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Earless seal
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Earless seal
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Earless seals[2]
Temporal range: Aquitanian–present Early Miocene – Holocene, possible late Oligocene record[1]
Harbor seal, Phoca vitulina
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Superfamily: Phocoidea
Family: Phocidae
Gray, 1821
Type genus
Phoca
Linnaeus, 1758
Subfamilies

The earless seals, phocids, or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae (/ˈfoʊsɪdiː/). They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae. Seals live in the oceans of both hemispheres and, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

Taxonomy and evolution

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Evolution

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Fossil Pliophoca skull

The earliest known fossil earless seal is Noriphoca gaudini from the late Oligocene or earliest Miocene (Aquitanian) of Italy.[1] Other early fossil phocids date from the mid-Miocene, 15 million years ago in the north Atlantic.[1][3] Until recently, many researchers believed that phocids evolved separately from otariids and odobenids; and that they evolved from otter-like animals, such as Potamotherium, which inhabited European freshwater lakes. Recent evidence strongly suggests a monophyletic origin for all pinnipeds from a single ancestor, possibly Enaliarctos, most closely related to the mustelids and bears.[4]

Monk seals and elephant seals were previously believed to have first entered the Pacific through the open straits between North and South America,[5] with the Antarctic true seals either using the same route or travelled down the west coast of Africa.[6] It is now thought that the monk seals, elephant seals, and Antarctic seals all evolved in the southern hemisphere, and likely dispersed to their current distributions from more southern latitudes.[7]

Taxonomy

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Pinnipedia
Cladogram showing relationships among the phocids, combining several phylogenetic analyses.[8]

In the 1980s and 1990s, morphological phylogenetic analysis of the phocids led to new conclusions about the interrelatedness of the various genera. More recent molecular phylogenetic analyses have confirmed the monophyly of the two phocid subfamilies (Phocinae and Monachinae).[9][10][11][5] The Monachinae (known as the "southern" seals), is composed of three tribes; the Lobodontini, Miroungini, and Monachini. The four Antarctic genera Hydrurga, Leptonychotes, Lobodon, and Ommatophoca are part of the tribe Lobodontini. Tribe Miroungini is composed of the elephant seals. The Monk seals (Monachus and Neomonachus) are all part of the tribe Monachini.[12] Likewise, subfamily Phocinae (the "northern" seals) also includes three tribes; Erignathini (Erignathus), Cystophorini (Cystophora), and Phocini (all other phocines). More recently, five species have been split off from Phoca, forming three additional genera.[13]

Alternatively the three monachine tribes have been evaluated to familiar status, which elephant seals and the Antarctic seals are more closely related to the phocines.[14]

Extant genera

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Subfamily Tribe Image Genus species
Subfamily Monachinae Tribe Monachini Monachus Fleming, 1822
Neomonachus Slater & Helgen, 2014
Tribe Miroungini Mirounga Gray, 1827
Tribe Lobodontini Ommatophoca Gray, 1844
Lobodon Gray, 1844
Hydrurga Gistel, 1848
Leptonychotes Gill, 1872
Subfamily Phocinae Tribe Cystophorini Cystophora Nilsson, 1820
Tribe Erignathini Erignathus Gill, 1866
Tribe Phocini Phoca Linnaeus, 1758
Pusa Scopoli, 1771
Pagophilus Gray, 1844
  • Harp seal, Pagophilus groenlandicus (formerly Phoca groenlandica)
Histriophoca Gill, 1873
  • Ribbon seal, Histriophoca fasciata (formerly Phoca fasciata)
Halichoerus Nilsson, 1820

Biology

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External anatomy

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Skeletal anatomy of a harbor seal. 1. Skull. 2. Spine. 3. Tail. 4. Hindlimb. 5. Forelimb. 6. Shoulder. 7. Pelvis. 8. Rib cage.
Harbor seal skull (Phoca vitulina)

Adult phocids vary from 1.17 m (3.8 ft) in length and 45 kg (99 lb) in weight in the ringed seal to 5.8 m (19 ft) and 4,000 kg (8,800 lb) in the southern elephant seal, which is the largest member of the order Carnivora. Phocids have fewer teeth than land-based members of the Carnivora, although they retain powerful canines. Some species lack molars altogether. The dental formula is: 2–3.1.4.0–21–2.1.4.0–2

While otariids are known for speed and maneuverability, phocids are known for efficient, economical movement. This allows most phocids to forage far from land to exploit prey resources, while otariids are tied to rich upwelling zones close to breeding sites. Phocids swim by sideways movements of their bodies, using their hind flippers to fullest effect.[15] Their fore flippers are used primarily for steering, while their hind flippers are bound to the pelvis in such a way that they cannot bring them under their bodies to walk on them. They are more streamlined than fur seals and sea lions, so they can swim more effectively over long distances. However, because they cannot turn their hind flippers downward, they are very clumsy on land, having to wriggle with their front flippers and abdominal muscles.

Seal kidney

Phocid respiratory and circulatory systems are adapted to allow diving to considerable depths, and they can spend a long time underwater between breaths. Air is forced from the lungs during a dive and into the upper respiratory passages, where gases cannot easily be absorbed into the bloodstream. This helps protect the seal from the bends. The middle ear is also lined with blood sinuses that inflate during diving, helping to maintain a constant pressure.[15]

Phocids are more specialized for aquatic life than otariids. They lack external ears and have sleek, streamlined bodies. Retractable nipples, internal testicles,[16] and an internal penile sheath provide further streamlining. A smooth layer of blubber lies underneath the skin. Phocids are able to divert blood flow to this layer to help control their temperatures.[17]

Communication

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Unlike otariids, phocine seals do not communicate by "barking". Instead, they communicate by slapping the water and grunting, with a few species have been documented to clap at each other underwater.[18] One study published in Animal Behaviour found that seals use rhythmic percussive signalling (clapping) in both "agonistic interactions" and display behavior.[19]

Conversely, monachine seals are well known to vocalize: elephant seals often vocalize on land,[clarification needed] with the bulls being well known for roaring to establish dominance and identifying themselves.[20] The Weddell and leopard seals are well known for their underwater singing.[21][22][23][24]

Movements

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With short front flippers and because their rear flipper is unable to rotate, true seals cannot walk when out of the water like sea lions. As a result, they bounce themselves forward in a motion called galumphing;[25][26] the polar explorer Edward Wilson referred to the motion as lolloping.[27]

Reproduction

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Photo of seven adult and juvenile southern elephant seals packed closely on beach
Southern elephant seals in Argentina
Living only in Lake Saimaa, Finland, Saimaa ringed seals, a subspecies of ringed seal, are among the most endangered seals in the world, having a total population of only about 400 individuals.[28]

Phocids spend most of their time at sea, although they return to land or pack ice to breed and give birth. Pregnant females spend long periods foraging at sea, building up fat reserves, and then return to the breeding site to use their stored energy to nurse pups. However, the common seal displays a reproductive strategy similar to that used by otariids, in which the mother makes short foraging trips between nursing bouts.[citation needed]

Because a phocid mother's feeding grounds are often hundreds of kilometers from the breeding site, she must fast while lactating. This combination of fasting with lactation requires the mother to provide large amounts of energy to her pup at a time when she is not eating (and often, not drinking). Mothers must supply their own metabolic needs while nursing. This is a miniature version of the humpback whales' strategy, which involves fasting during their months-long migration from arctic feeding areas to tropical breeding/nursing areas and back.[citation needed]

Phocids produce thick, fat-rich milk that allows them to provide their pups with large amounts of energy in a short period. This allows the mother to return to the sea in time to replenish her reserves. Lactation ranges from five to seven weeks in the monk seal to just three to five days in the hooded seal. The mother ends nursing by leaving her pup at the breeding site to search for food (pups continue to nurse if given the opportunity). "Milk stealers" that suckle from unrelated, sleeping females are not uncommon; this often results in the death of the mother's pup, since a female can only feed one pup.[citation needed]

Growth and maturation

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The pup's diet is so high in calories that it builds up a fat store. Before the pup is ready to forage, the mother abandons it, and the pup consumes its own fat for weeks or even months while it matures. Seals, like all marine mammals, need time to develop the oxygen stores, swimming muscles, and neural pathways necessary for effective diving and foraging. Seal pups typically eat no food and drink no water during the period, although some polar species eat snow. The postweaning fast ranges from two weeks in the hooded seal to 9–12 weeks in the northern elephant seal.[29] The physiological and behavioral adaptations that allow phocid pups to endure these remarkable fasts, which are among the longest for any mammal, remain an area of active study and research.

Feeding strategy

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Phocids make use of at least four different feeding strategies: suction feeding, grip and tear feeding, filter feeding, and pierce feeding. Each of these feeding strategies is aided by a specialized skull, mandible, and tooth morphology. However, despite morphological specialization, most phocids are opportunistic and employ multiple strategies to capture and eat prey. For example, the leopard seal, Hydrurga leptonyx, uses grip and tear feeding to prey on penguins, suction feeding to consume small fish, and filter feeding to catch krill.[30]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Earless seal

View on Grokipedia
from Grokipedia
Earless seals, scientifically known as the Phocidae, are a diverse group of 18 species within the lineage, distinguished by the absence of external flaps and reliance on small ear holes for hearing. These "true seals" possess streamlined, torpedo-shaped bodies covered in for insulation and buoyancy, short foreflippers for steering, and powerful hind flippers that extend backward for efficient propulsion through water, enabling dives to depths exceeding 500 meters in some species. On land, they move awkwardly by undulating their bodies and using foreflippers to pull forward, often resting in large colonies on beaches or ice floes. Phocidae is divided into two primary subfamilies: (northern seals, including harbor, gray, and ringed seals) and (southern and monk seals, such as elephant seals and the critically endangered Hawaiian monk seal), reflecting their biogeographic patterns with species broadly distributed along temperate to polar coastlines above 30°N and below 50°S . These seals are obligate carnivores, preying mainly on , , crustaceans, and occasionally seabirds or other pinnipeds, with feeding strategies varying from suction feeding in deep divers to grip-and-tear in surface hunters. Reproduction typically involves polygynous systems where males defend territories, with periods of 9–12 months often featuring delayed implantation; pups are born precocial, covered in fur, and nursed on high-fat for rapid growth before early . Notable for their ecological roles in marine food webs as both predators and prey, earless seals face threats from , which reduces habitats for and species, as well as in fisheries and historical overhunting that led to population declines in species like the . Conservation efforts, including protected areas and international agreements like the Convention on Migratory Species, have supported recoveries in some populations, highlighting the family's resilience and importance to .

Taxonomy

Evolutionary history

The earless seals (Phocidae) trace their origins to the late –early transition, approximately 27–20 million years ago, evolving from terrestrial arctoid carnivorans within the suborder , most closely related to musteloid lineages such as mustelids. This period marked the initial divergence of Phocidae from the common ancestor shared with Otariidae (eared seals) and (walruses), establishing the monophyletic clade Pinnipedia as a whole. Fossil evidence indicates that early phocids arose in the North Atlantic or (ancient Mediterranean) region, with the crown group Phocidae emerging around 27 million years ago. Key fossil records provide insights into primitive phocids, such as Noriphoca from the early (~22 million years ago) in , representing one of the earliest definitive members of the family, and Leptophoca from the early of the North Pacific, showcasing transitional aquatic features. These fossils highlight in pinnipeds, where phocids independently developed aquatic adaptations like the loss of external ears, a streamlined body form, and hind limb modifications for propulsion, paralleling but distinct from those in otariids. Middle taxa, including Monotherium from the North Atlantic and Prophoca from the eastern North Atlantic, further illustrate this early diversification, with anatomical traits indicating semi-aquatic lifestyles. Major adaptive radiations occurred during the (5.3–2.6 million years ago), as phocids expanded globally and refined traits for , including the of thick blubber layers for in cold waters and enhanced physiological adaptations for prolonged diving, such as increased in blood and muscles. These developments facilitated the emergence of modern phocid forms, enabling occupation of diverse habitats from polar ice to temperate coasts. Within Pinnipedia, Phocidae forms a monophyletic group distinct from the clade (Otariidae + ), supported by shared derived traits like the absence of external ear flaps and specialized cranial features for underwater hearing. Phylogenetic analyses confirm this separation, with Phocidae branching off early in pinniped evolution, underscoring their independent trajectory toward true seal morphology.

Classification

Earless seals, also known as true seals, are classified within the order , suborder , infraorder Pinnipedia, and family Phocidae. The family Phocidae is divided into two main subfamilies: , which includes northern hemisphere species often referred to as northern seals, and , comprising southern hemisphere species known as southern seals or monk seals. The taxonomic framework for Phocidae was established in the by British zoologist , who formally described the family in 1821 based on morphological characteristics. Subsequent revisions in the refined subfamily boundaries, but modern , utilizing complete coding regions, has confirmed the monophyly of Phocidae as well as the distinct clades of and . Key diagnostic traits distinguishing Phocidae from other pinnipeds include the absence of external ear pinnae, the inability to rotate hind flippers forward under the body for terrestrial locomotion, and a typical dental formula of I 3/2, C 1/1, P 4/4, M 1/1 (totaling 34 teeth), with upper incisors featuring simple, pointed crowns and postcanine teeth adapted for grasping prey. These features underscore their classification as "earless" seals, in contrast to eared seals (family Otariidae), which possess visible ear flaps and rotatable hind flippers. The name Phocidae originates from the type genus Phoca, derived from the Ancient Greek word phōkē (φώκη), meaning "seal," reflecting the family's core identity as true seals. This nomenclature highlights their distinction from eared seals and walruses within Pinnipedia, emphasizing the earless morphology as a defining characteristic.

Diversity

The family Phocidae encompasses 18 extant species distributed across two subfamilies: Phocinae in the Northern Hemisphere and Monachinae primarily in the Southern Hemisphere. The subfamily Phocinae includes 10 species adapted to Arctic and subarctic environments, such as the harbor seal (Phoca vitulina), which inhabits temperate to polar coastal waters of the North Atlantic and Pacific, and the ringed seal (Pusa hispida), a key prey species for polar bears widely distributed across the Arctic Ocean. Other notable Phocinae species are the spotted seal (Phoca largha), Baikal seal (Pusa sibirica), Caspian seal (Pusa caspica), ribbon seal (Histriophoca fasciata), harp seal (Pagophilus groenlandicus), hooded seal (Cystophora cristata), bearded seal (Erignathus barbatus), and grey seal (Halichoerus grypus). In contrast, the subfamily comprises 8 , many of which are specialists or occur in temperate to tropical regions. Examples include the elephant seals of the genus Mirounga, with the (M. angustirostris) endemic to the eastern North Pacific and the (M. leonina) breeding on islands. The genus Hydrurga is monotypic, consisting of the leopard seal (H. leptonyx), an in pack ice known for its serpentine body and diverse diet including and other seals. Similarly, the genus Leptonychotes includes only the (L. weddellii), a deep-diving that reaches depths exceeding 600 meters in coastal areas and is distinguished by its robust build and lack of external ear openings. Recent taxonomic revisions have refined the classification within . In 2014, phylogenetic analysis of and skull morphology separated the (Neomonachus schauinslandi) and the extinct (N. tropicalis) into the distinct genus Neomonachus, distinguishing them from the (Monachus monachus) based on genetic divergence dating back millions of years. Ongoing debates persist regarding the (Pusa caspica), with some genetic studies suggesting close affinity to the , potentially warranting status (P. hispida ssp. caspica), though it is currently recognized as a full species endemic to the . Patterns of among earless seals underscore their polar affinities, with over 80% of confined to high-latitude habitats like the , , and islands, where they exploit ice-associated niches for breeding and foraging. Notable exceptions include the tropical monk seals, such as the critically endangered Hawaiian and Mediterranean species, which represent populations in warmer, isolated oceanic environments.

Description

Anatomy

Earless seals, or phocids, possess a streamlined body shape that minimizes hydrodynamic drag during swimming, with a tapered anterior and posterior end facilitating efficient movement through water. Their forelimbs are modified into short, paddle-like flippers used primarily for steering, while the hind flippers, which extend directly backward and cannot rotate forward under the body, provide the main propulsion through lateral undulations of the torso. Unlike some other pinnipeds, phocids lack a , further reducing resistance in their aquatic environment, and their nostrils feature valvular structures that seal tightly during submersion to prevent water ingress. Sensory systems in earless seals are finely tuned for underwater conditions. The eyes are relatively small but equipped with a , a reflective layer behind the that enhances low-light vision by redirecting photons to photoreceptors, aiding prey detection in dimly lit depths. Vibrissae, or , form a mystacial pad around the muzzle and function as hydrodynamic sensors, detecting subtle water movements and vibrations from nearby prey such as . Hearing remains acute despite the absence of external pinnae; internal ear structures, including a specialized with air sinuses, allow for and sensitivity to underwater frequencies up to several kilohertz. Internally, phocids rely on substantial physiological adaptations for prolonged submersion. A thick layer, comprising up to 30% of body mass in species like harbor seals, serves dual roles in against cold water and positive control during dives. The lungs collapse during dives at depths of about 25-50 meters, helping to mitigate nitrogen absorption and . Skeletal muscles are enriched with , an oxygen-binding protein that stores substantial reserves—up to 10 times higher than in humans—enabling aerobic and supporting dive durations of up to two hours in species like elephant seals. The skeleton of earless seals reflects their transition to an aquatic lifestyle, with reduced limb girdles and elongated phalanges forming rigid flippers for streamlined propulsion. In certain species, such as elephant seals, the are compressed, limiting neck flexibility to reduce drag while maintaining structural integrity under diving stresses. is specialized for piscivory and benthic foraging, featuring sharp, pointed incisors and canines for grasping slippery , alongside robust postcanine teeth adapted for crushing the exoskeletons of crustaceans and mollusks.

Size and variation

Earless seals, or members of the family Phocidae, exhibit a wide range in adult body size, from the smallest species, the (Pusa hispida), which measures approximately 1.5 m in length and weighs 50–100 kg, to the largest, the (Mirounga leonina), with males reaching up to 6 m in length and 4,000 kg in mass. This variation spans over an in mass across the family's 19 species, reflecting adaptations to diverse marine environments from polar to temperate waters. Sexual dimorphism in size is pronounced in some phocid species, particularly those with polygynous mating systems, such as elephant seals, where adult males are 2–3 times heavier than females due to intense male-male competition for mates. In contrast, species like the (Phoca vitulina) show minimal dimorphism, with males only about 19% heavier and 7% longer than females on average. This spectrum of dimorphism influences and reproductive strategies across the family. Ontogenetic variation is characteristic of phocids, with pups typically born at 10–20% of adult body size; for example, pups weigh around 11 kg at birth compared to adult masses of 100–200 kg. Rapid post-weaning growth occurs through nursing on with high content, up to 50% in many species, enabling pups to nearly double their mass in weeks. This strategy supports quick development in harsh environments before independent foraging begins. Intraspecific size variation exists among populations, often linked to regional prey availability; for instance, southern elephant seals (M. leonina) in waters are larger than northern elephant seals (M. angustirostris) in temperate Pacific regions, with southern males averaging heavier masses up to 3,700 kg versus 2,300 kg. Similarly, populations in northern areas attain greater asymptotic lengths (up to 149 cm for females) than those in southern subarctic regions (around 126 cm). Such differences highlight environmental influences on growth within species.

Behavior

Locomotion

Earless seals, or phocids, are adapted for efficient aquatic locomotion through undulatory , where lateral movements of the body and , combined with powerful from the hind flippers acting as hydrofoils, generate forward thrust. This pseudo-axial propulsion allows them to achieve average cruising speeds of 5 to 10 km/h, with short bursts reaching up to 35 km/h in some species during pursuits or escapes. To conserve energy during prolonged dives, they incorporate phases, particularly on descent and ascent, minimizing active swimming effort. On land, earless seals exhibit inefficient terrestrial movement, primarily through a belly-flopping motion known as galumphing or inchworm-like propulsion, where they undulate their bodies to inch forward while dragging their fore flippers. This locomotion is energetically costly and limited to short distances, typically used for hauling out on beaches or accessing breeding sites. Diving in earless seals is facilitated by specialized physiology, including the diving reflex that induces bradycardia, reducing heart rate from resting levels of around 100-120 bpm to 4-15 bpm, alongside peripheral vasoconstriction to redirect blood flow to vital organs like the brain and heart. This enables dives to depths of 500 to over 2,000 meters in some species, such as the northern elephant seal reaching up to 2,388 meters; Weddell seals typically reach up to 900 meters. Many earless seal species undertake seasonal migrations between breeding colonies and foraging grounds, covering vast oceanic distances; for instance, northern elephant seals travel approximately 19,000 to 22,500 km (12,000 to 14,000 miles) annually in round-trip journeys across the North Pacific.

Communication

Earless seals utilize a diverse array of communication modalities, including vocal, visual, and tactile signals, to facilitate interactions such as territorial defense, mating, and . These signals are adapted to both aquatic and terrestrial environments, reflecting the amphibious lifestyle of phocids. Vocalizations form a primary mode of communication in earless seals, encompassing both underwater and airborne sounds that vary by species, sex, and context. Underwater vocalizations typically range from 100 Hz to 15 kHz, with peak frequencies below 5 kHz and source levels around 130 dB re 1 μPa at 1 m, enabling long-distance transmission in . Common types include trills, clicks, and roars, which serve functions like individual recognition and coordination during foraging or social encounters. For instance, northern elephant seals (Mirounga angustirostris) produce distinctive "clap threat" calls—pulsed, low-frequency roars emitted by males during agonistic interactions on breeding grounds, with source levels reaching up to 144 dB re 1 μPa. Airborne vocalizations, such as barks and growls, are prevalent during breeding seasons and differ between sexes; males often use deeper, more resonant calls to assert dominance, while females employ higher-pitched sounds in pup interactions. These vocal patterns show species-specific and individual variation, aiding in mate attraction and rival assessment. Visual signals play a key role in close-range interactions, particularly on or , where earless seals employ posturing to convey , submission, or affiliation. Males of species like the exaggerate body size through chest inflation and rearing postures, enhancing perceived dominance during territorial disputes. Head-throwing movements, where individuals rapidly toss their heads backward, serve as displays in male-male confrontations or during pup to signal attentiveness. These behaviors are often combined with open-mouth threats to amplify visual impact, especially in low-light conditions where auditory cues may be less effective. Tactile communication is essential for bonding and conflict resolution, involving direct physical contact that conveys reassurance or intimidation. Mother-pup pairs frequently engage in nuzzling, where the female gently rubs her muzzle against the pup to reinforce attachment and guide nursing. In agonistic encounters, flipper-slapping or body shoving occurs between adults, serving as warnings or escalations in dominance hierarchies without escalating to full combat. These tactile interactions are instantaneous and precise, complementing vocal and visual signals in dense colonies. Certain earless seals exhibit acoustic adaptations that extend vocal communication beyond social signaling, such as frequency-modulated calls potentially aiding in prey detection akin to rudimentary echolocation. In leopard seals (Hydrurga leptonyx), underwater trills and hoots feature sweeping frequencies that may help locate prey under ice or in turbid waters, though this function remains under study. These calls, with source levels from 153 to 177 dB re 1 μPa at 1 m, demonstrate the versatility of phocid vocal repertoires across ecological contexts.

Social organization

Earless seals, members of the family Phocidae, display diverse social structures that generally emphasize solitude at sea contrasted with temporary aggregations on land or for key life stages such as breeding and molting. Most species, including harbor seals (Phoca vitulina), remain largely solitary during oceanic but form haul-outs comprising up to 1,000 individuals for resting and pup-rearing, fostering loose social bonds without rigid group cohesion. In contrast, northern elephant seals (Mirounga angustirostris) exhibit highly gregarious behavior, assembling in expansive rookeries of thousands during breeding seasons, where reflects defense and reproductive priorities. These land-based colonies highlight phocids' adaptive shift from individualism in marine environments to communal tolerance on substrates, minimizing energy expenditure while maximizing protection from predators. Dominance hierarchies among males are a of phocid , particularly in with polygynous , and are established through agonistic interactions involving vocalizations, displays, and physical confrontations. In elephant seals, marked males participate in a linear akin to a peck order, where alpha individuals secure control over large groups via repeated clashes that assess strength and resolve conflicts with minimal injury. Such hierarchies reduce overall by clarifying status, with subordinate males peripheralizing or awaiting opportunities to challenge superiors; vocal threats often precede , conserving in dense colonies. This structure ensures efficient resource allocation in crowded rookeries, though it varies by —less pronounced in smaller-group formers like harbor seals. Mother-pup relationships in phocids are characterized by intense, short-term bonding during , typically spanning 4 to 8 weeks, after which females abruptly wean and abandon pups to forage at sea, compelling independent development. This period involves constant proximity, vocal recognition, and nursing to rapidly build pup fat reserves, with separation risks minimized through mutual calling in noisy colonies. remains uncommon across most phocids but occurs notably in Hawaiian monk seals (Neomonachus schauinslandi), where females occasionally nurse unrelated pups, potentially aiding pup survival in sparse populations. Such dynamics underscore the capital breeding strategy of phocids, prioritizing maternal investment in a brief window before filial independence. Interspecific interactions among Antarctic phocids, such as Weddell (Leptonychotes weddellii), crabeater (Lobodon carcinophaga), and Ross seals (Ommatophoca rossii), often involve tolerance in shared haul-out zones, allowing coexistence amid overlapping distributions without frequent conflict. However, leopard seals (Hydrurga leptonyx) disrupt this through predatory behaviors, targeting pups of sympatric phocids like crabeater and Weddell seals to assert apex status. Kleptoparasitism by leopard seals, including prey theft from other pinnipeds in mixed assemblages, further illustrates opportunistic antagonism that influences community dynamics.

Reproduction and life history

Mating systems

Earless seals (family Phocidae) predominantly exhibit mating systems, in which dominant males mate with multiple females while most males do not reproduce. In species like the (Mirounga angustirostris), alpha males establish and defend harems of up to 50 females on breeding beaches, fasting for approximately three months to maintain territorial control and prevent other males from accessing the group. This extreme form of female-defense contrasts with milder variants in other phocids, such as harbor seals (Phoca vitulina), where males may mate with only two to five females using alternative tactics like aquatic displays rather than strict territorial defense. Overall, the degree of correlates with , with larger males gaining reproductive advantages through combat and displays. Courtship in earless seals involves a combination of vocal, visual, and physical behaviors to attract mates and establish dominance. Males often produce underwater vocalizations, such as the characteristic roars of harbor seals, to advertise during the breeding season, particularly in aquatically species. On land, rituals include neck-biting, flipper-waving, and aggressive posturing, as seen in elephant seals where males trumpet and charge to intimidate rivals. Copulation typically occurs either on land in terrestrial breeders like elephant seals or underwater in aquatic maters like harbor seals, lasting from seconds to a few minutes per event, with females often resisting initially before accepting. Breeding in earless seals follows annual cycles synchronized by photoperiod cues, leading to seasonal formations where females gather for concentrated pupping and . Northern hemisphere species, such as northern elephant seals, breed from to (winter to early spring), while southern species like the (Mirounga leonina) time reproduction to austral spring (September to November) for optimal foraging recovery post-breeding. These rookeries facilitate synchronized births, enhancing pup survival through herd protection. Many phocids feature delayed implantation, where the fertilized embryo remains unattached for 1 to 5 months—for example, 1.5 to 3.5 months in harbor seals and 3 to 4.5 months in southern elephant seals (northern elephant seals lack embryonic diapause)—allowing flexibility in gestation timing. Females employ strategies that maximize reproductive efficiency, including post-partum estrus in most species, enabling mating shortly after weaning pups and immediate re-impregnation via delayed implantation. favors larger, more vigorous males, as evidenced by higher copulation success among dominant individuals in polygynous harems, influencing genetic quality of offspring. This rapid reproductive turnaround supports annual breeding cycles despite the energetic costs of and migration.

Growth and development

Earless seal pups are born precocial, capable of swimming and limited shortly after birth. Many species, such as gray seals (Halichoerus grypus), are born with a coat—a fine, insulating that is shed within 2-4 weeks as the pup transitions to its adult pelage. Maternal is brief and energy-intensive, with mothers and drawing entirely from body reserves to produce milk high in fat (typically 40-60% lipid content), which supports rapid pup development. This nutrient-dense milk enables pups to triple their birth weight within the first month; for instance, (Pagophilus groenlandicus) pups gain approximately 2.2 kg per day during nursing, quadrupling their initial mass over 12-13 days. Weaning occurs abruptly after 4 days to 8 weeks, varying by —for example, 4 days in hooded seals, 12-13 days in harp seals, and around 16-21 days in gray seals—after which mothers depart to , leaving pups to fast and develop skills independently. During this post-weaning phase, pups lose 20-30% of their mass while learning to swim and hunt, facing high mortality rates of 10-30% in the first year due to , predation, and environmental challenges. Sexual maturity is attained between 3 and 8 years, with females generally maturing earlier (e.g., 4-5 years in harbor seals (Phoca vitulina)) than males (5-7 years). Full physical maturity, including maximum body size, is reached at 10-15 years, after which growth slows. Lifespans range from 15-40 years across species, with females often outliving males; in older individuals is marked by reduced reproductive output and diminished diving efficiency due to physiological decline. Growth and development are influenced by environmental factors, with rates generally faster in nutrient-rich polar waters where prey abundance supports higher intake compared to temperate or subpolar latitudes.

Ecology

Habitat and distribution

Earless seals (family Phocidae), consisting of 18 extant , are predominantly polar inhabitants, with 12 breeding on in the and regions, exemplified by the (Erignathus barbatus), which relies on seasonally ice-covered coastal waters and pack for essential stages. The remaining six breed on land, representing temperate and tropical outliers; for instance, the (Phoca vitulina) occupies nearshore coastal waters of the North Atlantic and North Pacific Oceans above approximately 30°N latitude. Tropical representatives include the (Monachus monachus), confined to the eastern Sea and adjacent Atlantic coasts, and the (Neomonachus schauinslandi), endemic to the , while the Caribbean monk seal (Neomonachus tropicalis) is extinct. These seals generally prefer continental shelf habitats, including ice floes and sub-ice leads for breeding and resting, as seen in the (Pusa hispida), which requires stable for forming snow-covered lairs over breathing holes and leads. Certain species, such as the northern and southern elephant seals (Mirounga angustirostris and Mirounga leonina), extend into deep oceanic waters up to 1,000 km offshore during extended migrations, though breeding occurs on coastal beaches and islands. Distribution patterns are often circumpolar within polar zones; the (Lobodon carcinophaga) exemplifies this with its continuous range encircling the continent in the pack ice zone of the . Vagrant individuals occasionally appear outside core ranges, including records of hooded seals (Cystophora cristata) in subtropical waters of the North Atlantic. Ongoing climate warming has induced range shifts in several populations, such as the northward expansion of harbor seals into formerly ice-limited Arctic areas since the 1980s, facilitated by sea ice retreat and warmer coastal conditions.

Diet and foraging

Earless seals, or phocids, display varied diets tailored to their environments, with most species relying heavily on fish and cephalopods as primary prey. Harbor seals (Phoca vitulina), for instance, feed primarily on a variety of fish such as herring, cod, and salmon, supplemented by cephalopods and crustaceans. In contrast, Antarctic specialists like the crabeater seal (Lobodon carcinophaga) consume over 95% krill (Euphausia superba), filtering up to 20 kg daily through specialized lobodontine teeth. The leopard seal (Hydrurga leptonyx) exhibits opportunistic feeding, incorporating krill, fish, squid, penguins, and occasionally young pinnipeds. Gray seals (Halichoerus grypus) favor benthic fish and squid, reflecting their nearshore preferences. Foraging strategies among earless seals emphasize solitary pursuits, with most dives lasting 5–20 minutes to target prey in benthic or pelagic zones. Gray seals often employ bottom-feeding in shallows, using suction to capture , while crabeater seals engage in pelagic filter-feeding within swarms at night. Pelagic chases are common in species like the leopard seal, which alternates between suction for small fish and grip-and-tear for larger prey. Group remains rare across phocids, prioritizing individual efficiency over cooperative hunts. Prey detection relies on sensitive vibrissae, which track hydrodynamic wakes from swimming targets, enabling precise localization even in low-visibility waters. Seals typically gulp or swallow prey whole, minimizing handling time; for example, suction-feeding dominates in harbor and gray seals for quick benthic ingestion. Seasonal dietary shifts occur, with increased cephalopod intake—such as squid—during winter months for species like gray seals, aligning with fish migrations. These adaptations, including specialized dentition for piercing or filtering, facilitate efficient capture across feeding modes. Foraging phocids support metabolic demands through high-calorie prey like fatty . During breeding seasons, many fast for weeks, relying on reserves accumulated from prior bouts to offset energy deficits. This balance ensures survival amid variable prey availability, with post-breeding trips replenishing stores rapidly.

Conservation status

The conservation status of earless seals (family Phocidae) varies across species, with most classified as Least Concern by the IUCN Red List, though several face elevated risks due to ongoing threats. The Hawaiian monk seal (Neomonachus schauinslandi) is Vulnerable (as of 2025), with a population of approximately 1,580 individuals (as of 2024) primarily in the Northwestern Hawaiian Islands. The Mediterranean monk seal (Monachus monachus) was downlisted to Vulnerable in 2023 following population increases, now estimated at fewer than 1,000 individuals concentrated in Greece, Turkey, and Cyprus. Other threatened species include the hooded seal (Cystophora cristata), uplisted to Endangered in 2025 due to reproductive declines, and the Caspian seal (Pusa caspica), also Endangered with ongoing population reductions. The southern elephant seal (Mirounga leonina) is currently Least Concern but shows concerning declines at key sites, potentially prompting reassessment amid disease outbreaks like avian influenza. Species such as the Baikal seal (Pusa sibirica) are Least Concern but data-deficient in some regions, highlighting gaps in monitoring. In October 2025, the IUCN updated statuses for several phocids, uplisting Arctic ice-dependent species like the ringed, bearded, and harp seals to Near Threatened due to climate impacts, while downlisting the Hawaiian monk seal to Vulnerable. Major threats include historical overhunting, which drastically reduced populations; for instance, northern elephant seals (Mirounga angustirostris) were hunted to near extinction, with only about 20-100 individuals surviving by the 1890s. Contemporary pressures encompass climate change, which exacerbates sea ice loss critical for Arctic species like ringed, bearded, and harp seals, contributing to their uplistings to Near Threatened in 2025 and affecting whelping and foraging habitats. Bycatch in fisheries remains significant, with estimates of around 555 harbor seals (Phoca vitulina) drowned annually in Norwegian gillnets alone, and broader North Atlantic incidents exceeding 2,000 for related phocids. Emerging issues involve pollution, such as PCB bioaccumulation in Baikal seals leading to reproductive impairments, and tourism disturbances at rookeries that disrupt haul-outs and pupping for species like monk seals. Conservation efforts have yielded notable successes through protective measures and international agreements. Hunting bans, including the U.S. Marine Mammal Protection Act of 1972 and Canadian restrictions on harp seal pup harvests in the 1970s, facilitated recoveries such as the northern elephant seal population, which rebounded to over 225,000 individuals. The Convention for the Conservation of Antarctic Seals (1972), under the Antarctic Treaty System, prohibits commercial harvesting south of 60°S and establishes quotas for krill-dependent species like the southern elephant and Weddell seals, supporting stable populations. Marine protected areas, such as those in the Hawaiian Islands and Mediterranean, combined with rehabilitation and anti-bycatch gear initiatives, have boosted Hawaiian monk seal survival by an estimated 30%. Ongoing monitoring and reduced non-climate threats are essential to counter climate-driven declines in ice-associated species.

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