Galapagos Sea Lion
Names: The Galapagos Sea Lion, or “Pagos Sea Lion,” is now considered by most sources a separate species, Zalophus wollebaeki, from the closely related California Sea Lion, Zalophus californicus. In 2003 it was raised from subspecies Zalophus californicus wollebaeki to a separate species, based on behavioral differences (see IUCN Red List reference). All sea lions are in the Phylum Chordata, Class Mammalia, Order Carnivora and Family Otariidae. The other sea lion that is most closely related to Z. californicus and Z. wollebaeki is the Japanese Sea Lion, Z. japonicus, which is believed to be extinct (1950s). The Galapagos Sea Lion literally translates to “León Marino de Galápagos,” but it is frequently called “Lobo de Mar” (sea wolf).
Description: Family Otariidae seals are also known as “Eared Seals,” distinguished by small, but visible ears. They also have front flippers they “walk on” and use for swimming. True seals, family Phosidae, have only ear holes, and cannot support themselves on their front flippers. The Galapagos Sea Lion is very similar in appearance to the California Sea Lion, but smaller. Males can reach 250kg at maturity, and develop a thicker neck, and longer and thicker canines, than the females. The males also develop a large ridge behind the eyes that gives it its distinctive steeper forehead. Both sexes are dark brown when wet and creamier brown when dry, although individuals can range from gray to reddish to almost black. Adult females tend to be lighter in color than adult males. Pups have longer, thicker fur, which they molt at around 3 - 5 months. The Galapagos Sea Lions are distinguished from the Galapagos Fur Seals by their larger size, longer necks, and thinner, less shaggy coat. Sea lions also have a longer snout.
Distribution: The Galapagos Sea Lion is endemic to the Galapagos Islands, and can be found on most of the islands. Obis SeaMap reports a colony on Isla de la Plata, 17 miles off the coast of Ecuador, and a record of one from Isla del Coco, ~500km from Costa Rica.
Habitat: Galapagos Sea Lions can be found “hauled out” of the water on a variety of rocks, ledges and beaches throughout the archipelago. “Harems”, or colonies, are usually found on sandy or rocky, gently sloping beaches. The term harem refers to a stretch of beach dominated by a single male, also known as the “beach master”. Harems can have just a few or up to 30 females and their pups. Females seem to be free to move from one “harem” to another, but no other males may approach without being challenged by the beach master!
Abundance and Density: The population of Galapagos Sea Lions has fluctuated hugely from an estimated 50,000 in 1979, down to only 14,000–15,000 in 2001. Warmer water temperatures during El Nino events cause a dramatic decline in the sea lions’ food supply. Not only do large numbers die during these events, but the sea lions also cease to reproduce. In addition, a virus called “Sea Lion Pox”, believed to be transmitted by mosquitoes, has recently been affecting some colonies. The sea lion pups are also affected by an eye parasite, Philophthalmus zalophi.
Diet: It is believed that Galapagos Sea Lions live mainly on fish and squid. Nursing females tend to feed their pups at night and go to open water to feed (for up to 12 hours) during the day, after the first 6- 7 days after birth. (This feeding strategy is the reverse of the Galapagos Fur Seals, which nurse during the day and feed at night.) The pups are left as a group, with one female to watch over them. The beach master will also chase any pups that wander too far off shore back on to the beach to keep them safe from sharks, while he patrols his territory.
The graph above compares diet samples of Galapagos Fur Seal and Galapagos Sea Lions collected during typical (1984, 1985, 1986) and El Nino (1983) years.
Reproductive Ecology: While we’re there, there should be a lot of action in the sea lion colonies. The beach masters should be on patrol, since breeding and pupping occur from May through January. These males defend their stretch of beach so vociferously and continuously, without feeding, that they usually can only hang on to a harem for ten days to three months. Then they retire to a “bachelor colony” to regain their strength. The gestation period is nine months, but sea lions keep their pupping on an annual cycle by “delayed implantation”, where the fertilized cell doesn’t continue to divide, or become implanted, for two months.
Human Impact: The Galapagos Sea Lion is one of the species we think of when we think Galapagos. They are world renowned for their curiosity, their playfulness and their beauty. Unfortunately, humans are having a negative impact on them in a variety of ways. One of the Charles Darwin Foundation’s current “Featured Projects” is “Sea Lion Monitoring and Conservation”. They described a variety of problems related to the increasing human activity on and around the islands by tourists and large- scale fishing. These include: Fishing related waste, such as hooks, long lines and nets; fisheries by– catch, particularly of the very curious young pups; and increased tourist presence at their nursery sites. The project will include monitoring the current population, recording the number of hooked or entangled animals, and setting up a system for rescuing injured animals (see website below).
Charles Darwin Foundation. Sea Lion Monitoring and Conservation. 20 June 2007. http://www.darwinfoundation.org/en/our-work/featured-projects/sealion-monitoring
Charles Darwin Foundation. Galapagos Sea Lions. Charles Darwin Research Station Fact Sheet. 20 June 2007. http://www.darwinfoundation.org/files/species/pdf/sea-lion-en.pdf
Fitter, Julian, Daniel Fitter, and David Hosking. 2000. Wildlife of the Galapagos. Princeton: Princeton Univ. Press.
Jackson, Michael H. 1993. Galapagos: A Natural History. Calgary: Univ. Calgary Press.
OBIS-SEAMAP: Read, A.J., Halpin, P.N., Crowder, L.B., Best, B.D., Fujioka, E.(Editors). 2007. OBIS-SEAMAP: Zalophus wollebaeki (Pagos Sea Lion). World Wide Web electronic publication. http://seamap.env.duke.edu/species/tsn/622014, Accessed on June 20, 2007.
Seal Specialist Group 1996. Zalophus wollebaeki. In: IUCN 2006. 2006 IUCN Red List of Threatened Species.
Trillmich, F., AND T. Dellinger. 1991. The effects of El Niño on Galapagos pinnipeds. Pp. 66-74 in F. Trillmich, and K. A. Ono, eds. Pinnipeds and El Niño: Responses to environmental stress. Ecological Studies 88. Springer-Verlag, Berlin.