grouped in the superfamily Otarioidea, while the Phocidae belong to the superfamily Phocoidea. There are 34 extant species of pinnipeds, and more than 50 fossil species of pinnipedimorphs.
Otariids are also known as eared seals due to their pinnae. These animals swim mainly using their well-developed fore-flippers. They can also "walk" on land by shifting their hind-flippers forward under the body. The front end of an otariid's frontal bone protrudes between the nasal bones, with a large and flattened supraorbital foramen. An extra spine splits the supraspinatous fossa and bronchi that are divided in the front. A 2021 genetic study found that pinnipeds are more closely related to musteloids. Pinnipeds split from other caniforms 50 million years ago (mya) during the Eocene. The earliest fossils of pinnipeds date back to the Late Oligocene. Fossil animals representing basal lineages include Puijila, of the Early Miocene in Arctic Canada. It resembled a modern otter, but shows evidence of quadrupedal swimming—retaining a form of aquatic locomotion that led to those employed by modern pinnipeds. Potamotherium, which lived in the same period in Europe, was similar to Puijila but more aquatic. The braincase of Potamotherium shows evidence that it used its whiskers to hunt, like modern seals. Both Puijila and Potamotherium fossils have been found in lake deposits, suggesting that seal ancestors were originally adapted for fresh water. A closer relative of extant pinnipeds was Pteronarctos, which lived in Oregon 19–15 mya. As in modern seals, the maxilla or upper jaw bone of Pteroarctos intersects with the orbital wall. The extinct family Desmatophocidae lived 23–10 mya in the North Pacific. They had long skulls that with large orbits, interlocked zygomatic bones and rounded molars and premolars. They also were sexually dimorphic and may have been capable of swimming with both or either pair of flippers. Phocids are known to have existed for at least 15 million years, The mammary glands and genitals can withdraw into the body. Several species have male-biased sexual dimorphism that depends on how polygynous a species is: highly polygynous species like elephant seals are extremely sexually dimorphic, while less polygynous species have males and females that are closer in size, or, in the case of Antarctic seals, females are moderately bigger. Males of sexually dimorphic species also tend to have secondary sex characteristics, such as larger or more prominent heads, necks, chests, crests, noses/proboscises and canine teeth as well as thicker fur and manes. Though more polygynous species tend to be sexually dimorphic, some evidence suggests that size differences between the sexes originated due to ecological differences, with polygyny developing later.
thumb|upright=0.8|Male and female [[South American sea lions, showing sexual dimorphism]]
Almost all pinnipeds have fur coats, the exception being the walrus, which is only sparsely covered. Even some fully furred species (particularly sea lions) are less furry than land mammals. Fur seals have lush coats consisting of an undercoat and guard hairs. In species that live on ice, young pups have thicker coats than adults. The individual hairs on the coat, known collectively as lanugo, can trap heat from sunlight and keep the pup warm. Pinnipeds are typically countershaded, and are darker colored dorsally and lighter colored ventrally, which serves to counter the effects of self-shadowing caused by light shining over the ocean water. The pure white fur of harp seal pups conceals them in their Arctic environment. Several species have clashing patterns of light and dark pigmentation. Pinnipeds have several adaptions for reducing drag. In addition to their streamlined bodies, they have smooth networks of muscle bundles in their skin that may increase laminar flow and cut through the water. The hair erector muscles are absent, so their fur can be streamlined as they swim.
When swimming, otariids rely on their fore-flippers for locomotion in a wing-like manner similar to penguins and sea turtles. Fore-flipper movement is not continuous, and the animal glides between each stroke. Compared to terrestrial carnivorans, the fore-limb bones of otariids are reduced in length, giving them less resistance at the elbow joint as the flippers flap; the hind-flippers maneuver them. Phocids and walruses swim by moving their hind-flippers and lower body from side to side, while their fore-flippers are mainly used for maneuvering. Otariids create momentum by laterally swaying their heads and necks. Seals are able to see in relative darkness with a tapetum lucidum, a reflecting layer that increases sensitivity by reflecting light back through the rods.
thumb|left|Frontal view of [[Cape fur seal head]]
On land, pinnipeds are near-sighted in dim light. This is reduced in bright light as the contracted pupil decreases the ability of the lens and the cornea to refract (bend) light. Polar living seals like the harp seal have corneas that can withstand the bright light that reflects off snow and ice, which would otherwise cause snow blindness. Color vision requires at least two types of visual pigments with different spectral sensitivities but since pinnipeds lack short-wavelength-sensitive cone cells, they are generally considered to be color-blind. Flexible eye movement has been documented in seals. The walrus can project its eyes out from its sockets in both a forward and upward direction due to its advanced extraocular muscles and absence of an orbital roof. The seal eye is durable as the corneal epithelium is hardened by keratin, and the sclera is thick enough to withstand the pressures of diving. Seals also secrete mucus from the lacrimal gland to protect their eyes. As in many mammals and birds, pinnipeds possess nictitating membranes.
The pinniped ear is adapted for hearing underwater, where it can hear sound frequencies of up to 70,000 Hz. In air, hearing is somewhat reduced in pinnipeds compared to many terrestrial mammals. While their airborne hearing sensitivity is generally weaker than humans', they still have a wide frequency range. One study of three species—the harbor seal, California sea lion and northern elephant seal—found that the sea lion was best adapted for airborne hearing, the elephant seal for underwater hearing and the harbor seal was equally adapted for both. Although pinnipeds have a fairly good sense of smell on land, it is useless under water as their nostrils are closed.
thumb|right|[[Vibrissae of walrus|alt=Photo of walrus head in profile showing one eye, nose, tusks, and "mustache"]]
The whiskers (vibrissae) are normally smooth in otariids and walruses, while those of most phocids are wavey. The whiskers of some otariids grow quite long—those of the Antarctic fur seal can reach – while walruses have the most vibrissae, at 600–700 individual hairs. Compared to terrestrial mammals, the vibrissae of pinnipeds have ten times more nerve connections, allowing them to effectively detect vibrations in the water. These vibrations are generated, for example, when a fish swims through water. Detecting vibrations is useful when the animals are foraging, and may add to or even replace vision, particularly in darkness.
Harbor seals can follow hydrodynamic paths made minutes earlier, similar to a dog following a scent trail, and can even discriminate the size and type of object responsible for the trail. Unlike terrestrial mammals, such as rodents, pinnipeds do not sweep their whiskers over an object when examining it, but can protract the hairs forward while holding them steady, maximizing their detection. The vibrissa's angle relative to the flow seems to be the most important contributor to detection ability. The middle ear contains sinuses that probably fill with blood during dives, preventing middle ear squeeze.
The circulatory system of pinnipeds is large and elaborate; retia mirabilia line the inside of the trunk and limbs, allowing for greater oxygen storage during diving. As with other diving mammals, pinnipeds have large amounts of hemoglobin and myoglobin stored in their blood and muscles respectively. This provides enough oxygen storage for them to stay submerged for long periods. Deep-diving species such as elephant seals have blood volumes that represent up to 20% of their body weight. When diving, they reduce their heart rate, and blood flow is mostly restricted to the heart, brain and lungs.
Thermoregulation
thumb|right|Northern elephant seal resting in water
Pinnipeds keep warm by having large, thick bodies, insulating blubber and fur, and fast metabolism. Their idle body temperature is around against the ocean water. Metabolic rates of different species vary between 1.5 and 3 times that of land mammals. Also, the blood vessels in their flippers are adapted for countercurrent exchange; small veins surround arteries transporting blood from the body core, capturing heat from them. While blubber and fur keep the seal warm in water, they can also overheat the animal when it is on land. To counteract overheating, many species cool off by covering themselves in sand. Monk seals may even dig up the cooler layers. The northern fur seal cools off by panting.
Sleep
Pinnipeds spend many months at a time at sea, so they must sleep in the water. Scientists have recorded elephant seals sleeping for minutes at a time while slowly drifting downward in a belly-up orientation.
Distribution and habitat
thumb|right|Walrus on ice off Alaska. This species has a discontinuous distribution around the [[Arctic Circle.]]
Living pinnipeds are widespread in cold oceanic waters; particularly in the North Atlantic, the North Pacific and the Southern Ocean. By contrast, the consistently warm Indomalayan waters have no seals. Monk seals and some otariids live in tropical and subtropical waters. Seals usually require cool, nutrient-rich waters with temperatures lower than . Even in more tropical climates, lower temperatures and biological productivity may be provided by currents. In polar regions, seals haul out on to both fast ice and drift ice. Some even den underneath the ice, particularly in pressure ridges and crevasses.
Behavior and life history
thumb|right|Cape fur seals in water and at haulout
Pinnipeds have an amphibious lifestyle; they are mostly aquatic, but haul out to breed, molt, rest, sun or to avoid aquatic predators. Several species are known to migrate over vast distances, particularly in response to environmental changes. Elephant seals are at sea for most of the year and there are vast distances between their breeding and molting sites. The northern elephant seal is one of farthest mammalian migraters, traveling . Otariids tend to migrate less than phocids, especially tropical species. Traveling seals may reach their destination using geomagnetic fields, water and wind currents, solar and lunar positions and the temperature and chemical makeup of the water.
Pinnipeds may dive during foraging or to avoid predators. When foraging, for example, the Weddell seal typically dives for no more than 15 minutes and deep, but can dive for as long as 73 minutes and reach deep. Northern elephant seals often dive for as long as 20 minutes. They can also dive and for over an hour. The dives of otariids tend to be shorter and less deep. They typically last 5–7 minutes with average depths to . However, the New Zealand sea lion has been recorded diving to a maximum of and have submerged for as long as 12 minutes. The diet of walruses does not require them to dive very deep or very long. Pinnipeds generally live 25–30 years.
Foraging and predation
thumb|left|[[Steller sea lion capturing a white sturgeon]]
All pinnipeds are carnivorous and predatory. As a whole, they mostly feed on fish and cephalopods, but also consume crustaceans, bivalves, zooplankton and endothermic (warm-blooded) prey like sea birds. While most species have generalist diets, a few are specialists. Examples are krill-eating crabeater seals, crustacean-eating ringed seals, squid specialists like the Ross seal and southern elephant seal, and the bearded seal and walrus, which specialize on benthic invertebrates. The leopard seal, a prolific predator of penguins, is known to violently shake its prey to death. Complex serrations in the teeth of filter-feeding species, such as crabeater seals, allow water to leak out as they swallow their planktonic food.
thumb|left|[[Orca hunting a Weddell seal]]
Pinnipeds lessen the chance of predation by gathering in groups. Some species are capable of inflicting damaging wounds on their attackers with their sharp canines; adult walruses are particularly risky prey for polar bears. When out at sea, northern elephant seals dive out of the reach of surface-hunting orcas and white sharks. In the Antarctic, which lacks terrestrial predators, pinniped species spend more time on the ice than their Arctic counterparts.
Interspecific predation among pinnipeds does occur. The leopard seal is known to prey on many other species, especially the crabeater seal. Leopard seals typically target crabeater pups, particularly from November to January. Older crabeater seals commonly bear scars from failed leopard seal attacks; a 1977 study found that 75% of a sample of 85 individual crabeaters had these scars. Walruses, despite being specialized for feeding on bottom-dwelling invertebrates, occasionally prey on Arctic seals. They kill their prey with their long tusks and eat their blubber and skin. Steller sea lions have been recorded eating harbor seals, northern fur seals and California sea lions, particularly pups and small adults. New Zealand sea lions feed on pups of some fur seal species, and the South American sea lion may prey on South American fur seals.
Reproductive behavior
thumb|Harbor seals on sandy beach. This species breeds on land but mates in the water.
The mating system of pinnipeds varies from extreme polygyny to serial monogamy. Species that breed on land are usually more polygynous, as females gather in large aggregations and males are able to mate with them as well as defend them from rivals. These species include elephant seals, grey seals and most otariids. and some may be fully or partially underwater. Males defend their territorial boundaries with threatening vocalizations and postures, but physical fights are usually not very violent, and are mostly limited to early in the season. Individuals also return to the same territorial site each breeding season. In certain species, like the Steller sea lion and northern fur seal, a dominant male can maintain a territory for as long as 2–3 months. Females can usually move freely between territories and males are unable to coerce females who are intent on leaving, but in some species such as the northern fur seal, South American sea lion and Australian sea lion, males keep females in their territories with threatening displays and even violence. In some phocid species, like the harbor seal, Weddell seal and bearded seal, the males establish "maritories" and patrol and defend the waters bordering female haul-out areas, waiting for a female to enter. In some species, including elephant seals, grey seals and non-lekking walruses, males will try to lay claim to the desired females and defend them from rivals. Elephant seal males, in particular, establish dominance hierarchies via displays and fights, with the highest ranking males having a near monopoly on reproductive success. Grey seal males usually place themselves among a cluster of females whose members may change over time, while males of some walrus populations guard female herds.
Younger or subdominant male pinnipeds may attempt to achieve reproductive success in other ways including sneakiness, harassment of departing females or even group raids. Female pinnipeds do appear to have some choice in mates, particularly in lek-breeding species like the walrus, but also in elephant seals where the males try to dominate all the females that they want to mate with. When a female elephant seal or grey seal is mounted by an unwanted male, she tries to resist and get away. This commotion attracts other males to the scene, and the most dominant will take over and mate with female himself. Dominant female elephant seals stay in the center of the colony where they are in the domain of a more dominant male, while marginal females are left with subordinates. Female Steller sea lions may solicit their territorial males for mating.
Birth and parenting
thumb|left|Harbor seal mother nursing pup
Otariids enter estrus shortly after giving birth, while phocids can mate again during late lactation or when their young are weaned and walruses have five- to six-year gaps between births. All species have delayed implantation, in which the embryo does not enter the uterus for weeks or months. Delayed implantation allows the female to wait until conditions are right for birthing. Gestation in seals (including delayed implantation) typically lasts a year. For most species, birthing takes place in spring and summer. Usually, single pups are born; twins are rare and have high mortality rates. Pups of most species are born relatively developed and precocial.
Pinniped milk has "little to no lactose". Mother pinnipeds have different strategies for maternal care and lactation. Phocids such as elephant seals, grey seals and hooded seals have a lactation period that lasts days or weeks, during which they fast and nurse their pups on land or ice. The milk of these species consists of up to 60% fat, allowing the young to grow quickly. Each day until they are weaned, northern elephant seal pups gain . Some pups gain weight more quickly than others by stealing extra milk from other mothers. Alloparenting occurs in these fasting species; while most northern elephant seal mothers nurse their own pups and reject nursings from alien pups, some do accept alien pups with their own.
thumb|right|Mother walrus with calf
For otariids and some phocids like the harbor seal, mothers fast and nurse their pups for a few days at a time. In between nursing bouts, the females forage at sea while the young stay behind onshore. If there is enough food close to shore, a female can be gone for as little as a day, but otherwise may be at sea for as long as three weeks. Lactation in otariids may last 6–11 months; in the Galápagos fur seal it can last up to three years. Pups of these species are weaned at heavier weights than their phocid counterparts, but the latter grow quicker. Walruses are unique in that mothers nurse their young at sea. Young pinnipeds typically start swimming on their own and some species can even swim as newborns. Young may wait days or weeks before entering the water; elephant seals start swimming weeks after weaning.
Male pinnipeds generally play little role in raising the young. Males can also pose threats to the safety of pups, particularly during fights. Pups of some species may be abducted, assaulted and killed by males, possibly due to sexual frustration.
Communication
thumb|right|Vocalization of female [[Antarctic fur seal]]
Pinnipeds can produce a number of vocalizations. While most vocals are audible to the human ear, In addition, the vocals of northern elephant seals may produce infrasonic vibrations. Vocals are produced both in air and underwater; the former are more common among otariids and the latter among phocids. Antarctic seals are noisier on land or ice than Arctic seals due to the absence of polar bears. Male vocals are usually deeper than those of the females. Vocalizations are particularly important during the breeding seasons. Dominant male elephant seals display their status and power with "clap-threats" and loud drum-like calls that may be modified by the proboscis. Male otariids have strong barks, growls and roars. Male walruses are known to produce gong-like calls when attempting to attract females, these are amplified underwater with inflatable throat sacs.
The Weddell seal has perhaps the most extensive vocal repertoire, producing both airborne and underwater sounds. Trilling, gluping, chirping, chugging and knocking are some examples of the calls produced underwater. When warning other seals, the calls may be pronounced by "prefixes" and "suffixes". Similar calls have been recorded in other Antarctic seals and in bearded seals. In some pinniped species, there appear to be regional dialects or even individual variations in vocalizations. These differences are likely important for territorial males recognizing their neighbors and mothers and pups who need to remain in contact on crowded beaches. Female seals emit a "pulsed, bawling" contact call, while pups respond by squawking. Contact calls are particularly important for otariid mothers returning from sea. Other vocalizations produced by seals include grunts, rasps, rattles, creaks, warbles, clicks and whistles. They demonstrate the ability to understand simple syntax and commands when taught an artificial sign language, though they only rarely used the signs semantically or logically. In 2011, a captive California sea lion named Ronan was recorded bobbing its head in synchrony to musical rhythms. This "rhythmic entrainment" was previously seen only in humans, parrots and other birds possessing vocal mimicry. Harbor seals have been found to adapt quickly when presented with changes to stimuli in regards to rewards and non-rewards. Adult male elephant seals can recognize each other's vocalizations by remembering the rhythm and timbre. In the 1970s, a captive harbor seal named Hoover was trained to imitate human speech and laughter.
For sea lions used in entertainment, trainers toss a ball at the animal or simply place the object on its nose, so it will eventually understand the behavior desired. A sea lion may need a year of training before it can publicly perform. Its long-term memory allows it to perform a trick after as much as three months of non-performance. In Inuit mythology, they are associated with the goddess Sedna, who sometimes transformed into a seal. It was believed that marine mammals, including seals, came from her severed fingers. In modern culture, pinnipeds are thought of as cute, playful and comical figures.
In captivity
Pinnipeds can be found in facilities around the world, as their size and playfulness make them popular attractions. Some organizations, such as the Humane Society of the United States and World Animal Protection, object to keeping marine mammals in captivity. They state that the exhibits could not be large enough to house animals that have evolved to be migratory, and a pool could never replace the size and biodiversity of the ocean. They also state that the tricks performed for audiences are "exaggerated variations of their natural behaviors" and distract the people from the animal's unnatural environment.
California sea lions are used in military applications by the U.S. Navy Marine Mammal Program, including detecting naval mines and enemy divers. In the Persian Gulf, the animals have been trained to swim behind divers approaching a U.S. naval ship and attach a clamp with a rope to the diver's leg. Navy officials say that the sea lions can do this in seconds, before the enemy realizes what happened. Organizations like PETA believe that such operations put the animals in danger. The Navy insists that the sea lions are removed once their job is done.
Hunting
thumb|upright=1.1|Men killing northern fur seals on [[St. Paul, Alaska|Saint Paul Island, Alaska, in the mid-1890s.]]
Humans have hunted seals since the Stone Age. Originally, seals were merely hit with clubs during haul-out. Eventually, more lethal weapons were used, like spears and harpoons. They were also trapped in nets. The use of firearms in seal hunting during the modern era drastically increased the number of killings. Pinnipeds are typically hunted for their meat and blubber. The skins of fur seals and phocids are made into coats, and the tusks of walruses have been used as ivory. There is a distinction made between the subsistence hunting of seals by indigenous peoples of the Arctic and commercial hunting: subsistence hunters depend on seal products for survival. National and international authorities have given special treatment to aboriginal hunters since their methods of killing are seen as more sustainable and smaller in scope. However indigenous people have recently used more modern technology and are profiting more from seal products in the marketplace. Some anthropologists argue that the term "subsistence" should also apply to these activities, as long as they are local in scale. More than 100,000 phocids (especially ringed seals) as well as around 10,000 walruses are harvested annually by native hunters. Several species that were commercially exploited have rebounded in numbers; for example, Antarctic fur seals may have reached their pre-harvesting numbers. The northern elephant seal nearly went extinct in the late 19th century, with only a small population remaining on Guadalupe Island. It has since recolonized much of its historic range, but has a population bottleneck. Conversely, the Mediterranean monk seal was extirpated from much of the Mediterranean and its current range is still limited.
Several species of pinniped continue to be exploited. The Convention for the Conservation of Antarctic Seals protects species within the Antarctic and surrounding waters, but allows restricted hunting of crabeater seals, leopard seals and Weddell seals. Weddell seal hunting is forbidden between September and February if the animal is older than a year, to ensure healthy population growth. The Government of Canada permits the hunting of harp seals. This has been met with controversy and debate. Proponents of seal hunts insist that the animals are killed humanely and the white-coated pups are not taken, while opponents argue that it is irresponsible to kill harp seals as they are already threatened by declining habitat.
The Caribbean monk seal has been killed and exploited by European settlers and their descendants since 1494, starting with Christopher Columbus himself. The seals were easy targets for organized sealers, fishermen, turtle hunters and buccaneers because they evolved with little pressure from terrestrial predators and were thus "genetically tame". In the Bahamas, as many as 100 seals were slaughtered in one night. The species was considered to be already extinct by the mid-nineteenth century until a small colony was found near the Yucatán Peninsula in 1866. Seal killings continued, and the last reliable report of the animal alive was in 1952 at Serranilla Bank. The IUCN declared it extinct in 1996. The Japanese sea lion was common around the Japanese islands, but overexploitation and competition from fisheries drastically decreased the population in the 1930s. The last recorded individual was a juvenile in 1974.
Conservation issues
thumb|right|Harp seal pup. This ice-living species is vulnerable to the effects of climate change
As of 2021, the International Union for Conservation of Nature (IUCN) recognizes 36 pinniped species. With the Japanese sea lion and the Caribbean monk seal recently extinct, ten more are considered at risk. They are ranked as:
- "Endangered": Hawaiian monk seal, Mediterranean monk seal, Galápagos fur seal, Australian sea lion, New Zealand sea lion, Caspian seal, and Galápagos sea lion.
- "Vulnerable": northern fur seal, hooded seal, and walrus.
Pinnipeds face various threats. They are unintentionally caught in fishing nets by commercial fisheries and accidentally swallow fishing hooks. Gillnetting and seine netting is a significant cause of mortality in seals and other marine mammals. Species commonly entangled include California sea lions, Hawaiian monk seals, northern fur seals and Cape fur seals. Pinnipeds are also affected by marine pollution. Organic chemicals tend to accumulate in these animals since they are high in the food chain and have large reserves of blubber. Lactating mothers can pass the toxins on to their young. These pollutants can cause gastrointestinal cancers, and decreased fertility and immunity to infectious diseases. Other man-made threats include habitat destruction by oil and gas exploitation, encroachment by boats, and underwater noise.
thumb|upright|[[Grey seal on beach occupied by humans near Niechorze, Poland. Pinnipeds and humans may compete for space and resources.]]
Species that live in polar habitats are vulnerable to the effects of climate change on oceans, particularly declines in sea ice. In 2010 and 2011, sea ice in the Northwest Atlantic was at or near an all-time low and harp seals as well as ringed seals that bred on thin ice saw increased death rates. In the Antarctic, the decreased duration and extent of the sea ice and nutrient availability could potentially reduce the survival of Weddell seal pups and may have important implications for population growth rates. Antarctic fur seals in South Georgia in the South Atlantic saw major decreases over a 20-year study, during which scientists measured increased sea surface temperature anomalies.
Some species have become so numerous that they conflict with local people. In the United States, pinnipeds are protected under the Marine Mammal Protection Act of 1972 (MMPA). Since that year, California sea lion populations have risen to 250,000. These animals began exploiting more man-made environments, like docks, for haul-out sites. Many docks are not designed to withstand the weight of several resting sea lions. Wildlife managers have used various methods to control the animals, and some city officials have redesigned docks so they can better resist sea lion use. Inland-living New Zealand sea lions face unique human conflicts such as road mortality and run-ins with human infrastructure. Seals also conflict with fisheries; a 2024 metastudy found that globally pinnipeds affected over 33 percent of fishing days and stole over 13 percent of catches. In 2007, MMPA was amended to permit the lethal removal of sea lions from salmon runs at Bonneville Dam. In the 1980s and 1990s, South African politicians and fishermen demanded that brown fur seals be culled, believing that the animals competed with commercial fisheries. Scientific studies found that culling fur seals would actually have a negative effect on the fishing industry, and the culling option was dropped in 1993.
Population monitoring methods for pinnipeds increasingly include aerial imagery and automated image-processing workflows, which can support repeated surveys of colonies and haul-out sites.
Notes
==References==<!-- BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY 279:32 -->