Galápagos sea lion
This article needs additional citations for verification. (July 2012) |
Galápagos sea lion | |
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Female | |
Male | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Clade: | Pinnipedia |
Family: | Otariidae |
Genus: | Zalophus |
Species: | Z. wollebaeki
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Binomial name | |
Zalophus wollebaeki Sivertsen, 1953
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Galápagos sea lion range |
The Galápagos sea lion (Zalophus wollebaeki) is a species of sea lion that lives and breeds on the Galápagos 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 through the surf. They are the smallest sea lion species.
Taxonomy
This species was first described by E. Sivertsen in 1953. It has been considered a subspecies of
Physical characteristics
Slightly smaller than their Californian relatives, Galápagos sea lions range from 1.5 to 2.5 m (4.9 to 8.2 ft) in length and weigh between 50 and 400 kg (110 and 880 lb), with the males averaging larger than females.[1][2][3] Adult males also tend to have a thicker, more robust neck, chest, and shoulders in comparison to their slender abdomen. Females, by contrast, have a longer, more slender neck and thick torso. The male's sagittal crest enlarges when he reaches sexual maturity, forming a small, characteristic bump-like projection on his forehead. Adult females and juveniles lack this trait and have a nearly flat head and little or no forehead. Galápagos sea lions, compared to California sea lions, have a slightly smaller sagittal crest and a shorter muzzle.[4]
Both male and female sea lions have a pointy, whiskered nose and long, narrow muzzle. Young pups are almost dog-like in profile. Another characteristic that defines the sea lion is the
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. Pups are born with a longer, brownish-black lanugo that 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 about 4–5 years.[1] The life span is estimated to be 15–24 years.[5]
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
Diet and feeding patterns
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:
Successful pack hunting of yellowfin tuna, in which the fish were herded into a rocky inlet and occasionally onto land, was recorded in the BBC series Blue Planet II.[9]
Behavior and male competition
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 behavior 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.
Breeding
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 begin developing their own hunting skills.
The lasting interaction of mother–offspring pairs is a central social unit in these sea lions.[10] 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 ensure a greater infant survival rate, but not Z. wollebaeki.[11] Plausible reasons for this low synchrony could be the absence of strong photoperiodic change throughout the year, which is thought to regulate embryonic diapause, and/or adaptation to an environment with variable productivity and prey availability.[11]
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.
References
Notes
- ^ . Retrieved 12 November 2021.
- ^ Galapagos sea lion - Galapagos Conservation Trust
- ^ Galapagos Sea Lion Facts | Galapagos Wildlife Guide
- PMID 17868473.
- ^ Reijnders et al. 1993
- ^ .
- ^ S2CID 84197080.
- S2CID 18977436.
- ^ "Blue Planet II - Filming Galapagos sea lions hunting tuna - BBC One". BBC.
- S2CID 23862471.
- ^ .
- S2CID 44050418.
- ^ Alava, Juan Jose; Salazar, Sandie; Cruz, Marilyn; Jimenez-Uzcategui, Gustavo; Villegas-Amtmann, Stella; Paez-Rosas, Diego; Costa, Daniel P.; Ross, Peter S.; Ikonomou, Michael G. (18 February 2011). "DDT Strikes Back: Galapagos Sea Lions Facing Increasing Health Risks". Royal Swedish Academy of Sciences: 1–3 – via AMBIO.
- ^ Denkinger, Judith; Guevara, Nataly; Ayala, Sofia; Murillo, Juan Carlos; Hirschfeld, Maximilian; Montero-Serra, Ignasi; Fietz, Katharina; Goldstein, Tracey; Ackermann, Mark; Barragan, Veronica; Cabrera, Francisco; Chavez, Cristina; Dubovi, Edward J.; Martinez, Jael; Trueba, Gabriel (1 July 2017). "PUP MORTALITY AND EVIDENCE FOR PATHOGEN EXPOSURE IN GALAPAGOS SEA LIONS (ZALOPHUS WOLLEBAEKI) ON SAN CRISTOBAL ISLAND, GALAPAGOS, ECUADOR". Journal of Wildlife Diseases: 491–498.
Further reading
- Kunc, Hansjoerg P.; Wolf, Jochen B. W. (2008). "Seasonal Changes Of Vocal Rates And Their Relation To Territorial Status In Male Galápagos Sea Lions ( Zalophus Wollebaeki)". Ethology. 114 (4): 381–388. .
- Meise, Kristine; Kruger, Oliver; Piedrahita, Paolo; Trillmich, Fritz (2013). "Site Fidelity of Male Galapagos Sea Lions: A Lifetime Perspective". Behavioral Ecology and Sociobiology. 67 (6): 1001–1011. S2CID 16971697.
- Wolf, Jochen B.; et al. (2005). "Males in the Shade: Habitat use and Sexual Segregation in the Galápagos Sea Lion (Zalophus Californianus Wollebaeki)". Behavioral Ecology and Sociobiology. 59 (2): 293–302. S2CID 25257905.
Other sources
- Zalophus wollebaeki: Galápagos sea lion, Ocean Biogeographic Information System(OBIS)
- Wolf, JB; Tautz, D; Trillmich, F (Sep 2007), "Galápagos and Californian sea lions are separate species: Genetic analysis of the genus Zalophus and its implications for conservation management", Frontiers in Zoology, 4 (1): 20, PMID 17868473
External links
- Galápagos sea lions and fur seals
- Photos of Galápagos sea lion on Sealife Collection