Overview

Brief Summary

Biology

The Galapagos sea lion is essentially a coastal animal and is rarely found more than 16 kilometres out to sea (2). Individuals are active during the day and hunt in relatively shallow waters (up to about 200 metres deep) where they feed on fish, octopus, and crustaceans. Sea lions and seals are also capable of making extraordinarily deep dives of up to 200 metres for 20 minutes or more, then rapidly surfacing with no ill effects (5). When ashore, the Galapagos sea lions rest on sandy beaches and rocky areas in colonies of about 30 individuals (2). They are extremely gregarious and pack together on the shore even when space is available (2). Each colony is dominated by one bull that aggressively defends his territory from invading bachelor males (5). This territorial activity occurs throughout the year and males hold their territories for only 27 days or so before being displaced by another male (2). Within this territory the bull has dominance over a group of between 5 and 25 cows. The breeding season is not dependant on migration patterns, as seen in other sea lion species, since the Galapagos sea lion remains around the Galapagos Archipelago all year round. In fact the breeding season is thought to vary from year to year in its onset and duration, though it usually lasts 16 to 40 weeks between June and December (2). Births therefore also take place throughout the year, with females coming ashore to give birth to a single pup. Within two to three weeks of giving birth females go into oestrous again and actively solicit a male (2). Gestation lasts around 11 months, though it probably includes a three month period in which implantation of the fertilised egg is delayed while the female nurses her young (2). Like other sea lions this species relies on cooperation within the group. Often, a single adult female will watch over a group of young pups while other mothers are fishing. They are careful to keep the young pups out of deep water where they may be eaten by sharks (6). The bull will also watch out for his "family" by warning them of the presence of a nearby shark with barks, and even occasionally chasing away the intruder (7).
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Description

The Galapagos sea lion is found in the Galapagos Archipelago where it is one of the most conspicuous and numerous marine mammals. Well adapted to its semi-aquatic lifestyle, it has a streamlined body and powerful fins, and as a member of the eared seals (Otariidae family), which includes fur seals and sea lions; this aquatic mammal is able to control its hind flippers independently (2). This adaptation allows it more agility on land than seals, which cannot move their hind limbs independently. Furthermore, unlike the true seals (family Phocidae), the Galapagos sea lion swims using its strong and well developed fore flippers. Adult males are much larger than females and are brown in colour while females are a lighter tan. Adult males are also distinguished by their raised foreheads, and the hair on the crest may be a lighter colour (2). Juvenile Galapagos sea lions are chestnut brown in colour and measure around 75 centimetres at birth (2) (3).
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Distribution

Range Description

Galápagos Sea Lions are found throughout the Galápagos Archipelago on all the major islands and on many smaller islands and rocks. A colony was established in 1986 at Isla de la Plata, just offshore from mainland Ecuador, but this site is not regularly used. Vagrants can be seen from the Ecuadorian coast north to Isla Gorgona in Columbia. There is also a record from Isla del Coco approximately 500 km southwest of Costa Rica, presumably a vagrant.
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Geographic Range

Galapagos sea lions are found scattered amongst the Galapagos Archipelago, which consists of island clusters positioned directly west of Ecuador. These sea lions reside on all the main islands, rocks, and other diminutive islands of this archipelago. Some are also found ranging along Ecuadorian north coast to Isla Gorgona of Columbia. In 1986, a group arrived at Isla de la Plata near the shores of Ecuador. Some were even spotted 500 km southwest of Costa Rica on Isla del Coco.

Biogeographic Regions: pacific ocean (Native )

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Physical Description

Morphology

Physical Description

Galapagos sea lions differ in color depending on sex and whether their coats are wet or dry. The area surrounding the eyes as well as the muzzle of both males and females are lighter in hue than the rest of the body. After being submerged in water, the bull's coat takes on a dark black hue. When dry, the coat is usually dark brown but can range from different shades of brown to gray. Once a bull reaches full maturity, the coat ceases to get any darker, and its back usually turns a light shade of gray. Mature females, adolescent males, and juveniles vary in shade from light brown to tan. Pups experience their initial molt around five months of age, losing the darker coat they were born with.

Galapagos sea lions are sexually dimorphic, with males larger than females. Males tend to have a thicker, stouter neck, shoulders and chest than females, and adult canines are substantially larger and stronger in males. As males grow, their sagittal crest develops more rapidly, leaving a pronounced protrusion on their head. After the male reaches full maturity, the crest ceases to grow, and its forehead becomes steeper due to the pronounced ridge that forms at the back of its eyes. Female Galapagos sea lions have a more elongated, sleek neck and a wider upper body relative to their body size. Females, along with immature sea lions, do not have sagittal crests; their forehead is less defined and adolescents foreheads are almost nonexistent, with virtually a flat head. Galapagos sea lions can weigh between 50 and 250 kg and are often 150 to 250 cm in length.

Range mass: 50 to 250 kg.

Range length: 150 to 250 mm.

Sexual Dimorphism: male larger; sexes colored or patterned differently; sexes shaped differently

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Galápagos Sea Lions are similar in appearance to California Sea Lions, but differ in size, behavior, and skull morphology. Galápagos Sea Lions are sexually dimorphic, with males growing larger than females and having a suite of several secondary sexual characteristics. The degree of sexual dimorphism appears to be less than in California Sea Lions, although few weights and measurements are available for adults to confirm this suggestion.

There is little information on the lengths and weights attained by Galápagos Sea Lions, but they are said to be somewhat smaller than California Sea Lions. Adult males are estimated to weigh up to 250 kg, but this has not been confirmed through direct study. Adult females caring for pups weigh between 50 and 100 kg. Pups of both sexes are born at approximately six kilograms and weaned at approximately 25-40 kg. Pups are born with a brownish-black lanugo coat that fades to pale brown by three to five months. Pups go through their first moult at around five months of age and emerge with the pelage of adult females and juveniles.

Age of maturity for both sexes is estimated to be about 4-5 years. Females produce one pup each year after a gestation of about 11 months, but may abort (or not produce a pup) while still caring for an older offspring (Trillmich and Wolf 2008). Longevity is estimated to be around 15-24 years but the higher ages are not confirmed (Reijnders et al. 1993).

Galápagos Sea Lions are polygynous and males hold territories both on land and in shallow water near shore that they vociferously and aggressively defend. Male tenure on territories usually lasts from ten days to three months. Males may repeatedly be on territory during the drawn out reproductive period. Most copulations occur in the water.

Pupping and breeding take place across an extended period from May through January. Because of the protracted breeding season and extended care provided to the pups (up to 3 years) by females, there are dependent pups on the rookeries year-round. Females may wean pups in 11-12 months in productive years, but most continue to suckle yearlings for a second year. Some females care for a yearling along with a newborn pup. Pups are attended continuously for the first 4-7 days after birth, after which the female goes to sea to feed. With the departure, the female begins a cycle of foraging trips that last 0.5-3 days during the cold season but may last much longer in the warm season. Pups will enter the water and begin to develop swimming skills 1-2 weeks after birth. In some colonies, females return at night to nurse their pup, departing again the next morning (Trillmich 1986). Females and pups recognize each other and reunite based on calls and scent (Trillmich 1981). Galápagos Sea Lion females feed during day and night, in contrast to Galápagos Fur Seals, which primarily feed at night.

Galápagos Sea Lions are non-migratory. They are unafraid of humans when ashore. Haul-out sites can be on rugged shoreline types, including steep rocky shorelines, ledges and offshore stacks, but colonies are mostly on gently sloping sandy and rocky beaches. Sea lions will use shade from vegetation, rocks, and cliffs, and wade into tidal and drainage pools or move into the ocean, as needed during the heat of the day to avoid overheating.

Diving has been studied in four females on Fernandina and about 20 in the centre of the archipelago. The maximum depth of dive recorded was 338 m and maximum duration was 9.8 minutes. Average depth of dives varied between 45 and 150 m and lasted for 3-5 minutes (Villegas-Amtmann et al. in press). At sea they will raft at the surface and rest on their sides with one or more flippers held vertically in the air.

Galápagos Sea Lions prey on sardines in the west and on sardines as well as myctophids and bathylagids together with small squid in the central parts of the archipelago. Galápagos Sea Lions have been seen smashing octopus on the surface of the water, presumably to stun or break them up to facilitate swallowing. During El Niño events even in the west prey includes green-eyes and myctophids, suggesting a change in foraging strategy.

Feral and uncontrolled dogs have been reported to kill sea lion pups. Shark predation is evident from animals seen with injuries and scars from attacks, and killer whales are presumed to be another predator on Galápagos Sea Lions. Interestingly, juvenile and adult Galápagos Sea Lions have been observed to mob Galápagos sharks that approach rookeries.

Systems
  • Terrestrial
  • Marine
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Male Galapagos sea lions can usually be found inland where abundant shade is present, while females occupy different habitats depending on the age of their pups (Wolf et al., 2005). During the day, sea lions can be found on beaches near the water, which they enter throughout the day. At night, they move higher on the beach. Energy costs of locomotion and thermoregulation contribute to habitat use; Galapagos sea lions most frequently occupy areas neighboring the sea that have adequate levels of shade, flat, uncomplicated terrain, and nearby tide pools. Habitat usage also varies with maturity level and sex during the reproductive period, in which sexual separation occurs (Wolf et al., 2005).

Range depth: 186 (high) m.

Average depth: 37 m.

Habitat Regions: saltwater or marine

Aquatic Biomes: temporary pools; coastal ; brackish water

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Depth range based on 58 specimens in 1 taxon.
Water temperature and chemistry ranges based on 37 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 22.546 - 24.804
  Nitrate (umol/L): 2.793 - 6.029
  Salinity (PPS): 33.950 - 34.697
  Oxygen (ml/l): 4.635 - 4.758
  Phosphate (umol/l): 0.495 - 0.797
  Silicate (umol/l): 3.577 - 5.767

Graphical representation

Temperature range (°C): 22.546 - 24.804

Nitrate (umol/L): 2.793 - 6.029

Salinity (PPS): 33.950 - 34.697

Oxygen (ml/l): 4.635 - 4.758

Phosphate (umol/l): 0.495 - 0.797

Silicate (umol/l): 3.577 - 5.767
 
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On land this sea lion prefers sandy or rocky flat beaches where there is vegetation for shade, tide pools to keep cool and good access to calm waters. It also spends much of its time in the cool, fish-rich waters that surround the Galapagos Islands (2) (4).
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Trophic Strategy

Food Habits

Galapagos sea lions usually forage at shallow depths for fish, squid, octopus, and crustaceans. They have been observed smashing octopus on the water's surface, allowing for easier consumption. During El Niño of the 1980s, their primary diet consisted of sardines and myctophids, or lanternfish.

Animal Foods: fish; mollusks

Primary Diet: carnivore (Piscivore , Molluscivore )

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Associations

Ecosystem Roles

Galapagos sea lions are mutualists with lava lizards on Barrington Island. These lizards are attracted to the flies around the sea lions, and  the lava lizards are often found resting on or around Galapagos sea lions. Galapagos sea lions also transport nautical nutrients into the terrestrial ecosystem, moving nutrients in high concentrations to shoreline flora at low elevations (Fariña et al., 2003). Additionally, young Galapagos sea lion can catch disease from ferrel dogs, which also prey on young sea lions.

Ecosystem Impact: creates habitat

Mutualist Species:

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Predation

When in danger, Galapagos sea lions flee from the water, seeking safety on on shore (Barlow, 1974). Sea lion pups risk predation from feral, wild dogs, which are capable of transmitting diseases to the sea lion population. Killer whales and sharks prey on sea lions; those sea lions that escape are often left with with scars and other injuries (Halpin et al., 2009).

Known Predators:

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Life History and Behavior

Behavior

Communication and Perception

Dominant male Galapagos sea lions patrol their territory, warding off intruders, often with a bark. Dominant bulls also touch the muzzle of females of interest (Orr, 1967). Mother and pups recognize each other by their unique scent and vocal calls (Halpin et al., 2009).

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual

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Life Expectancy

Lifespan/Longevity

Galapagos sea lions are estimated to live 15 to 24 years in the wild and 20 years on average

Typical lifespan

Status: wild:
15 to 24 years.

Average lifespan

Status: wild:
20 years.

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Reproduction

Sea lions in the family Otariidae, including Galapagos sea lions, practice polygamy. Little is otherwise known regarding the mating systems of this species.

Mating System: polygynous

Galapagos sea lions have a long breeding season from May to January, as witnessed by the great size variation of Galapagos sea lions within the Galapagos Archipelago. Gestation lasts 11 months, and single pup is born per female during each breeding interval. Male and female pups weigh about 6 kg when born, and they are weaned at 11 to 12 months of age. Galapagos sea lion pups are partially independent between 12 and 24 months, while still returning to nurse from time to time (Aurioles and Trillmich, 2008; Halpin et al., 2009; Orr, 1967). The age of sexual maturity for both male and female Galapagos sea lions is between 4 and 5 years of age (Aurioles and Trillmich, 2008).

Breeding interval: Galapagos sea lions breed once yearly.

Breeding season: Galapagos sea lions breed between May and January.

Average number of offspring: 1.

Average gestation period: 11 months.

Average birth mass: 6 kg.

Average weaning age: 11 to 12 months.

Average time to independence: 12 to 24 months.

Average age at sexual or reproductive maturity (female): 4 to 5 years.

Average age at sexual or reproductive maturity (male): 4 to 5 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Mother Galapagos sea lions have a close bond with their pups. Mothers attend to their pups continuously for 6 to 7 days after birth, after which they feed in the sea, returning at night to continue feeding their young. Mother and pups recognize each other by their unique scent and vocal calls (Halpin et al., 2009). Female sea lions nurse only one pup at a time, until they give birth to the next pup. Some females allow both her yearling and pup to nurse simultaneously. If the female does not bare another pup, then the first can nurse for up to three years (Trillmich, 1981).

Parental Investment: female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A2a

Version
3.1

Year Assessed
2008

Assessor/s
Aurioles, D. & Trillmich, F. (IUCN SSC Pinniped Specialist Group)

Reviewer/s
Kovacs, K. & Lowry, L. (Pinniped Red List Authority)

Contributor/s

Justification
Due to its small-scale occurrence and small, fluctuating population size, and suggested decline of 50% over the last 30 years the Galápagos Sea Lion should be classified as Endangered.

IUCN Evaluation of the Galápagos Sea Lion, Zalophus wollebaeki
Prepared by the Pinniped Specialist Group


A. Population reduction Declines measured over the longer of 10 years or 3 generations
A1 CR > 90%; EN > 70%; VU > 50%
Al. Population reduction observed, estimated, inferred, or suspected in the past where the causes of the reduction are clearly reversible AND understood AND have ceased, based on and specifying any of the following:
(a) direct observation
(b) an index of abundance appropriate to the taxon
(c) a decline in area of occupancy (AOO), extent of occurrence (EOO) and/or habitat quality
(d) actual or potential levels of exploitation
(e) effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.

Age-structure data are not available for the Galápagos Sea Lion population so the generation time cannot be calculated precisely. However, with sexual maturity attained at 5-6 years of age and a maximum longevity of approximately 20 years, the average age of reproducing individuals should be around 10 years. A population reduction of 50% of Galápagos Sea Lions has been estimated over the past 30 years. This meets the criterion for Vulnerable.

A2, A3 & A4 CR > 80%; EN > 50%; VU > 30%
A2. Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.

A population reduction of Galápagos Sea Lions has been estimated in the past 30 years. The population is protected within a National Park and the reasons for the reduction are not clearly understood. This decline hence warrants a classification of Endangered.

A3. Population reduction projected or suspected to be met in the future (up to a maximum of 100 years) based on (b) to (e) under A1.

A population reduction of Galápagos Sea Lions is suspected in the future because of increased anthropogenic influences (particularly fisheries interactions). The likely degree of population reduction attributable to this threat in the future cannot, however, be projected with any confidence.

A4. An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and the future, and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.

A population reduction of around 50% of Galapagos sea lions has been estimated over the past 30 years.

B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1. Extent of occurrence (EOO): CR < 100 km²; EN < 5,000 km²; VU < 20,000 km²

The EOO of Galápagos Sea Lions is approximately > 138 000 km².

B2. Area of occupancy (AOO): CR < 10 km²; EN < 500 km²; VU < 2,000 km²

The AOO of Galápagos Sea Lions is > 120,000 km².

AND at least 2 of the following:
(a) Severely fragmented, OR number of locations: CR + 1; EN < 5; VU < 10
(b) Continuing decline in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals.
(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations; (iv) number of mature individuals.

C. Small population size and decline
Number of mature individuals: CR < 250; EN < 2,500; VU < 10,000

The current abundance of Galapagos sea lions is roughly known and estimated to be about 20,000.

AND either C1 or C2:
C1. An estimated continuing decline of at least: CR = 25% in 3 years or 1 generation; EN = 20% in 5 years or 2 generations; VU = 10% in 10 years or 3 generations (up to a max. of 100 years in future)
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR < 50; EN < 250; VU < 1,000
or
(a ii) % individuals in one subpopulation: CR = 90?100%; EN = 95?100%; VU = 100%
(b) Extreme fluctuations in the number of mature individuals.

D. Very small or restricted population
Number of mature individuals: CR < 50; EN < 250; VU < 1,000 AND/OR restricted area of occupancy typically: AOO < 20 km² or number of locations < 5

E. Quantitative analysis
Indicating the probability of extinction in the wild to be: Indicating the probability of extinction in the wild to be: CR > 50% in 10 years or 3 generations (100 years max.); EN > 20% in 20 years or 5 generations (100 years max.); VU > 10% in 100 years

There has been no quantitative analysis of the probability of extinction for Galápagos Sea Lions.

Listing recommendation ? Past estimates of Galápagos Sea Lion abundance in 1977-1978 suggested a total population size of about 40,000. Current abundance is estimated around 20,000. The population is protected with a National Park and the cause of the decline is unknown. Thus, Galápagos Sea Lions qualify for listing as Endangered under IUCN criterion A2a.

History
  • 1996
    Vulnerable
  • 1996
    Vulnerable
    (Baillie and Groombridge 1996)
  • 1996
    Vulnerable
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There are an estimated 20,000 to 50,000 individuals of Galapagos sea lions found mainly in the Galapagos Archipelago. The archipelago is part of an Ecuadorian National Park, which is enclosed by a marine resources reserve. Tourism of the park does persist largely, but is carefully monitored to deter any disturbances (Halpin et al., 2009). El Niño of the early 1980’s greatly affected sea lion populations, causing dozens of yearlings to die, and decreasing the pup fecundity for the following year (Trillimich and Limberger, 1985).

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: endangered

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Status

Classified as Endangered (EN) on the IUCN Red List (1).
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Population

Population
The population fluctuates between 20,000 and 40,000 animals. A census in 1978 suggested a population size of about 40,000, but a recent survey in 2001 ? found a 50% decline from this earlier estimate (Alava and Salazar 2006). Methodological differences might exist between counts over this period, but the marked decline suggested is cause for serious concern.

Population Trend
Decreasing
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Threats

Major Threats
The population fluctuates widely due to die-offs and cessation of reproduction during El Niño events, when marine productivity collapses. Irruptions of a sea lion epidemic of unknown causation have occurred during El Niño events, adding to the stress on individuals from starvation. Feral dogs which occasionally prey on sea lions could transmit various diseases to the population, but frequent direct contact between sea lions and domestic dogs in the settlements on San Cristobal, Santa Cruz and Isabela present the greatest danger of disease transmission. The population seems to have declined from a 1978 census until today by an estimated 50% or more (Alava and Salazar 2006) and the reasons for this may partly lie in repeated strong El Niño events but are not clearly understood.
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The Galapagos sea lion faces various threats. In the 19th century, sea-lions worldwide were hunted for their meat, skin and oil. The hunting of some sea-lions, including the Galapagos species, has now been banned and populations have recovered (2). Galapagos sea lions are still vulnerable to human activity as their inquisitive and social nature means they are more likely to approach areas inhabited by humans. This brings them into contact with fishing nets, hooks and human waste, all of which can be fatal (6). There are also problems resulting from the increase in numbers of deep-water tuna and billfish fisheries as these sea-lions become victims of bycatch (7). Research indicates that the majority of these incidents (67 percent) involve juveniles, probably due to their more curious and playful nature (7). These marine mammals are also negatively affected by the phenomenon El Niño. During El Niño 1997 and 1998, Galapagos sea lion populations of the main colonies declined by 48 percent. Many sea lions migrated and, amongst those that stayed in the Galapagos Archipelago, there was high mortality due to starvation (7). A viral disease, known as sea lion pox, is another threat to this marine mammal (5). The illness is spread by mosquitoes and causes paralysis, which in turn prevents the sea lion from feeding and may result in death.
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Management

Conservation Actions

Conservation Actions
The Galápagos Sea Lion population lives in the Galápagos Archipelago, which is an Ecuadorian National Park surrounded by a marine resources reserve. Tourism occurs on a large scale but is controlled to protect wildlife from disturbance.
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Conservation

The Galapagos sea lion occurs in one of the most biologically diverse areas of the world. The Galapagos Islands have long been studied and protected and were influential in the formulation of Darwin's theory of evolution by natural selection. Most recently, in March 1998, a 133,000 square kilometres area was designated as the Galapagos Marine Reserve, making it one of the world's largest protected areas. Detailed conservation and research programmes have been developed, which focus on studying the islands' ecology, the effects of environmental fluctuations on species and the effects of humans on wildlife. These measures have to some extent protected this sea lion, especially from hunting. The Charles Darwin Research Centre has implemented an ecological monitoring project of the Galapagos sea-lion to determine the state and abundance of the sea lions. This project also studies the ongoing threats to this mammal and has developed simple rescue methods for injured or caught sea lions. Elsewhere in the world, sea lions are suffering dramatic population declines for unknown reasons, and so conservation measures like these, which both monitor and protect the sea lion, are invaluable in the future of the Galapagos sea lion (7).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

There are no known adverse effects of Galapagos sea lions on humans.

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Economic Importance for Humans: Positive

Galapagos sea lions may draw in tourists as they are endemic to the Galapagos islands (Aurioles and Trillmich, 2008).

Positive Impacts: ecotourism

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Galápagos sea lion

The Galápagos sea lion (Zalophus wollebaeki) is a species of sea lion that exclusively breeds on the Galápagos Islands and – in smaller numbers – on Isla de la Plata (Ecuador). Being fairly social, and one of the most numerous species in the Galápagos archipelago, they are often spotted sun-bathing on sandy shores or rock groups or gliding gracefully through the surf. Their loud bark, playful nature, and graceful agility in water make them the "welcoming party" of the islands.

Taxonomy[edit]

This species was first described by E. Sivertsen in 1953. This species has been considered a subspecies of Zalophus californianus (called Z. c. wollebaeki) by many authors. But recent genetic data supports the Z. wollebaeki to be a separate species.[1] The species belongs to the family Otariidae and genus Zalophus.

Physical characteristics[edit]

Head and ear detail
Mother and baby at North Seymour Island.

Slightly smaller than their Californian relatives, Galápagos sea lions range from 150 to 250 cm (59 to 98 in) in length and weigh between 50 to 250 kg (110 to 550 lb), with the males averaging larger than females.[2] Adult males also tend to have a thicker, more robust neck, chest, and shoulders in comparison to their slender abdomen. Females are somewhat opposite males, with a longer, more slender neck and thick torso. Once sexually mature, a male’s sagittal crest enlarges, forming a small, characteristic bump-like projection on their forehead. Galápagos sea lions, compared to California sea lions, have a slightly smaller sagittal crest and a shorter muzzle.[3] Adult females and juveniles lack this physical characteristic altogether with a nearly flat head and little or no forehead.

Both male and female sea lions have a pointy, whiskered nose and somewhat long, narrow muzzle. The young pups are almost dog-like in profile. Another characteristic that defines the sea lion are their external ear-like pinnae flaps which distinguish them from their close relative with which they are often confused, the seal. The foreflippers have a short fur extending from the wrist to the middle of the dorsal fin surface, but other than that, the flippers are covered in black, leathery skin. Curving posteriorly, the first digit of the flipper is the largest, giving it a swept-back look. At the end of each digit is a claw, usually reduced to a vestigial nodule that rarely emerges above the skin. Although somewhat clumsy on land with their flippers, sea lions are amazingly agile in water. With their streamlined bodies and flipper-like feet, they easily propel themselves through crashing surf and dangerously sharp coastal rocks. They also have the ability to control their flippers independently and thus change directions with ease, and they have more control over their body on land.

When wet, sea lions are a shade of dark brown, but once dry, their color varies greatly. The females tend to be a lighter shade than the males and the pups a chestnut brown. Born with a longer, brownish-black lanugo, a pup's coat gradually fades to brown within the first five months of life. At this time, they undergo their first molt, resulting in their adult coat. The age of maturity for Galápagos sea lions is estimated at about 4–5 years.[4] The total life span of Galapagos Sea Lions is estimated to be at 15–24 years.[5]

Distribution[edit]

Galápagos sea lions can be found on each of the different islands of the Galápagos archipelago. They have also colonized just offshore the mainland Ecuador at Isla de la Plata, and can be spotted from the Ecuadorian coast north to Isla Gorgona in Colombia. Records have also been made of sightings on Isla del Coco which is about 500 km southwest of Costa Rica. The population on Isla del Coco is thought to be a vagrant population, while the population in the Galápagos archipelago is considered native.[2]

Diet and feeding patterns[edit]

Feeding mostly on sardines, Galápagos sea lions sometimes travel 10 to 15 kilometers from the coast over the span of days to hunt for their prey. This is when they come into contact with their biggest predators: sharks and killer whales. Injuries and scars from attacks are often visible. During el Niño events, which occurs when the water temperature changes and causes climate change in the Pacific,[6] more green-eyes and myctophids are consumed due to a decrease in sardine population. El Nino caused many population decreases by changing the sea lion's availability for food, causing these Galapagos Sea Lions to be listed as endangered.[6]

Behavior and male competition[edit]

Galápagos sea lions are especially vulnerable to human activity. Their inquisitive and social nature makes them more likely to approach areas inhabited by humans, and thus come into contact with human waste, fishing nets, and hooks. They occupy many different shoreline types, from steep, rocky cliff sides to low-lying sandy beaches. To avoid overheating during the day, sea lions will take refuge from the sun under vegetation, rocks, and cliffs.

Not only are sea lions social, they are also quite vocal. Adult males often bark in long, loud and distinctive repeated sequences. Females and juveniles do not produce this repetitive bark, but both sexes the younger pups will growl. From birth, a mother sea lion recognizes her pup’s distinct bark and can pinpoint it from a crowd of 30 or more barking sea lions.

The Galapagos Sea Lion male has two types’ territorial males and non-territorial males. There are clear cut differences in behavior from territorial males and non-territorial males, the first being the territorial males vocalized at higher rates than non-territorial males and the onset of vocalization tends to be higher. Vocalization is important to territorial males because it plays a key role in sexual selection and helps ward off intruding non territorial males into their harem. Most vocalizations made by territorial males are long range and not directed to anything specific.

On land, sea lions form colonies at their hauling-out areas. Adult males, bulls, are the head of the colony, growing up to 7 ft (2;m) long and weighing up to 800 pounds (360 kg). As males grow larger, they fight to win dominance of a harem of between five and 25 cows, and the surrounding territory. Swimming from border to border of his colony, the dominant bull jealously defends his coastline against all other adult males. While patrolling his area, he frequently rears his head out of the water and barks, as an indication of his territorial ownership. The neighboring territorial males tend to display a “dear enemy effect”, where territorial males decrease vocalization and aggression.Through repetitive encounters with other territorial bulls, males displayed reduced aggression and stored key information about a neighbor’s strength as an adversary.

The average dominant bull holds his territory for only a few months, until he is challenged by another male. On land, these fights start by two bulls stretching out their necks and barking in attempt to test each other’s bravery. If this is not enough to scare the opponent off, they begin pushing each other and biting around the neck area. If males were not equipped with thick, muscular necks, their vital organs would be easily damaged during these fights. Blood is often drawn, however, and many male sea lions have battle scars due to these territorial competitions. Losers are dramatically chased far from their territory by the new dominant bull with much splashing.

Because there is only one male in each harem, there is always a surplus of “bachelor” male sea lions. They usually congregate fairly peaceably on less favorable areas of the coastline in “bachelor colonies”. One of the most commonly known is atop the cliffs of the South Plaza Island of the Galápagos chain. Because the dominant male of the harem cannot feed while defending his colony, he eventually becomes too tired and weak, and is overpowered by a well-nourished, fresh bull.The territorial males that lose their territory but decide to stay on the island tend to vocalize less and have a lowered fighting ability, due to fasting.

Breeding[edit]

A young Galápagos sea lion

Breeding takes place from May through January. Because of this prolonged breeding season and the extensive care required by the pups from their mother, there are dependent pups in the colonies year round. Each cow in the harem has a single pup born a year after conception. After about a week of continuous attention from birth, the female returns to the ocean and begins to forage, and just a week after that, the pup will follow her and begin to develop its swimming skills. When the pup is two to three weeks old, the cow will mate again. The mothers will take the young pups with them into the water while nursing until around the 11th month, when the pups are weaned from their mother’s milk and become dependent on their own hunting skill.

The static and social interaction between mother-offspring pairs is a central social unit in most mammalian groups, as well as these sea lions.[7] The cow will nurture a pup for up to three years. In that time, the cow and the pup will recognize each other's bark from the rest of the colony. Within the colony, sea lion pups live together in a rookery. Pups can be seen together napping, playing, and feeding. It is not uncommon to see one cow 'baby-sitting' a group of pups while the other cows go off to feed.

Many mammals synchronize their pregnancies to insure a greater infant survival rate, but not the Zalophus Wollebaeki.[8] The Zalophus Wollebaeki is different from most mammals since they do not synchronize, which can be a major reason why they are becoming extinct.[8] Higher infant mortality rate is the effect caused by the lack of synchrony between the mother sea lions. Plausible reasons for this low synchrony could be the absence of strong photoperiodic change throughout the year, which is thought to regulate embryonic diapause, or adaptation to an environment with variable productivity and prey availability, or both.[8]

Threats and status[edit]

The majority of the Galápagos population is protected, as the islands are a part of the Ecuadorian National Park surrounded by a marine resources reserve. Although the Galápagos Islands are a popular tourist destination, strict rules protect all wildlife from disturbance. Fluctuating between 20,000 and 50,000 sea lions, the population does have a few threats. During el Niño events, the population tends to decrease due to die-offs, cessation of reproduction, and collapses in marine life on which the seals are dependent. Sharks and killer whales are the main predators to the sea lion.

References[edit]

Notes[edit]

  1. ^ a b Aurioles, D. & Trillmich, F. (2008). Zalophus wollebaeki. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 30 January 2009.
  2. ^ a b http://www.iucnredlist.org/details/41668/0
  3. ^ Wolf, J. B. W., Tautz, D. and Trillmich, F. 2007. Galapagos and Californian sea lions are separate species: genetic analysis of the genus Zalophus and its implications for conservation management. Frontiers Zoology 4: doi:10.1186/1742-9994-4-20.
  4. ^ Aurioles, D. & Trillmich, F. (IUCN SSC Pinniped Specialist Group) 2008. Zalophus wollebaeki. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1. <http://www.iucnredlist.org/details/41668/0>.
  5. ^ Reijnders et al. 1993
  6. ^ a b Páez-Rosas, Diego, and David Aurioles-Gamboa. "Alimentary Niche Partitioning In The Galapagos Sea Lion, Zalophus Wollebaeki." Marine Biology 157.12 (2010): 2769-2781. Academic Search Premier. Web. 24 Oct. 2013. [1]
  7. ^ Wolf, Jochen B. W., and Fritz Trillmich. "Beyond Habitat Requirements: Individual Fine-Scale Site Fidelity In A Colony Of The Galapagos Sea Lion (Zalophus Wollebaeki) Creates Conditions For Social Structuring." Oecologia 152.3 (2007): 553-567. OmniFile Full Text Mega (H.W. Wilson). Web. 24 Oct. 2013.[2]
  8. ^ a b c VILLEGAS-AMTMANN, S., S. ATKINSON, and D. P. COSTA. "Low Synchrony In The Breeding Cycle Of Galapagos Sea Lions Revealed By Seasonal Progesterone Concentrations." Journal Of Mammalogy 90.5 (2009): 1232-1237. Academic Search Premier. Web. 24 Oct. 2013. [3]

Further reading[edit]

  1. Kunc, Hansjoerg P., and Jochen B. W. Wolf. "Seasonal Changes Of Vocal Rates And Their Relation To Territorial Status In Male Galápagos Sea Lions ( Zalophus Wollebaeki)." Ethology 114.4 (2008): 381-388. Academic Search Premier. Web. 24 Oct. 2013. [4].
  2. Meise, Kristine, Oliver Kruger, Paolo Piedrahita, and Fritz Trillmich. "Site Fidedility of Male Galapagos Sea Lions: A Lifetime Perspective." 67.6 (Jun 2013): 1001+. Web of Science. Web. 24 Oct. 2013.[5].
  3. Wolf, Jochen B., et al. "Males in the Shade: Habitat use and Sexual Segregation in the Galápagos Sea Lion (Zalophus Californianus Wollebaeki)." Behavioral Ecology and Sociobiology 59.2 (2005): 293-302. ProQuest. Web. 24 Oct. 2013. [6].

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