Zalophus wollebaeki, Sivertsen, 1953
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https://doi.org/ 10.5281/zenodo.6604474 |
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DOI |
https://doi.org/10.5281/zenodo.6606872 |
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persistent identifier |
https://treatment.plazi.org/id/965C87FE-1E52-5641-9C1A-94828849F429 |
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treatment provided by |
Diego |
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scientific name |
Zalophus wollebaeki |
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Galapagos Sea Lion
Zalophus wollebaeki View in CoL
French: Otarie de Wollebaek / German: Galapagos-Seelowe / Spanish: Leén marino de las Galapagos
Other common names: Galapagos Sealion
Taxonomy. Zalophus wollebaeki Sivertsen, 1953, View in CoL
“Floreana, (Sancta Maria), Galapagos Islands,” Ecuador
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Formerly referred to as Z. califormianus wollebaeki , one of three subspecies of Z. californianus . The closely related Z. californianus , Z. wollebaeki , and the extinct Z. japonicus are now full species. Monotypic
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Distribution. Galapagos Is in the equatorial Pacific Ocean, including all main islands and numerous smaller rocks; irregularly on Isla de la Plata off mainland Ecuador. View Figure
Descriptive notes. Total length c.150 cm (males) and 120 cm (females); weight up to 250 kg (males) and 50-100 kg (females). Newborns are 60-80 cm (average 73 cm) and c.6 kg. Dental formula varies: 75% of individuals with 13/2, C 1/1, PC 6/5 (x 2) = 36 and 25% with 1 3/2, C 1/1, PC 5/5 (x 2) = 34. Galapagos Sea Lions are superficially similar to California Sea Lions ( Z. californianus ), but they are smaller and exhibit several other differences, including lesser degree of sexual dimorphism. Nevertheless, male Galapagos Sea Lions are often double the weight of females. Mature males have well-developed upper torsos and necks, but their skulls are shorter, with smaller sagittal crest. Crest grows tall enough to produce noticeable forehead rise. Because they lack sagittal crest, female Galapagos Sea Lions have a flatter head silhouette, showing only slight forehead, and they have a more gracile neck. Muzzles in both sexes are relatively narrow, tapering to nose, and faces ofjuveniles can have a canine appearance. Foreflippers have some hair on dorsal surfaces, but hair does not extend to rounded tips. Otherwise, flippers, including undersides, are covered with dark leathery skin. First digit is the longest and curves back. Cartilaginous rods in hindflippers lengthen toes, and first and fifth digits are longer than three middle digits. Similar to foreflippers, hindflippers have hair on upper parts closest to body, but otherwise are covered in dark leathery skin. Coat color in adult male Galapagos Sea Lions darkens as they age and can vary from typical dark brown to grayish or golden brown, and pale areas can occur on the muzzle and around the eyes. When wet, coat appears almost black. Adult females and juveniles are usually some shade of buff to pale brown. Newborns have blackish coat that lightens to brown within 3-5 months, followed by a molt into the female/juvenile pelage.
Habitat. Sandy and rocky shores of volcanic islands of the Galapagos Archipelago and coastal islands as haul-out sites. Favored locations for breeding rookeries of the Galapagos Sea Lions are sandy or rock-strewn beaches. Terrestrial predators in this habitat were essentially nonexistent until settlers brought dogs to the islands, and they have killed young. Killer Whales (Orcinus orca) are potential marine predators, and sharks attack Galapagos Sea Lions, many of which have bite scars. Near rookeries, Galapagos Sea Lions have been seen to drive off Galapagos sharks (Carcharhinus galapagoensis ) that approach too closely.
Food and Feeding. Feeding habits of Galapagos Sea Lions are not well studied, but they eat sardines ( Clupeidae ), lanternfish ( Myctophidae ), deep-sea smelts ( Bathylagidae ), and squid. During El Nino weather patterns when food resources are scarce, greeneye fish (Chlorophtalmidae) are added to the diet. Galapagos Sea Lions will thrash octopuses at the water’s surface, presumably before eating them. Lactating females feed both day and night, in contrast to nocturnally feeding Galapagos Fur Seals ( Arctocephalus galapagoensus ).
Breeding. The Galapagos Sea Lion has the same general polygynous breeding system as described for the New Zealand Sea Lion ( Phocarctos hookeri ). For Galapagos Sea Lions, breeding takes place in May—January. Males maintain territories for 10-60 days on land or in shallow waters, where most of the copulations occur. After a gestation of c.11 months, a female bears a single offspring annually. She nurses her young for 4-7 days and then leaves for a series of foraging trips that last 0-5-3 days during the cool season. During the warm season, trips may last longer. Some females return at night to nurse their offspring and leave again at dawn. When they are only 1-2 weeks old, young enter shallow waters to learn how to swim. They may be weaned at 11-12 months old (weighing 25-40 kg), but most continue to nurse into their second year. Because the Galapagos Sea Lion is non-migratory, breeding season is long, and females often care for their young for more than a year; nursing offspring can be found on rookeries throughout the year. A female may continue to care for a yearling after she gives birth, or she may skip the annual birth cycle (or spontaneously abort) if she is already attending an older offspring. Age of maturity for both sexes is c.4-5 years. Life span is c.15-24 years.
Activity patterns. At sea, Galapagos Sea Lions may rest at the water’s surface, rafting in groups, with one or more flippers held in the air. On land during the breeding season, female Galapagos Sea Lions thermoregulate by using shade from ledges, cliffs, and vegetation when available, or they cool off in wet sand, tidal pools, or the ocean during heat of the equatorial day. Dive depths of lactating females are 45-150 m, lasting 3-5 minutes. Deepest record dive was to 338 m, and longest dives lasted 9-8 minutes.
Movements, Home range and Social organization. The Galapagos Sea Lion is nonmigratory and remain at the Galapagos Islands throughout the year. An island near the mainland coast of Ecuador, Isla de la Plata, became the site of a breeding rookery in 1986, butit is only been used irregularly. Sea lions have been seen in Costa Rica, including Isla del Coco, but these could be California or Galapagos Sea Lions. Vagrant Galapagos Sea Lions have also been seen at Isla Gorgona, Colombia.
Status and Conservation. Classified as Endangered on The IUCN Red List. Current total population of the Galapagos Sea Lion is ¢.20,000 individuals, one-half of whatit was in 1978. Size of the population oscillates between 20,000 and 40,000 individuals, depending on marine productivity, which may dramatically decrease during El Nino events leading to mass mortality and interruption of the breeding cycle. The Galapagos Sea Lion enjoys legal protection by the Ecuadorian government, which manages the Galapagos Islands as a national park and restricts commercial fishing operations in the area. Feral dogs occasionally kill Galapagos Sea Lions and, potentially, could transmit canine diseases, especially where there is frequent contact near settled areas. Outbreaks of sea lion poxvirus have occurred during past El Nino events, when Galapagos Sea Lions were already stressed by reduced availability of food.
Bibliography. Alava & Salazar (2006), Aurioles & Trillmich (2008f), Dellinger & Trillmich (1999), Heath & Perrin (2009), Jefferson et al. (2008), Jeglinski et al. (2012), Kooyman & Trillmich (1986), Mueller et al. (2011), Odell (1981), Orr (1967), Reijnders et al. (1993), Rice (1998), Schramm et al. (2009), Trillmich (1979, 1986b, 1990), Trillmich & Dellinger (1991), Trillmich & Trillmich (1984), Trillmich & Wolf (2008), Villegas-Amtmann et al. (2008), Wolf et al. (2007).
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