The Galapagos sea lion (Zalophus wollebaeki) lives on all large and small islands and rocks in the Galapagos Islands, and sometimes can be found on Isla de la Plata near mainland Ecuador. They are the smallest of all sea lion species. The Galapagos sea lion was considered a subspecies of the California sea lion. Recent evidence is in support of them as a full species.
Adult Galapagos sea lion males tend to have a thicker, more robust neck, chest, and shoulders in comparison to their slender abdomen. Females have a longer, more slender neck and thick torso in comparison. In size, the species can be from 4.9 to 8.2 ft in length and weigh between 110 to 880 lb, with the males on average larger than females.
Sea lions are a shade of dark brown when wet, but once dried, their colour varies greatly. The females tend to be a lighter shade than the males and the pups are a chestnut brown.
Feeding Behaviour
In the Galapagos, sea lions eat fish mostly sardines, in surface and coastal upwelling water, but will also feed in deep water, and in water over muddy and sandy bottoms along the continental shelf or both in shallow and deep waters between rocks.
During El Niño years, 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.
Galapagos Sea Lion Breeding Behaviour
Galapagos sea lions breed from May to January. After about a week, the pups go to sea with their mothers to catch fish and periodically come ashore to nurse. Pups are weaned after about a year but some continue to nurse for up to two years.
Females enter estrous a few weeks after giving birth and prepare to mate. Adult females and pups are very tame toward humans often ignoring their presence.
Many mammals synchronize their pregnancies to ensure a greater infant survival rate. Not Z. wollebaeki.
Possible explanations 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.
Survival Threats
The majority of the Galápagos population is protected since 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.
There are about 30,000 Galapagos sea lions – the population varies year to year and can be between 20,000 and 50,000 sea lions. Some threats do exist. el Niño events can lead to die-offs or cessation of reproduction ocean temperatures warm and cold-adapted marine life on which the sea lions depend decline.
Additionally, pups are easy prey for sharks and killer whales. Sea lions have learned that being near our fishing zones they get a better chance at capturing fish with little work, but they are in more danger there from boats and net entanglement.
References:
- Dasmahapatra, KK, J I Hoffman and W Amos. 2009. Pinniped phylogenetic relationships inferred using AFLP markers. Heredity 103: 168–177.
- Dellinger, T. and F. Trillmich 1999. Fish prey of the sympatric Galápagos fur seals and sea lions: seasonal variation and niche separation. Canadian Journal of Zoology 77: 1204-1216
- Rice DW 1998. Marine Mammals of the World: Systematics and Distribution. Society for Marine Mammalogy, Lawrence, KS.
- Trillmich, F. and Limberger, D. 1985. Drastic effects of El Niño on Galapagos pinnipeds. Oecologia 67: 19-22.
- Wilson, D. and S. Ruff. 1999. Smithsonian book of North American mammals. UBC Press, Vancouver.
- Wolf, JBW, D. Tautz and F. Trillmich. 2007. Galápagos and Californian sea lions are separate species: Genetic analysis of the genus Zalophus and its implications for conservation management. Frontiers in Zoology 4:20
- Villegas-Amtmann, S., DP Costa, Y Tremblay, S Salazar, and D Aurioles-Gamboa. 2008. Multiple foraging strategies in a marine apex predator, the Galapagos sea lion Zalophus wollebaeki. Marine Ecology Series 363: 299–309.