GALAPAGOS SEA LION

 

Male

The Galapagos sea lion is a species of sea lion that breeds on the Galapagos Islands and, in smaller numbers, on Isla de la Plata (Ecuador). Being fairly social, 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. They are the smallest sea lion species.

Distinctive characteristics

Female

Galapagos sea lion are similar in appearance to California sea lions, but differ in size, behavior, and skull morphology. Galapagos sea lions are sexually dimorphic, with males growing larger than females and having several significant 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.

                                                          Adult males are robust in the neck, chest, and shoulders and are proportionately much smaller in the abdomen. As males mature sexually the enlarging sagittal crest becomes evident as a bump on the crown. The crest grows until the male reaches physically maturity, at which time it forms a prominent ridge above and behind the eyes, and creates a steep forehead. Galapagos sea lion males are said to lack the pale pelage coloration on top of the sagittal crest common in California sea lions, although this feature appears to be present in at least one published photograph. Also, the skull of adult male Galapagos sea lion has a 20-25% smaller sagittal crest, a shorter muzzle, is about 10% shorter overall and is narrower than the skull of male California sea lions. As in all otariids, the canine teeth of adult males are larger and thicker than those of females.

                                                          Adult and sub adult male Galapagos sea lion bark in often long repeated sequences. The bark is loud, rapidly repeated and distinctive. Females and juveniles do not produce the repetitive bark. Juveniles, sub adults and adults of both sexes will also growl. Adult females and juveniles do not have a sagittal crest. When viewed in profile, juveniles have a nearly flat head with little or no forehead. Adult females have a slight forehead formed by a gentle slope from the crown to the muzzle. In contrast to adult males, adult females have a long relatively thin neck and a wide torso.

                                                          Both sexes have a long and somewhat narrow muzzle that tapers to a slightly pointed nose. In profile, the face of younger animals is dog-like. The fore flippers have a sparse short fur that extends beyond the wrist onto the middle of the dorsal surface of the flipper in a “V” pattern and does not reach the round tip. The rest of the dorsal surface, and the palms of both fore flippers are covered with a hairless black leathery skin. The first digit is the longest, widest and thickest, and curves posteriorly, giving the flipper a swept back look. Digits 2-4 are successively shorter. There is a small opening in the skin at the end of each digit for a claw that is usually reduced to a vestigial nodule, and rarely emerges above the skin. The claw openings are set back from the free edge of the flippers by cartilaginous rods that extend the length of each digit, and expand the size of the flippers. The hind flippers also have cartilaginous rods that extend the length of each toe. The bones of the three central toes terminate at the position of the small nails that emerge through the skin on the dorsal surface, set back from the end of the flipper. The first and fifth toes are longer than the three middle toes, and the first toe, or hallux, is longer and wider than the fifth toe. The hind flippers have short hair covering part of the proximal end of the flipper, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin.

                                                          The color of Galapagos sea lion is highly variable. When dry, the coat of adult male’s ranges from greyish and golden brown to the common dark brown, and most bulls appear blackish or very dark when wet. Darkening begins when males are sub adults and in generally complete when a bull reaches physical maturity. Adult males can have light grey coloration on their backs. Adult females, juveniles and young sub adult males are pale colored above, and can be many shades of tan to light brown. There are often light colored areas on the muzzle, and around and above the eyes in both sexes. The sparse short fur covering a portion of the tops of the flippers can be the same color or darker than the color of the body. Pups are born with a longer brownish-black lanugo coat that fades to pale brown by three to five months. Pups go through their first molt at around five months and emerge with the pelage of adult females and juveniles.

                                                          There is little information on the lengths and weights attained by Galapagos sea lions, but they are said to be somewhat smaller than California sea lions. The dental formula is I 3/2, C 1/1, PC 6/5, but PC 5/5 occurs in approximately 25% of animals.

Dental Formula    I 3/2, C 1/1, PC 6/5, OR PC 5/5.

Size

Adult males are estimated to weight up to 250kg and grow up to 2.5m long. For adult females caring for pups weight from 50 to 100kg and 2m long. Pups of both sexes are born approximately six kilograms and weaned at approximately 25kg.

Life span

The age of maturity for Galapagos sea lions is about 4-5 years. Their life span is estimated to be 15- 24 years.

Gestation period    330 days. 

Can be confused with

Galapagos sea lions share the Archipelago with Galapagos fur seals. As vagrants, they may show up in the range of South American sea lions and South American fur seals, and there is a record of the former from the Galapagos.

Galapagos and South American fur seals have thick pelage and look shaggier, especially when wet, than Galapagos sea lions. Both fur seals are dark gray to brown and darker than similar-sized sea lions, with the exception of a fully-grown male Galapagos sea lion. Both fur seals have a more pointed muzzle and proportionately larger eyes and longer ears that stand out farther from the head when they are wet. Adults of both fur seals have long pale conspicuous vibrissae. Galapagos fur seals are the smallest otariids, reaching only 1.5 and 1.2 meters for males and females, respectively, and are stockier with a shorter neck and body than Galapagos sea lions.

South American sea lions have large blocky heads with a short, thick, blunt-ended muzzle. Adult male South American sea lions have huge fore quarters with a thick mane and a very large lower jaw.

Distribution

Galápagos sea lions can be found on all of the islands of the Galápagos archipelago. Less than a quarter of them reside on San Cristobal Island. They have also colonized Isla de la Plata, just offshore mainland Ecuador, 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 considered vagrant.

Ecology and behavior

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 of 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.

There are clear cut differences in behaviour between territorial 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 plays a key role in sexual selection and helps ward off intruding non-territorial males from a male's 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, along with 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", whereby territorial males decrease vocalization and aggression. Through repetitive encounters with other territorial bulls, males also store key information about a neighbor's strength as an adversary.

The average dominant bull holds his territory for only a few months. Because the dominant male of the harem cannot feed while defending his colony, he eventually becomes weakened and is overpowered by a well-nourished, fresh bull. On land, these fights start with two bulls stretching out their necks and barking to test each other's bravery. If this is not enough to scare the opponent off, they begin pushing each other and biting the opponent's neck. Males are equipped with thick, muscular necks that generally prevent lethal damage during these fights. Blood is often drawn, however, and many male sea lions bear battle scars from these territorial competitions. Losers are chased 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. Territorial males that lose their territory but decide to stay on the island tend to vocalize less.

Predation    The only predators they have are sharks, killer whales, and dogs.

Feeding and prey

Feeding mostly on sardines, Galápagos sea lions sometimes travel 10 to 15 kilometers from the coast over a span of days to hunt. This is when they come into contact with their main predators: sharks and killer whales. Injuries and scars from attacks are often visible. During El Niño events, occurring when the water temperature pattern changes in the Pacific, sardine populations either die or migrate, and sea lions dive deeper to feed on lantern fish. The reduction in food availability during El Niño leads to sea lion population declines. Successful pack hunting of yellow fin tuna, in which the fish were herded into a rocky inlet and occasionally onto land, was recorded in the BBC series Blue Planet.

Exploitation

Historically this sea lion was sporadically harvested for fat, meat and “trimmings” (vibrissae and testes). There was a government-sponsored cull in this century that was pursued with the hope of limiting population size and its impact on commercially important fish species. The chief suspected cause is the over-exploitation of stocks of Pollock in the high north pacific. Other reason suggested for the decline include long term change in ocean temperature, accumulation of human produced toxins and disease. It may be that the decline is attributable to the subtle interaction of several of these factors.

Threats and Status

the majority of the Galápagos population is protected, as the islands are a part of an Ecuadorian national park surrounded by a marine resources reserve. Although the Galápagos Islands are a popular tourist destination, strict rules exist to 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 as ocean temperatures warm and cold-adapted marine life on which the sea lions depend declines, which lead to die-offs or cessation of reproduction. Sharks and killer whales are the main predators of the sea lion. Although adult sea lions have less to worry about, pups are easy targets. Regulations governing human behavior help mitigate risks to sea lions due to human contact, but as the human population continues to grow it nevertheless presents risks of accident and disease. The sea lions have learned that being near the fisheries they have a better chance at capturing fish with little to no work, but as a result they are in more danger from boats and net entanglement. They are impacted by humans indirectly as well. Stray dogs introduced by humans form packs and attack sea lions. The pesticide DDT, still in targeted use to prevent malaria in tropical countries, accumulates through the food chain and is found at near-toxic concentrations in sea lion pups. From 2008 through 2012, death by disease increased. Galapagos Sea lions are known to be susceptible to canine distemper virus, however this disease is not believed to be endemic among the population.

Factors hypothesized include     

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

IUCN Status    Endangered (population decreasing)

Female With Pup