True seals

(Phocidae)

Class Mammalia

Order Carnivora

Suborder Pinnipedia

Family Phocidae

Thumbnail description
Large marine mammals that are fusiform in shape; crawls on its stomach on land or ice using either a caterpillar movement (on land) or swishing its rear end from side to side (on ice); propels itself in water by thrusting rear flippers from side to side, fanning the leading flipper and closing the trailing one; foreflippers are short and not used as rudders much in aquatic or terrestrial movement, other than to push off the ground on land; coloration varies from solid color to mottling or spotted with dark on light background or the reverse

Size
Approximately 3–15 ft (1–5 m); approximately 100–5,700 lb (45–2,600 kg)

Number of genera, species
13 genera; 19 species

Habitat
Shallow and deep marine areas, polynyas (open water within large ice masses), drifting ice floes, and island and mainland beaches (sand, cobble and rock)

Conservation status
Extinct: 1 species; Critically Endangered: 1 species; Endangered: 1 species; Vulnerable: 1 species; Near Threatened: 1 species; Data Deficient: 1 species

Distribution
Circumpolar and occupying temperate latitude waters in the Northern and Southern Hemisphere; subtropical for one species in the Pacific Ocean

Evolution and systematics

The family Phocidae is the oldest of the modern day pinnipeds, with the oldest fossil phocid reported from the late Oligocene or about 25–30 million years ago. The current phocids originated in the North Atlantic and consists of two subfamilies, the Monachinae and the Phocinae. The Phocinae contains five genera and the Monchinae six genera. The phocids along with the other two families of current pinnipeds, the otariids (fur seals and sea lions) and odobenids (walrus), appear to have evolved from a single lineage of either a bear-like, otter-like, or raccoon-like ancestor. Most evidence points toward bear or otter-like ancestry but there is conflicting evidence.

Physical characteristics

Phocid seals range from moderate to large size. Most are fusiform in shape, but the leopard seal is almost tubular looking, being longer and more slender. All phocids are characterized by having relatively short hair that lies smooth along the body, thick skin and a thick subcutaneous layer of blubber that can be 5–6 in (11–13 cm) thick to insulate the animal and provide energy stores when not foraging. The foreflippers are small while the rear flippers are large and contain webbing between the digits that expands them into paddles, which provide thrust for swimming. All phocids appear to have no neck; the head blends into the trunk of the body. They have no external pinnae (ear), minimizing structures that would produce drag during swimming. Males of some species such as elephant seals (Mirounga spp.), hooded seals (Cystophora cristata), and gray seals (Halichoerus grypus) have enhanced (elongated or inflatable) snouts that are used in competitive social contexts.

Distribution

The majority (14 species) of phocids are found in the Northern Hemisphere although five species occur south of

the equator. In both hemispheres many species are circumpolar or subpolar, there are a few temperate species, such as gray seals, elephant seals, and harbor seals (Phoca vitulina). Three species of monk seals (one of which has gone extinct in the past century) inhabit subtropical or tropical regions of the Pacific, Mediterranean and Caribbean waters. Virtually all major oceans, except the Indian Ocean, contain phocid species. There are even two species found in large inland lakes, the Baikal seal (Phoca sibirica) of Lake Baikal in Siberia and two subspecies of ring seal (Phoca hispida) found in Lake Ladoga and Lake Saimaa of Russia and Finland, respectively. There may also be a subspecies of harbor seal that inhabits inland lakes in the Ungava Peninsula of Quebec, although it is unclear if these animals are completely isolated.

Habitat

All species forage at sea but use either land or ice to produce their pups, to molt, and to rest. Mating occurs on land in a few species and in the water in most; occasional mating on ice has been seen but usually seals that give birth on ice mate in the water.

Land habitats used are variable, including sand, cobble and boulder beaches, rocky outcroppings, and caves (gray seals and Mediterranean monk seals [Monachus monachus]). Some species like gray and harbor seals may use all or most of these different land habitats as well as ice in some locations.

Ice habitats used by phocids include both floe ice and land fast ice. The former is free floating and the size of ice pans is highly variable. The latter consists of large ice masses affixed to land masses and are usually more stable.

Behavior

Most phocid species are gregarious during an annual molting period, when they haul out on land or ice to shed their hair and acquire a new coat. Many species form colonies during an annual breeding period, with species like elephant seals forming large dense harems of over a hundred females and a few males, all lying in contact with one another, to dispersed male-female pairs of hooded or crab-eater seals (Lobodon carcinophagus) a half mile (0.8 km) or more apart on floating ice pans.

Males and females of many species migrate from breeding areas to separate areas used for foraging. In some cases these migrations are associated with seasonal changes in ice patterns. Other species remain in the vicinity of the seasonal breeding areas for feeding or disperse in a more random pattern rather than migrating.

Researchers are only beginning to learn more details about foraging tactics as a result of a few studies that have attached cameras to free-living seals to record the behavior of the seals during foraging. One such study of harbor seals shows that some males use a tactic of digging in the bottom substrate for species that bury themselves in sand while others find and follow schools of fish, picking off individual fish that leave the school and go to the bottom to avoid the seal.

Feeding ecology and diet

There is a strong link between the breeding pattern, body size, and feeding ecology in phocid seals. The relatively large size of phocids allows them to build body stores of fat that fuel breeding without foraging for periods of time (a phenomenon known as capital breeding). Some of the smaller phocids, however, such as the harbor seal, may have to forage some during the breeding period to rear their young successfully because they cannot store enough fat. The ability to store fat and fast during breeding means that foraging grounds can be separated by considerable distances from breeding grounds in these species. Northern elephant seals (Mirounga angustirostris), for example, are known to leave breeding and resting areas to travel about 12,000 mi (20,000 km) during two major foraging periods, after breeding and after molting.

The diets of phocid seals may be varied both within and among species, including varying seasonally as food resources change or as the location of seals change seasonally. Crabeater seals, for example, eat krill (small shrimp-like organisms) almost exclusively, whereas leopard seals eat penguins, other seals, fish, krill, squid, octopus, and other invertebrates. Fish of one sort or another is the primary diet of most phocid species.

To obtain the energy-rich food and dense patches of fish, phocids often have to dive to considerable depths. Elephant seals will dive to depths as deep as about 5,000 ft (1,500 m), staying underwater from 20 to 60 minutes while they forage for squid. Other species, like harbor seals in some locations, regularly forage only at depths of 80–200 ft (25–60 m), whereas at other locations may forage more often at about 650–825 ft (200–250 m). The shallower dives are usually much shorter in duration, lasting more in the range of three to five minutes.

Reproductive biology

All phocids have an annual reproductive cycle in which females give birth during a fairly distinct breeding period. They are particularly noted for short lactation periods, lasting from as little as four days in the hooded seal to as long as two to three months in a couple of species. Females become receptive near the end of lactation or shortly thereafter in all species. Females of all species exhibit delayed implantation or embryonic diapause during which the fertilized ovum suspends development and remains in the uterus without implanting. This is thought to help synchronize parturition among females and produce the highly synchronous breeding seasons found in these species.

The short lactation periods of phocids are associated with fasting or feeding little during this time. Also associated with this is the buildup of extensive blubber layers by females to provide the major nutrients to produce milk for the young. Milk fat content is highest in those species with the shortest lactations, as is pup mass gain. Females may lose over 40% of their mass at the beginning of the breeding season and between 60% and 80% of that loss is in the milk transferred to the pup. Males do not participate in the care of offspring in any species.

Males of all phocids fast or feed little during the period when receptive females are available. Consequently, they too build up extensive blubber layers prior to the mating season

to fuel the energy-intense competition for access females. Mass loss as a percentage of initial body mass in males, however, is not as great as it is in females. Among several species for which there are such data, the average percentage loss is between 15% and 35% compared to the values given above for females.

Mating patterns in phocids is best known among the three species that mate on land: gray seals and the northern and southern elephant seals. In these cases, the primary mating tactic is one of defending females directly. Recent studies, which use genetic paternity analyses, show that there may be alternative tactics that are more opportunistic but are also

successful, even if to a lesser degree. For example, gray seal males that defend and mate with females before they depart only fertilize about 22% of them and males that capture and mate with departing females, fertilize about 9% of the females they capture. A few studies of a couple of species that mate at sea suggest that males may be more likely to engage in efforts to attract females by displaying than guarding them directly; such a mating system is known as a lek-type system. Females may actually choose their mates in this system, although the evidence for female choice is not strong for any of these species yet.

Females begin producing a single young each year from four to seven years of age, whereas males become sexually mature a couple of years later than females in many species. Furthermore, males do not become socially competitive for several additional years; they may be 10 years old or more before they succeed in mating. Research seems to indicate that both males and females are potentially reproductively active until they die. There is some evidence in a few species to suggest older females may not perform as well as middle-aged females in rearing fat, healthy pups. The youngest and inexperienced mothers may also perform poorly.

Conservation status

The main factor leading to extinction, endangered, or threatened status of phocids has been hunting pressures from humans within the past century or two. More recently, the Hawaiian monk seal (Monachus schauinslandi), which was showing signs of coming back in the mid-1900s, was probably disturbed by military operations on the small islands used for breeding and molting, and produced poor recruitment into the breeding population. Subsequently, signs of environmental regime shifts that have caused a change in carrying capacity may be inhibiting the return of this species. It is currently listed as Endangered. Likewise the Mediterranean monk seal is Critically Endangered, and continuing to decline to near extinction (fewer than 500 seals remaining) despite protection, because of degradation in its environment. Recent disease problems producing mass die-offs can probably be attributed to the poor state of the environment. One species has gone extinct in the past 100 years, the West Indian monk seal (Monachus tropicalis). It is the cousin to the other two monk seals. The cause of this extinction was likely hunting pressure. Additionally, the Caspian seal is listed as Vulnerable, and the Baikal seal is listed as Lower Risk/Near Threatened by the IUCN.

Significance to humans

True seals have been hunted for hundreds of years, serving as a source of food, oil, and hides or furs. In recent years, these products have been boycotted as a result of public pressure

against clubbing pups, and the market for these items has nearly vanished. Subsistence hunting of some species occurs on a very small scale. Commercial hunting of at least two species, harp and hooded seals, continues annually, but at a very reduced level. These hunts take many fewer pups than in the past and have a small market for the products. One offshoot of the pressure against hunting has been the evolution

of a small eco-tourism industry centered on trips to the pack ice during the harp seal breeding season. As these trips are expensive, the industry is likely to remain small for species such as harp seals. However, for species like the northern elephant seal, which now breeds in accessible mainland colonies, controlled nature programs have become successful educational experiences.

Species accounts

List of Species

Gray seal

Halichoerus grypus

subfamily

Phocinae

taxonomy

Halichoerus grypus (Fabricius, 1791), "Greenland."

other common names

English: Horsehead seal, Atlantic seal, Atlantic gray seal, Baltic gray seal.

physical characteristics

Males: 7.1 ft (2.3 m); 595 lb (271 kg); Females: 6.2 ft (2 m); 455 lb (207 kg). Males are noted for their large curved snout, which females do not have. Males generally have a dark pelage (black or charcoal gray) that is sometimes mottled with gray patterns; females generally have lighter gray pelage that is usually mottled with black patterns. Both show considerable variation. Pups are born with white lanugo.

distribution

Eastern and western North Atlantic Ocean, Baltic Sea.

habitat

Breed on island beaches (sand, cobble, boulders) and on ice floes. Forage in waters ranging from 124 to 775 ft (40–250 m) deep.

behavior

Breed in colonies of varying densities. Ice-breeding colonies are usually less dense. Individuals tend to return to the same breeding colony every year. Large molting groups form on islands during the spring and early summer.

feeding ecology and diet

Considerable individual variation in foraging strategy, ranging from migrating to a foraging ground, randomly searching and coming and going from a fixed resting place to a particular foraging patch. Primarily eat fish; the principal species eaten varies by location, but includes cod (Gadus morhua), capelin (Mallotus villosus), and sand eels (Ammodytes spp.).

reproductive biology

Males are polygynous with the most successful males defending clusters of females, but other successful tactics involve mating opportunistically with departing females that have already mated. Males do not succeed in mating until age 12–15 years. Females produce a single pup annually beginning at about age four to six years. Lactation lasts about 17 days and pups are fed milk that is about 60% fat.

conservation status

Not threatened. Populations are protected and growing at substantial rates of greater than 12% annually. In 2002, the largest breeding colony, Sable Island, Nova Scotia, produced 50,000 pups.

significance to humans

At one time they were hunted for their pelts and blubber (rendered into oil). They are no longer hunted and in some instances have become a nuisance to aquaculture and certain fisheries.

Harbor seal

Phoca vitulina

subfamily

Phocinae

taxonomy

Phoca vitulina Linnaeus, 1758, "in mari Europaeligo."

other common names

English: Common seal, kuril seal, island seal, spotted seal.

physical characteristics

Males: 5.3–6.3 ft (1.6–1.9 m); 194–312 lb (88–142 kg); Females: 4.9–5.6 ft (1.5–1.7 m); 143–235 lb (65–107 kg). There is considerable variation in pelage coloration both within and among the five subspecies of this species; there is no difference between the sexes. The Atlantic subspecies have background color of various shades of gray or cream covered with dark spots. The Pacific subspecies have light and dark variants of coat color. The dark pelage consists of dense black spots, some of which are outlined by a silver ring. The light pelage has a darker upper body but the sides and underbody have a silvery background with dark spots. Most pups are born without a white natal coat, which has been shed in utero. Consequently, they look like miniature adults.

distribution

These seals are found broadly in the Northern Hemisphere in coastal areas of both the east and west Atlantic Ocean and of the east and west Pacific Ocean.

habitat

Breed, rest and molt on sand and cobble beaches, rocky islets, sand bars and occasionally ice floes. They may forage in estuaries, along the continental shelf or in deeper waters off the shelf. One population is found in an inland lake.

behavior

During the breeding season, males and females with pups form small mixed groups on land in areas traditionally used for pupping. There is no clear organizational structure to these groups. Males spend less time on land at this time than do females with pups. Several weeks after breeding, both sexes haul out to molt. Molting groups may be much larger than the size of groups during breeding. During intensive foraging between breeding and molting, seals disperse to forage rather than migrate to specific forage areas. Harbor seals engage in little inair vocalizations, but during the mating period males appear to use underwater displays that have visual and vocal components. Females of this species make foraging trips during lactation, similar to those seen in otariid seals.

feeding ecology and diet

Foraging patterns and diets of this species are highly variable and depend on local environments. Around Sable Island in Atlantic Canada, foraging is typically at depths of 66–165 ft (20–50 m), whereas in areas of the Pacific it is not uncommon for foraging depths to exceed 330 ft (150 m). The primary food for this species is small to medium size fishes followed by cephalopods (such as squid and octopus). While there may be many species identified as prey items for a given population,

there is usually a couple of species that predominate and this may vary seasonally and inter-annually. At Sable Island, sand eels (Ammodytes spp.) predominate. Around the Aleutian Islands in the Pacific, Atka mackerel (Pleurogrammus monopterygius) is the main fish eaten. On another level, diets in the Moray Firth of Scotland showed Atlantic cod (Gadus morhua) as the main food in January, whereas in June cod was the dominant prey. In January two years later herring (Clupea harengus) was the major food.

reproductive biology

Mating in this species occurs at sea so it has been difficult to study the mating system. Recent studies using dive recorders, video cameras, hydrophones, and DNA analyses have begun to reveal some information. Males appear to be polygynous, but at a fairly low level (maximum success of fertilizing five females). In some locations, males may defend territories to control access to females and in others males may display (blowing bubbles and vocalizing) from aquatic positions to attract females. Much more research is needed to confirm such patterns. Males produce sperm about three to seven years of age but do not become successful breeders until older, probably at least 10 years of age. Females give birth for the first time from three to seven years of age, and give birth to a single young annually. Lactation is about 24 days and females produce milk averaging 50% fat. As noted above, females do not fast entirely during lactation and begin regular foraging trips to supplement blubber stores to fuel the production of milk during lactation.

conservation status

This species is not threatened, but several major die-offs have occurred in recent years with thousands of seals dying from diseases not previously known to be a problem. The coastal nature of this species makes them particularly vulnerable to human-induced impacts such as pollution.

significance to humans

There are small amounts of subsistence hunting of these seals for food and hides, but the species is of no major significance to humans.

Harp seal

Pagophilus groenlandicus

subfamily

Phocinae

taxonomy

Pagophilus groenlandicus (Erxleben, 1777), "in Groenlandiaet Newfoundland."

other common names

English: Fjord seal, jar seal; Eskimo: Natchik.

physical characteristics

Males: 5.6 ft (1.7 m); 297 lb (135 kg); Females: 5.6 ft (1.7 m); 240 lb (109 kg). Young adults of both sexes have a silvery gray coat with dark spots. Older adult males have basic pelage that is cream color over which is a black face to the top of the head and a matching harp or saddle pattern of black running along each side. Older females have a similar pattern but the harp pattern and face may not be as dark and sometimes it is broken into smaller patterns. Pups are born with a white natal coat.

distribution

There are three major breeding areas, one off the coast of northeastern Canada, another off the east coast of Greenland, and the third in the White Sea off the northwest coast of Russia. Outside of the breeding season seals may be found mainly in subarctic areas of the North Atlantic Ocean.

habitat

Breed on ice floes and remain in association with pack ice for resting and molting. They forage in open water or under the ice. Their ice-breeding habit makes this species particularly prone to polar bear predation during breeding.

behavior

Females form large aggregations on floating ice during the breeding season but are not densely clumped like in some species. Males spend little time on the ice during this time. After the breeding period, both sexes haul out in groups on the ice to molt. After molting, seals migrate northward with the recession of the ice to areas where they forage intensively, having foraged little during breeding and molting. In-air vocalizations are relatively uncommon although females will give shrill calls when another animal approaches their pup too closely. Underwater around the breeding grounds there is a cacophony of sounds, most likely emanating from males although it is difficult to identify who is doing the vocalizing. Weaned pups remain on the ice and fast for several weeks before they depart to begin foraging.

feeding ecology and diet

Diets of this species have been extensively studied from stomach samples of shot seals, but only recently have dive recorders been used to determine at what depth seals feed. Moreover these data are only available during the breeding season, which may be expected to be different than at other times. During this period, seals are moderate divers potentially foraging at depths averaging 100 ft (30 m) and reaching a maximum of 300 ft (90 m). These dives typically last about four minutes, but may last as long as 13 minutes. The diet is broad and known to vary seasonally. Nearly 70 species of fish and 70 species of invertebrates have been found in the stomachs of these seals. The most predominant species are capelin (Mallosus villosus), and Arctic (Boreogadus saida), and polar cod (Arctogadus glacialis).

reproductive biology

The mating system is poorly studied in this species. Males are believed to be polygynous, but whether they defend positions, territories, or females directly, or display to attract females is unclear. Mating occurs in the water. Males produce sperm about four to five years of age, although may not become successful breeders until older. Females give birth for the first time from four to seven years of age, and give birth to a single young annually. Lactation is about 12 days during which females produce a milk averaging 48% fat.

conservation status

Not threatened.

significance to humans

These seals are hunted for meat, fur, and oil on a small scale. Also a small eco-tourism industry has evolved out of the efforts to replace the lost economy from boycotts of seal products resulting from hunting.

Baikal seal

Phoca sibirica

subfamily

Phocinae

taxonomy

Phoca sibirica Gmelin, 1788, Lake Baikal.

other common names

None known.

physical characteristics

Length 3.4–4.3 ft (1.1–1.4 m); weight 100–285 lb (45–130 kg); pelage is silver gray on back and yellowish white on the belly. Pups are born with a white natal coat.

distribution

Lake Baikal, Siberia.

habitat

This species is unusual in that it is one of two known to inhabit freshwater (or brackish water) exclusively. It uses ice lairs or dens in the fast ice to breed and haul out on to molt in the spring. Baikal seals haul out on lake shore or rocky outcroppings to rest in the summer.

behavior

Seals are dispersed during breeding, occupying birth lairs that occur where ice hummocks form. Resting and molting groups form after breeding. These groups may contain several hundred seals.

feeding ecology and diet

There are no other mammalian carnivores with which this seal competes for food and are capable of eating most fish species available except perhaps a large sturgeon (Acipenser baeri). The four main fish species in the diet are the greater golomyanka (Comephorus baicalensis), the lesser golmyanka (C. dybowskii), the Baikal yellow fin sculpin (Cottocomephorus grewingki), and the longfin sculpin (C. comephoroides). The diets are more variable in the summer than in the fall.

reproductive biology

Males are thought to be polygynous but little detailed information is available because mating occurs underwater or in breeding lairs. Male wounds are uncommon compared to other species where males compete aggressively for females. Males produce sperm by seven years of age but by what age they are socially active is not known. Females begin to produce pups at five to six years of age and continue until about 30 years of age. They give birth to a single young annually. Lactation is imprecisely known, being reported to last from between 1.5 to 2.5 months.

conservation status

Listed as Lower Risk/Near Threatened by the IUCN.

significance to humans

Hunted for subsistence but of no major significance.

Weddell seal

Leptonychotes weddellii

subfamily

Monachinae

taxonomy

Leptonychotes weddellii (Lesson, 1826), South Orkney Island.

other common names

None known.

physical characteristics

Males: 8.0 ft (2.4 m); 748 lb (340 kg); Females: 8.3 ft (2.5 m); 836 lb (380 kg). Pelage of both sexes is usually black with grayish silver streaks. Pups are born with a grayish natal coat that has a darker stripe on top of the back.

distribution

Circumpolar around Antarctica.

habitat

Inhabits fast ice exclusively although individual animals may occasionally be seen on island beaches.

behavior

Breed in colonies where both males and females spend time on the ice and in the water, although younger males are usually not tolerated on the ice with females. Females take their pups into the water within two weeks of birth. Males fight under water and give loud trilling vocalizations that may be advertisements to females or other males. There is not a routine migration from breeding sites. Seasonal movement usually follows the expansion and recession of the ice.

feeding ecology and diet

Data from dive recorders show that seals dive to depths of 1,150–1,480 ft (350–450 m) in the spring and early summer but to shallower depths 164–660 ft (50–200 m) in late summer, suggesting possible seasonal changes in diets. Their diet is broad, consisting of fish, cephalopods (squid and octopus), krill (Euphausa superba), and other invertebrates. Consistent with seasonal changes in dive profiles, one study found bottom and near bottom species in spring stomach samples collected and mid-water species in later summer.

reproductive biology

Males are polygynous and defend positions in the water where there are traditional openings in the ice every year. These positions may be exclusive territories, but data are not sufficient to be conclusive. Mating occurs in the water. Males produce sperm about three to six years but do not become successful breeders until older. Females give birth for the first time from three to seven years of age. They give birth to a single pup annually. Lactation is about 58 days and females produce a milk averaging 48% fat.

conservation status

Not threatened, but are protected by the international Antarctic Treaty.

significance to humans

These seals are of not particular value to humans.

Northern elephant seal

Mirounga angustirostris

subfamily

Monachinae

taxonomy

Mirounga angustirostris (Gill, 1866), California.

other common names

English: Northern sea elephant.

physical characteristics

Males: 13.2 ft (4.0 m); 3,750 lb (1,704 kg); Females: 10.6 ft (3.2 m); 1,122 lb (510 kg). Males differ from females in that they have an enlarged proboscis and more highly developed neck with thickened skin than females. The pelage of males is dark gray upper and lighter gray under; females are browner than males and darker. Pups are born with a near black natal coat.

distribution

The breeding range is from northern California to the Baja Peninsula in Mexico. During foraging periods, seals migrate north as far as the Gulf of Alaska and the Aleutian Islands.

habitat

Breed and molt on mainland and island beaches of sand and cobble. Forage in deep ocean waters.

behavior

Breed in dense colonies where both males and females show strong site fidelity from one season to the next. Males make a distinct vocalization during breeding using the proboscis as a resonating chamber. These calls have dialects for different locations. Animals migrate after breeding to foraging areas and return to the breeding location to molt. After the molt, animals again migrate, making a double roundtrip of over 6,000 miles (10,000 km) each.

feeding ecology and diet

Males and females forage in different locations and in different ways. Male go further away from breeding grounds and forage at shallower depths on average than females, and males forage on the edge of the continental shelf, whereas females forage more in open ocean. By two years of age, young seals show similar patterns to adults. Feed mostly on cephalopods (such as squid and octopus) and Pacific whiting fish. The diving pattern of these seals is remarkable. They dive continuously for weeks remaining underwater for 30–120 minutes and going to depths as deep as about 5,000 ft (1,500 m), averaging about 1,650 ft (500 m) for females and 1,090 ft (330 m) for males.

reproductive biology

Males are polygynous and in most areas defend harems or large groups of densely packed females. Mating occurs on land and females often mate with males other than the harem master as they leave for sea. Males produce sperm about five years of age but do not become successful breeders until 10 to 12 years. Successful males may only breed for two to four years before they are displaced. Females give birth for the first time from three to seven years of age. They give birth to a single young annually. Lactation is about 27 days and females produce a milk averaging 54% fat.

conservation status

Not threatened.

significance to humans

These seals are of no particular value to humans other than as an educational experience. Their approachability and close proximity to urban areas allow for controlled visits to learn about their biology and natural history.

Hawaiian monk seal

Monachus schauinslandi

subfamily

Monachinae

taxonomy

Monachus schauinslandi Matschie, 1905, Laysan Island, United States.

other common names

Spanish: Foca fraile de Hawaii.

physical characteristics

Males: 6.9 ft (2.1 m); 385 lb (175 kg); Females: 7.5 ft (2.3 m); 528 lb (270 kg). Males and females are similarly colored slate gray on the upper part of their body and a light silvery gray below. Pups are born with a black natal coat.

distribution

This species occurs only in the Hawaiian Archipelago. Its current distribution is mainly at a chain of small, remote islands known as the northwestern Hawaiian Islands, although it has recently begun to re-inhabit the main Hawaiian Islands in small numbers. In the past, they may have occupied islands outside the Hawaiian Archipelago such as Johnston Atoll, Wake Island, and Palmyra Atoll.

habitat

The small islands and atolls used by monk seals for breeding, molting and resting are made up of coral sand. The parts of islands used for breeding usually have a shallow coral shelf where females and pups can cool off during the peak heat of the day and be afforded protection from large sharks that prey upon the pups. Foraging habitat appears to be primarily among the coral reef habitat although some areas of open ocean off the shelf may also be used.

behavior

During the breeding season females haul out on islands, remaining close to the water and tend to be evenly dispersed rather than clustered. Males spend little time hauled out on these beaches with females, but periodically visit them to check their reproductive status. During molting, males and females tend to be more aggregated on land than during breeding. Seals do not migrate from their breeding or molting beaches to forage. They forage in or near the atolls or islands where they rest, molt, and breed. The subtropical latitude inhabited by monk seals requires spending time in the water daily to keep cool. As a result, few animals are hauled out during the middle part of the day when temperatures and solar radiation are at their highest levels.

feeding ecology and diet

The monk seal diet is varied and differs among the islands and the different age groups of seals. Over 40 species have been recorded from scats. The most common type of food is marine eels (Congridae, Muraenidae, and Ophicthidae), and various reef fishes such as wrass (Labridae), squirrelfish and soldierfish (Holocentridae), and triggerfish (Balistidae). Much smaller amounts of squid, octopus and lobster were also found. Recent studies using a video camera attached to a small number of free-ranging seals showed most foraging to occur at or near the bottom, and provided images of seals turning over rocks and debris on the bottom. From these camera studies and studies using dive recorders, the depths at which foraging occurs is highly variable. For some individuals it may be well under 330 ft (100 m) and for others it may be in excess of 495–990 ft (150–300 m). This is an area of study needing further effort.

reproductive biology

Males are believed to be polygynous, however, mating is seen infrequently because it occurs in the water. Some evidence suggests that individual males may follow individual receptive females at sea for a period of time until mating with them, a tactic known as roving or scramble competition. More studies are necessary to gain a better understanding of mating tactics and success. The age at which males produce sperm is not well known. Females give birth for the first time from about five to six years of age. They give birth to a single young annually. Lactation is about 44 days but the milk's fat content is not known in this species. A highly unusual pattern of switching of pups occurs frequently in this species. As many as 87% of the females in a colony will switch pups during the breeding season at least once following fights between females. The reasons for this behavior are unclear, although higher-density colonies have higher rates of switching. The behavior does not appear to effect pup survival. The breeding season of monk seals is much more extended than in most other phocids, lasting six months or more.

conservation status

This species is Endangered. For the past decade, the population has hovered around 1,500 seals. It is likely to decline dramatically over the next decade because of a lack of young cohorts being recruited into the breeding population. As older breeding animals die there will be few new ones at many of the colonies. Past declines may have been related to human disturbance by military installations on some of the islands, but those have been controlled or removed for some years, yet the population fails to expand. Major environmental changes, called regime shifts, may have affected the capacity of the environment to provide adequate food for this species. There may also be indirect effects from humans, too; entanglement in discard nets are known to kill monk seals and poor fisheries management (e.g., lobsters) may have helped to diminish monk seal food resources.

significance to humans

In recent times monk seals have been of no significance to humans. A current problem is arising with the increased use of the main Hawaiian Islands by monk seals. They are hauling out on major tourist beaches, and their protective status as an endangered species has resulted in the closure or restriction of the use of these beaches. Managing such situations presents a challenge so as to not turn the public against this fragile species, which could easily become extinct before the end of this century.

Hooded seal

Cystophora cristata

subfamily

Monachinae

taxonomy

Cystophora cristata (Erxleben, 1777), south Greenland and Newfoundland.

other common names

English: Bladdernose seal.

physical characteristics

Males: 8.3 ft (2.5 m); 660 lb (300 kg); Females: 7.3 ft (2.2 m); 440 lb (200 kg). Males and females have similar pelage that is a gray background with black patches. Pups are born with a coat that is blue-gray above and creamy color below. It is not the natal coat as found in most other phocids. The real natal coat in this species is shed in utero. The name hooded seal is derived from the enlarged naval cavity of adult males that can be inflated into a hood. The nasal septum membrane of males can also be inflated and extruded into a balloon-like structure. Females do not have these structures and the structures are not adequately developed in young males to be inflated.

distribution

There are four major breeding areas: two on ice off northeastern Canada (the Gulf of St. Lawrence and off Newfoundland/Labrador) and two on ice around Greenland (off the west coast and off the east coast). Molting occurs primarily on ice off the east coast of Greenland and near Iceland in the Denmark Strait. Foraging areas range from Labrador, around Greenland and Iceland to Spitsbergen.

habitat

Breed on ice floes and remain in association with pack ice for resting and molting. They forage in open water along the ice edge. Their ice-breeding habit makes them particularly prone to polar bear predation during breeding.

behavior

Females are highly dispersed on floating ice during the breeding season, although occasionally two or three females may be within 100 ft (30 m) of one another. Males spend brief periods of time on the ice during this time. After the breeding period, both sexes migrate, probably feeding as they travel, to traditional areas where they haul out in groups on the ice to molt. Following molting, seals disperse to feed, moving with the recession of the ice to forage along the ice edge. Weaned pups remain on the ice fasting for several weeks before they depart to begin foraging.

feeding ecology and diet

Little information on diet is available but these seals are known to forage on fish and squid in deep water. They typically dive to depths of 330–1,980 ft (100–600 m), remaining underwater for more than 50 minutes. They have been known to forage at depths of over a 3,300 ft (1,000 m) and remain underwater for over an hour. Among the fish species in their diet are redfish (Sebastes spp.), (capelin Mallotus villosus), herring (Clupea harengus), Arctic cod (Boreogadus saida), and Atlantic cod (Gadus morhua).

reproductive biology

Males are polygynous, with successful individuals moving from female to female and fighting with other males to maintain access to a female until she is mated. Through this sequential defense of females, an individual male may succeed in mating with as many as eight or more females during the short two-week mating period. This competition among males and mating occurs mostly in the water. Males produce sperm about four to six years of age, but do not become successful breeders until older. Females give birth for the first time from four to nine years of age. They give birth to a single young annually and have the shortest lactation known for any mammal. Pups are nursed for only four days before being weaned abruptly. Females produce a milk averaging 61% fat, allowing pups to gain 15.5 lbs (7 kg) per day and more than double their mass before being weaned.

conservation status

Not threatened.

significance to humans

These seals are hunted for meat, fur, and oil on a small scale.

Crab-eater seal

Lobodon carcinophagus

subfamily

Monachinae

taxonomy

Phoca carcinophaga (Hombron and Jaquinot, 1842), Scotia Sea (midway between South Orkney and South Sandwich Islands).

other common names

English: White seal.

physical characteristics

Males and females are similar in size: 7.6 ft (2.3 m); 490 lb (223 kg). Adult pelage is silvery with patches of brown on the upper body and leading edges of the foreflipper. The pelage fades to a creamy white before the next molt. Pups are born with a light brown natal coat. Body shape is less fusiform and more tubular.

distribution

Circumpolar among the floe ice in the Southern Hemisphere.

habitat

Remain among the pack ice for breeding, molting, and foraging.

behavior

Females with pups and males are dispersed as trios during the breeding period. Large groups of seals are not seen even during the molting period in January, although the numbers of seals seen in an area increases during this period. Little is known about the behavior of this species because of their dispersed distribution in the pack ice. They are migratory by virtue of moving with the seasonal changes in the distribution of the ice.

feeding ecology and diet

These seals are specialized in their diet, feeding almost exclusively on Antarctic krill Euphausa superba, and do not change their diet seasonally. About 5% of their diet consists of fish and squid species. Most foraging is done at night, when the vertically migrating krill are at shallower depths. Only a few seals have been outfitted with dive recorders and these animals typically dived to less than 165 ft (50 m) with a maximum depth of about 2,750 ft (530 m).

reproductive biology

Males may be polygynous but studies following known individuals have not been done, nor have DNA analyses examined paternities. Males do guard females, following the females as they wean their pup. To what extent males sequentially guard different females as in hooded seals needs to be determined. Males produce sperm about two to six years of age and may not become successful breeders until much later. Females give birth for the first time from three to seven years of age. They give birth to a single young annually. Good data on lactation length are not available nor have analyses of milk composition been done.

conservation status

Not threatened.

significance to humans

None known.

Resources

Books

Berta, Annalisa, and James L. Sumich. Marine Mammals: Evolutionary Biology. New York: Academic Press, 1999.

Blix, Arnoldus S., Lars Walløe, and Øyvind Ultang. Whales, Seals, Fish and Man. Amsterdam: Elsevier, 1995.

Boness, Daryl J. "Life History and Reproductive Strategies." In Marine Mammal Biology, an Evolutionary Approach, edited by A. Rus Hoelzel. Oxford: Blackwell Science, 2002.

King, Judith E. Seals of the World. Ithaca, NY: Comstock, 1983.

Lavigne, David M., and Kit M. Kovacs. Harps & Hoods. Waterloo: University of Waterloo Press, 1988.

Le Boeuf, Burney J. and Richard M. Laws. Elephant Seals. Berkeley: University of California Press, 1994.

Perrin, William F., Bernd Wursig, and J. G. M. Thewissen. The Encyclopedia of Marine Mammals. San Diego: Academic Press, 2002.

Reynolds, John E., III, and Sentiel A. Rommel. Biology of Marine Mammals. Washington, DC: Smithsonian Institution Press, 1994.

Rice, Dale W. Marine Mammals of the World. Lawrence, KS: Allen Press, 1998.

Riedman, Marianne. The Pinnipeds. Berkeley: University of California Press, 1990.

Periodicals

Boness, D. J. "The Evolution of Maternal Care in Pinnipeds." Bio-Science 46 (1996): 1–10.

Kovacs, K. M., and D. M. Lavigne. "Hooded Seal, Cystophora cristata." Mammalian Species 258 (1986): 1–9.

Stewart, B., and Hubner, H. R. "Northern Elephant Seal, Mirounga angustirostris." Mammalian Species 449 (1993): 1–10.

Thomas, J. "Baikal Seal, Phoca sibirica." Mammalian Species 188 (1982): 1–6.

Daryl J. Boness, PhD