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). 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 Zalophus californianus (called Z. c. wollebaeki) by many authors. But genetic data supports Z. wollebaeki as a separate species. The species belongs to the family Otariidae and genus Zalophus.
Physical characteristics
Slightly smaller than their Californian congener, 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. Sexual dimorphism plays a small role in the physical characteristics and size of Galápagos sea lions, as males also tend to have a thicker, more robust neck, chest, and shoulders in comparison to their slender abdomen, whereas females 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. 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 pinnae of the external ears, which distinguish them from seals. The foreflippers have a short fur extending from the wrist to the middle of the dorsal fin surface, but other than that, the flippers are covered in black, leathery skin. Curving posteriorly, the first digit of the flipper is the largest, giving it a swept-back look. At the end of each digit is a claw, usually reduced to a vestigial nodule that rarely emerges above the skin. Although clumsy on land, sea lions are agile in water. With their streamlined bodies and flipper-like feet, they easily propel themselves through crashing surf and sharp coastal rocks. They also have the ability to control their flippers independently and thus change directions with ease. 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. The life span is estimated to be 15–24 years.
Distribution Galápagos sea lions can be found on all of the main islands of the Galápagos archipelago, and on a number of smaller islands in the area. 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.
Diet and feeding patterns
While information on the diet of Galapagos sea lions is limited, it is known that they are carnivores that feed mostly on sardines. They also eat other marine life like crustaceans, squid, fish (sardines and myctophids/lanternfish), and octopus, which classifies them as piscivores. Galápagos sea lions sometimes travel 10–15 km (6.2–9.3 mi) 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 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. A side effect of the close proximity that these sea lions choose to have with humans is the diversified array of food sources that the sea lions can choose from. In addition to the usual hunting strategies, sea lions have learned how to scavenge from fishing boats and have learned methods of hunting that involve the bright lights of the boats themselves.
Behavior and male competition
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