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Cystophora cristatahooded seal

By Samantha Salman

Geographic Range

Hooded seals are generally found from 47° to 80° N latitude. They occur along the eastern coast of North America north of Maine. Hooded seals also reach the western tip of Europe, along the coast of Norway. They are mainly concentrated around Bear Island, Norway, Iceland, and northeast Greenland. In rare cases they have been found in Siberia. (Kovacs and Lavigne, 1986; Perrin, et al., 2002)

Habitat

Hooded seals are found in coastal areas of Atlantic and Arctic Oceans. They are successful divers that spend much of their time in the water. They usually dive to a depth of 600 m but can go as deep as 1000 m. When they are on land they usually occur in areas with significant ice cover or made up of ice packs. They migrate annually in order to stay in areas where there is drifting pack ice. (Kovacs and Lavigne, 1986; Perrin, et al., 2002)

  • Terrestrial Biomes
  • icecap
  • Range depth
    100 to 1000 m
    328.08 to 3280.84 ft
  • Average depth
    600 m
    1968.50 ft

Physical Description

Hooded seals have blue-gray pelage with black spots over the body. The front of the face is black and this coloration extends posteriorly to just behind the eyes. Their limbs are rather small in proportion to their body, but are powerful nonetheless, making these seals excellent swimmers and divers. Hooded seals exhibit marked sexual dimorphism. Males are slightly longer than females, and reach 2.5 m in length; females average 2.2 m. The more significant difference between the sexes is weight. Males weigh up to 300 kg while females only weigh up to 160 kg. Also unique to males is the inflatable hood and nasal septum. ("Cystophora cristata, Hooded Seal", 2007; Kovacs and Lavigne, 1986)

Hooded seals get their name from the inflatable “hood” on the top of the heads of males. The hood is not present until males are about 4 years old. When the hood is deflated, it hangs down over the upper lip. Males inflate this red, balloon-like nasal septum until it protrudes out of one nostril. Males use this nasal sac for aggressive display and also to get the attention of females.

Hooded seals have many characteristics that differentiate them from other phocids. They have the largest nostrils in the family. The skull is short with a wide snout. They also have a palate that projects posteriorly further than any other seal. One-third of the nasal bone extends beyond the edge of the maxilla. Their incisor formula is unique, with two upper and one lower incisor. The teeth are small and the tooth row is narrow. The dental formula is I 2/1, C 1/1, PC 5/5. Hooded seals have light and dark bands of cementum in the canines that can be used to determine age.

At birth the coloring of young is silver on the dorsal side, without spots, and blue-gray on the ventral side, which accounts for their nickname ”bluebacks.” Young are 90 to 105 cm in length when born and average 20 kg. Around age 1, differences between males and females can be observed; males begin growing larger in weight and length.

  • Range mass
    160 to 300 kg
    352.42 to 660.79 lb
  • Range length
    2.2 to 2.5 m
    7.22 to 8.20 ft

Reproduction

During the short time that the mother is giving birth and nursing her pup, several males will be in close proximity to her in order to obtain mating rights. At this time many males will aggressively threaten each other using their inflated nasal sac and even push each other out of the breeding area. Males do not typically defend personal territories; they only defend the area where there is a receptive female. A successful male will then mate with the female in the water. Once returning to land he will search for another female. Mating occurs typically through April and June. ("Cystophora cristata", 2009; Kovacs and Lavigne, 1986)

Females reach the age of sexual maturity between 2 and 9 years old and it is estimated that most females give birth to their first young at around 5 years of age. Males reach sexual maturity a little later around 4 to 6 years old but often do not mate until much later. Females give birth to one young at a time through March and April. The gestation period is 240 to 250 days. During this time the fetus - unlike those of other seals - sheds its lanugo (a covering of fine soft hair that is replaced thicker pelage) in the uterus. These young are precocial and at birth are able to move about and swim with ease. They are independent and left to fend for themselves immediately after they have been weaned. ("Cystophora cristata, Hooded Seal", 2007; "Seal Conservation Society", 2001; Kovacs and Lavigne, 1986)

  • Breeding interval
    Hooded seals breed once a year.
  • Breeding season
    Hooded seals breed from April to June.
  • Range number of offspring
    1 to 1
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    240 to 250 days
  • Range weaning age
    5 to 12 days
  • Range age at sexual or reproductive maturity (female)
    2 to 9 years
  • Average age at sexual or reproductive maturity (female)
    3.2 years
  • Range age at sexual or reproductive maturity (male)
    4 to 6 years

Hooded seals have the shortest nursing period of any mammal, from 5 to 12 days. The milk of the female is rich in fat, which makes up about 60 to 70% of its content and allows the pup to double in size during its short nursing period. During this same period, the mother loses 7 to 10 kg each day. Females are protective of their pup during their short weaning interval. They fight potential predators, including other seals and humans. Males do not invest energy in defending their young. Since young are precocial at birth and already able to crawl and swim, little is done to help raise them. (Kovacs and Lavigne, 1986)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The expected maximum lifespan of hooded seals is 35 years. In this sexually dimorphic species the differences in body size among males and females result in differences in longevity. In hooded seals males are larger and have shorter lifespans. The mortality rate of adults is 7 to 15% a year. One cause of death is known to be infections from the parasitic heartworm, Dipetalonema spirocauda. Before there were restrictions on hunting, humans were the main cause of death in hooded seals. Captive hooded seals have been reported to die from tuberculosis and cranial infections. (Kovacs and Lavigne, 1986)

  • Typical lifespan
    Status: wild
    35 (high) years

Behavior

Hooded seals are mostly solitary animals, except when they are breeding and molting. During these two periods the seals fast. They congregate annually in July near Denmark Strait when they are about to molt. They then gather at different sites when they are about to breed. Most of what is known about them has been learned during these congregating periods. The inflatable nasal sac is often displayed when males feel threatened or want to attract the attention of a female.

Dives of hooded seals generally last 30 minutes, but longer dives have been recorded. When hooded seals dive, they do not elicit a shivering mechanism when under hypothermic conditions. This is because shivering would cause an increase in need for oxygen and thus reduce the amount of time they can spend under water. When on land, seals do shiver in response to cold, but it is slowed or stopped altogether once the seal is submerged. ("Cystophora cristata", 2009; Kovacs and Lavigne, 1986; Kvadsheim, et al., 2005)

Home Range

Hooded seals live solitary lives and do not compete for territory or social hierarchy. Hooded seals are migratory and follow a specific movement pattern every year in order to stay close to drifting pack ice. In spring, hooded seals concentrate in three locations: the Gulf of St. Lawrence, Davis Strait, and West Ice. During the summer they move to two locations, the southeast and northeast coasts of Greenland. After they molt, hooded seals disperse broadly and make long excursions to the north and south in the North Atlantic during the autumn and winter months before they reconvene in spring. (Kovacs and Lavigne, 1986; Perrin, et al., 2002)

Communication and Perception

Hooded seals are able to make vocalizations such as roars that can be heard easily on land. However, their most important form of communication is produced from the hood and septum. They are able to produce pulses ranging from 500 to 6 Hz, these sounds can be heard on land and in the water. They are often seen moving their inflated hood and nasal septum up and down, which can create sounds described as “pings” and “whooshes”. This method of communication can serve as male display for females but also serve as threats. (Kovacs and Lavigne, 1986; Perrin, et al., 2002)

Food Habits

Hooded seals eat a variety of marine prey, especially fish, such as redfish, herring, polar cod, and flounder. They also feed on octopus and shrimp. Some research indicates that during the winter and autumn hooded seals feed more on squid and switch to primarily fish in the summer, especially polar cod. Pups first begin feeding near the shore and eat mainly squid and crustaceans. When Arctic algae and phytoplankton bloom, their energy is transferred to fatty acids. These food sources are eaten by herbivores and make their way up the food chain to the top predators like the hooded seal. The fatty acids that begin at the bottom of the food chain are then stored in the blubber of the seals. This blubber is sustained throughout the autumn and winter and used as an energy resource in the summer during the molting and breeding season when fasting occurs. (Falk-Petersen, et al., 2009; Haug, et al., 2007; Kovacs and Lavigne, 1986)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

In recent times, the major predators of hooded seals have been humans. The sealing industry began in the 18th century and these mammals were hunted for 150 years without any restrictive laws. More than 500,000 seals (hooded and harp seals) were caught per year between 1820 and 1860. At first, sealing was popular because there was a demand for oil and leather. After the 1940s, seals began to be hunted for their fur and one of the most prized species was the hooded seal, considered four times more valuable than other seals. A quota to limit hunting was introduced in 1971 and was set at 30,000. ("Cystophora cristata", 2009; Kovacs and Lavigne, 1986; Perrin, et al., 2002)

Natural predators of hooded seals include sharks, polar bears, and killer whales. Polar bears mainly feed on harp and bearded seals but will hunt hooded seals when they are breeding on ice and are more visible, vulnerable targets.

Ecosystem Roles

Hooded seals often find themselves the host of parasitic worms, such as heartworms, Dipetalonema spirocauda. Often these parasites result in shortened lifespans. Hooded seals are predators of many fishes, such as polar cod, squid, and various crustaceans. They are preyed on by sharks, orcas, and polar bears. (Kovacs and Lavigne, 1986; Perrin, et al., 2002)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Hooded seals have played an important role in subsistence for the natives of Greenland and Canada who hunt these seals for a source of food. They have also provided valuable goods including leather, oil, and fur. However excessive demand of these goods have negatively impacted populations of hooded seals. ("Cystophora cristata", 2009; Kovacs and Lavigne, 1986)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no negative effects of hooded seals on humans.

Conservation Status

Hooded seals were hunted in high numbers starting in the 18th century. The popularity of their pelts, especially of the “bluebacks”, which are pup pelts, resulted in a rapid decline of populations. After World War II the hunt for hoodeds seals increased, resulting in concern that they would become endangered. In 1958 laws were introduced, followed by quotas in 1971. Recent efforts include treaties and agreements, banning of hunting in areas such as the Gulf of St. Lawrence, and bans on importation of seal products. Despite these measures hooded seal populations are still on the decline for unknown reasons. ("Cystophora cristata", 2009)

Other Comments

Hooded seals do not have a very complete fossil record. One of the first few fossils found was from Anvers, Beligum in 1876, which dated to the Pliocene. In 1983 a paper was published claiming there were some fossils found in North America thought to be from Cystophora cristata. Of the three accounts, the most creditable discovery was from a sewer excavation in Maine. A scapula and humeri were found among other bones and thought to date to the post-Pleistocene. Of two other accounts, one was later reassigned to another species and the other left unsolved. (Folkow, et al., 2008; Kovacs and Lavigne, 1986; Ray, 1983)

Hooded seals are able to dive for long periods of time due to their tolerance of hypoxia. Research discovered that oxygen delivery to the brain is boosted by an increase in density of brain capillaries. More importantly, these seals have neurons that are inherently hypoxia tolerant. Studies showed that their neurons were able to discharge four times longer than those of mice in hypoxic conditions. (Folkow, et al., 2008; Kovacs and Lavigne, 1986; Ray, 1983)

Contributors

Samantha Salman (author), Case Western Reserve University, Darin Croft (editor, instructor), Case Western Reserve University, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

food

A substance that provides both nutrients and energy to a living thing.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

piscivore

an animal that mainly eats fish

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

polygynous

having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

References

2007. "Cystophora cristata, Hooded Seal" (On-line). MarineBio. Accessed November 29, 2009 at http://marinebio.org/species.asp?id=304.

2009. "Cystophora cristata" (On-line). IUCN Red List of Threatened Species. Version. Accessed November 20, 2009 at http://www.redlist.org/apps/redlist/details/6204/0.

2001. "Seal Conservation Society" (On-line). Hooded Seal. Accessed December 01, 2009 at http://www.pinnipeds.org/species/hooded.htm.

Falk-Petersen, S., T. Haug, H. Hop, K. Nilssen, A. Wold. 2009. DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY. DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, Vol. 56 Issue 21-22: 2080-2086.

Folkow, L., J. Ramirez, S. Ludvigsen, N. Ramirez, A. Blix. 2008. Remarkable neuronal hypoxia tolerance in the deep-diving adult hooded seal. Neuroscience Letters, Vol. 446 Issue 2-3: 147-150.

Haug, T., K. Nilssen, L. Lindblom, U. Lindstrom. 2007. Diets of hooded seals (Cystophora cristata) in coastal waters and drift ice waters along the east coast of Greenland. Marine Biology Research, Vol. 3 Issue 3: 123-133.

Kovacs, K., D. Lavigne. 1986. Cystophora cristata. Mammalian Species, 258: 1-9. Accessed November 29, 2009 at http://www.science.smith.edu/departments/Biology/VHAYSSEN/msi/default.html.

Kvadsheim, P., L. Folkow, A. Blix. 2005. Inhibition of shivering in hypothermic seals during diving. AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY, Vol. 289 Issue 2: R326-R331.

Perrin, W., B. Wursig, J. Thewissen. 2002. Encyclopedia of Marine Mammals. San Diego, CA: Academic Press.

Ray, C. 1983. Hooded Seal, Cystophora cristata: Supposed Fossil Records in North America. American Society of Mammalogists, Vol. 64 No. 3: 509-512.

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