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Arctocephalus galapagoensisGalápagos fur seal

By Charles Kolodziejski

Geographic Range

As suggested by the common name, Galapagos fur seals (Arctocephalus galapagoensis) are found primarily on the shores of, and in the waters immediately surrounding, the Galapagos Islands. During the breeding season, populations are observed in the northern and western parts of the Galapagos Islands. Galapagos fur seals are non-migratory. (Clark, 1979; Nowak, 1999) (Clark, 1979; Nowak, 1999)

Habitat

Galapagos fur seals are found in the Galapagos Archipelago, a group of islands located about 1000 km off of the coast of Ecuador, which have been formed by a multitude of volcanic eruptions. The Galapagos Islands are almost directly on the equator and are characterized by two seasons: a cool season (August to November) and a warm season (December to July). Being near the equator, average sea temperatures are relatively high; they range from an average of 22 degrees Centigrade during the cool season to 25 degrees Centigrade during the warm season. To escape high temperatures, Galapagos fur seals frequently take shelter in the shade of boulders, in caves, and under lava ledges. (Limberger et al., 1986) When Galapagos fur seals venture out into the deep waters of the Pacific Ocean they swim in the waters of the Humboldt Current and make dives of typically less than 30 meters (Nowak, 1999). (Limberger, et al., 1986; Nowak, 1999)

Physical Description

Male Galapagos fur seals are on average 154 cm in length and weigh 64 kg, while females are 120 cm in length and weigh 27 kg, making Arctocephalus galapagoensis the smallest otariid. The fur of Arctocephalus galapagoensis is a light tan on the stomach and around the mouth and ears. The rest of the fur is colored gray-brown (Nowak, 1999). During lactation and perinatal fasting, female Galapagos fur seals lose about 1.68% of body mass per day and have a metabolic rate 1.1 times higher than the expected metabolic rate according to the Kleiber curve of energetics (Costa and Trillmich, 1988; Trillmich and Kooyman, 2001). (Costa and Trillmich, 1988; Nowak, 1999; Trillmich and Kooyman, 2001)

  • Sexual Dimorphism
  • male larger
  • Range mass
    27 to 64 kg
    59.47 to 140.97 lb
  • Range length
    120 to 154 cm
    47.24 to 60.63 in

Reproduction

Galapagos fur seals are polygynous, meaning that a single male will seek and mate with multiple females. Males establish territories and defend groups of females, but due to environmental factors, they are not very efficient at protecting their females and other males are able to successfully mate on a rival male’s territory (Nowak, 1999). One adult male may mate with 6 to 10 females located within his territory. This is a relatively small number of mates compared to other otariids, but is in part due to the spatial distribution of females within the population (Riedman, 1990; Arnould, 2002). Adult males defend their territories without eating until the physical demands, nutritional needs, or heat becomes so great that they must enter the water. During the El Nino of 1982, adult territorial males were driven to near 100% mortality because the food supply did not provide sufficient energy to sustain the demands of territory defense (Trillmich and Limberger, 1985). (Arnould, 2002; Nowak, 1999; Riedman, 1990; Trillmich and Limberger, 1985)

Galapagos fur seal breeding occurs once a year; the breeding season, August to November, coincides with the cool season in the Galapagos islands. Pregnancy can last about a year, but this may not be a good reflection of the duration of fetal development, because females are thought to undergo a process of delayed implantation (Nowak, 1999; Riedman, 1990). Females give birth to one pup at a time and can resume estrous 5 to 10 days after the birth of a pup or after they also resume foraging trips (Nowak, 1999; Riedman, 1990; Arnould, 2002). However, even though females can resume estrous shortly after giving birth, they often do not become pregnant if they have a pup that still requires milk as the major form of nourishment. The lactation period for adult females is relatively long compared to other otariids; pups are not weaned until they are between the ages of 2 and 3. This long lactation period has been linked to unstable environmental conditions caused by El Nino events (Trillmich and Limberger, 1985). The long lactation period causes sibling conflict if a mother gives birth to a second pup before the first is weaned. In many cases, either the older sibling will kill the younger or the younger sibling will starve to death (Nowak, 1999; Trillmich and Wolf, 2008). (Arnould, 2002; Nowak, 1999; Reijnders, et al., 1993; Riedman, 1990; Trillmich and Limberger, 1985; Trillmich and Wolf, 2008)

Even though young Galapagos fur seals are not weaned until at least the age of 2, pups begin to make trips into the ocean at 6 months and begin to forage for themselves at 12 months. However, pups continue to rely on milk as a major form of nourishment until they are fully weaned and become independent, which typically occurs between the ages of 2 and 3 (Horning and Trillmich, 1997). (Horning and Trillmich, 1997)

Females become sexually mature between 3 to 5 years of age. It takes males slightly longer to become sexually mature and large enough to defend territories, anywhere from 7 and 10 years (Reijnders et al., 1993; Nowak, 1999). At birth a male will typically weigh 3.8 kg, while a female will weigh 3.4 kg (Trillmich, 1986). (Nowak, 1999; Reijnders, et al., 1993; Trillmich, 1986)

  • Breeding interval
    Galapagos fur seals breed once yearly.
  • Breeding season
    Galapagos fur seals breed from August to November.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    11 to 12 months
  • Average gestation period
    213 days
    AnAge
  • Range weaning age
    12 (low) months
  • Average weaning age
    24-36 months
  • Range time to independence
    2 to 3 years
  • Range age at sexual or reproductive maturity (female)
    3 to 5 years
  • Range age at sexual or reproductive maturity (male)
    7 to 10 minutes

Like most mammal species, female Arctocephalus galapagoensis make a substantial investment in their offspring. Weaning does not occur until pups are between 2 to 3 years of age. After the first 5 to 10 days of a pup’s life a mother will divide her time between foraging at sea and spending time with the offspring on shore (Nowak 1999). The extent to which males give direct parental care is not known; there is a possibility that males provide some indirect parental care through territorial defense during the mating season (Arnould, 2002; Riedman, 1990). (Arnould, 2002; Nowak, 1999; Riedman, 1990)

  • Parental Investment
  • altricial
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

On average the lifespan of Galapagos fur seals is about 264 months, or 22 years (Ferguson and Higdon, 2006). (Ferguson and Higdon, 2006)

Behavior

Behaviorally, two things are especially odd about Arctocephalus galapagoensis. First, this is a non-migratory species of otariid that lives and gives birth in a mainly tropical environment. Second, this species spends a large amount of time on land compared to other otariids; as much as 30% of an individual's time may be spent on land. Given these two lifestyle characteristics, Arctocephalus galapagoensis has many behaviors that relate to avoiding the heat from the sun. These behaviors include lying in the shade of boulders, caves, and under lava ledges and also making trips into the ocean (Limberger et al., 1986; Nowak, 1999).

Galapagos fur seals are nocturnal foragers and make foraging trips that typically last about 16 hours. The average dive is between 10 and 30 meters (Nowak, 1999; Reijnders et al., 1993). (Limberger, et al., 1986; Nowak, 1999; Reijnders, et al., 1993)

  • Average territory size
    200 m^2

Home Range

When on land, Arctocephalus galapagoensis lives in large groups, which males attempt to divide up by establishing territories. The territories of male Arctocephalus galapagoensis can reach sizes of up to 200 square meters. Females are usually found in these territories in groups of 6 to 10 individuals per 100 square meters (Nowak 1999). (Nowak, 1999)

Communication and Perception

Galapagos fur seals make two separate vocalizations when foraging at night in the ocean. First, they make a lengthened growl, and secondly, they make a snap or knocking sound. The purpose of these vocalizations is not known, but they are thought to aid in foraging and are not thought to be a form of communication (Merlen, 2000). However, fur seals generally communicate with vocalizations and through visual displays. (Merlen, 2000; Merlen, 2000)

Food Habits

Galapagos fur seals eat fish and various cephalopods off the coast of the Galapagos. Foraging occurs at night, when prey migrate closer to the surface of the water and to a depth where seals can reach them (Nowak, 1999; Horning and Trillmich, 1997). Foraging behavior in Arctocephalus galapagoensis is influenced by the lunar cycle. Foraging trips are much longer during the new moon than during the full moon (Nowak, 1999; Trillmich and Mohren, 1984). Foraging behavior is greatly affected by the tropical storm El Nino. During the El Nino of 1982 the population of Galapagos fur seals was substantially reduced. About 30% of adults and almost all seals under the age of 4 did not survive. El Nino cycles are thought to be responsible for the Galapagos fur seals’ long lactation periods (Nowak, 1999, Limberger and Trillmich, 1985). Pups are weaned between 2 and 3 years of age and are mostly dependent upon their mother before this time (Horning and Trillmich, 1997). (Horning and Trillmich, 1997; Nowak, 1999; Trillmich and Limberger, 1985; Trillmich and Mohren, 1981)

  • Animal Foods
  • fish
  • mollusks

Predation

Occasionally, Galapagos fur seals are preyed on by killer whales (Orcinus orca) and sharks, but more frequently, Galapagos fur seals are threatened by feral dogs living on the islands that they inhabit (Nowak, 1999; Merlen, 2000; Riedman, 1990). (Merlen, 2000; Nowak, 1999; Riedman, 1990)

Ecosystem Roles

The role of Galapagos fur seals in the ecosystem has not been studied as of yet.

Economic Importance for Humans: Positive

There is relatively little interaction between humans and Arctocephalus galapagoensis, but, in the early 20th century, the seals were hunted for fur. Today, Galapagos fur seals are one of the many endemic species of the Galapagos that bring tourism to the islands (Clark, 1979; de Groot, 1983; McElroy, 2003; Nowak, 1999). (Clark, 1979; McElroy, 2003; Nowak, 1999; de Groot, 1983)

Economic Importance for Humans: Negative

There are no known adverse effects of Arctocephalus galapagoensis on humans. However, there may be a negative effect upon the fishing industry due to competition over fish species that Galapagos fur seals eat (DeMaster et al., 2001). (DeMaster, et al., 2001)

Conservation Status

In the early 20th century, Galapagos fur seals were put under the protection of Ecuadorian law because they were hunted almost to extinction by sealers (Nowak, 1999). (Nowak, 1999)

Contributors

Charles Kolodziejski (author), Michigan State University, Barbara Lundrigan (editor), Michigan State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

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.

female parental care

parental care is carried out by females

island endemic

animals that live only on an island or set of islands.

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).

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.

nocturnal

active during the night

piscivore

an animal that mainly eats fish

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

sedentary

remains in the same area

sexual

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

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

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.

References

Arnould, J. 2002. Southern fur seals: Arctocephalus spp.. Pp. 329-410; 726-1150 in W Perrin, B Würsig, J Thewissen, eds. Encyclopedia of Marine Mammals, Vol. 1, 1 Edition. London: Academic Press.

Clark, T. 1979. Mammals in the seas: Pinniped species summaries and report on sirenians. Rome, Italy: Food and Agriculture Organization of the United Nations.

Costa, D., F. Trillmich. 1988. Mass Changes and Metabolism during the Perinatal Fast: A Comparison between Antarctic (Arctocephalus gazella) and Galápagos Fur Seals (Arctocephalus galapagoensis). Physiological Zoology, 61: 160-169.

DeMaster, D., C. Fowler, S. Perry, M. Richlen. 2001. Predation and Competition: The Impact of Fisheries on Marine-Mammal Populations Over the Next One Hundred Years. Journal of Mammalogy, 82: 641-651.

Ferguson, S., J. Higdon. 2006. How Seals Divide up the World: Environment, Life History, and Conservation. Oecologia, 150: 318-329.

Horning, M., F. Trillmich. 1997. Ontogeny of Diving Behaviour in the Galapagos Fur Seal. Behaviour, 134: 1211-1257.

Limberger, D., F. Trillmich, H. Biebach, R. Stevenson. 1986. Temperature regulation and microhabitat choice by free-ranging Galapagos fur seal pups (Arctocephalus galapagoensis). Oecologia, 69: 53-59.

McElroy, J. 2003. Tourism Development in Small Islands across the World. Geografiska Annaler. Series B, Human Geography, 85: 231-242.

Merlen, G. 2000. Nocturnal Acoustic Location of the Galapagos Fur Seal (Arctocephalus galapagoenis). Marine Mammal Science, 16: 248-253.

Nowak, R. 1999. Walker's Mammals of the World. Baltimore and London: The Johns Hopkins University Press.

Reijnders, P., S. Brasseur, J. van der Toorn, P. van der Wolf, I. Boyd, J. Harwood, D. Lavigne, L. Lowry. 1993. Seals, Fur Seals, Sea Lions, and Walrus: Status Survey and Conservation Action Plan. Gland, Switzerland: IUCN.

Riedman, M. 1990. The Pinnipeds: seals, sea lions and walruses. Berkeley and Los Angeles: University of California Press.

Trillmich, F. 1986. Maternal Investment and Sex-Allocation in the Galapagos fur Seal, Arctocephalus galapagoensis. Behavioral Ecology and Sociobiology, 19: 157-164.

Trillmich, F., G. Kooyman. 2001. Field metabolic rate of lactating female Galápagos fur seals (Arctocephalusgalapagoensis): the influence of offspring age and environment. Comparative Biochemistry and Physiology, 129: 741-749.

Trillmich, F., D. Limberger. 1985. Drastic effects of El Nino on Galapagos pinnipeds.. Oecologia, 67: 19-22.

Trillmich, F., W. Mohren. 1981. Effects of the lunar cycle on the Galápagos fur seal, Arctocephalus galapagoensis. Oecologia, 48: 85-92.

Trillmich, F., J. Wolf. 2008. Parent–offspring and sibling conflict in Galápagos fur seals and sea lion. Behavioral Ecology and Sociobiology, 62: 363-375.

de Groot, R. 1983. Tourism and conservation in the Galapagos Islands. Biological Conservation, 26: 291-300.

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