EARED SEALS

Galapagos Sea Lion (Zalophus wollebaeki)

Galapagos Sea Lions (Zalophus wollebaeki) are native to the Galápagos Islands, also occasionally being spotted off the Ecuadorian and southern Colombian coasts. Their latin name ‘zalophus’ comes from the appearance of the sagittal crest on the head of the males, with ‘wollebaeki’ deriving from Norwegian zoologist Alf Wolleback who conducted an expedition to the Galápagos in 1925. The species is Endangered. Estimated population size = 15,900.
Z. wollebaeki are the smallest species amongst the sea lions (males up to 2.4 m long/ 250 kg, females up to 1.8 m/ 95 kg), slightly smaller in stature than their closely related Californian cousins (Zalophus californianus). Sexual dimorphism is still apparent with males considerably larger, though maybe to a slightly lesser extent than in other species. The males have strongly built bodies with robust shoulders, necks and chests, and smallish heads with pointy, whiskery muzzles. Characteristically, they have the raised bumps or sagittal crests on the tops of their heads from maturity. Females are much more slender, also with small heads and narrow, dog-like muzzles. Flippers in both are black and leathery from the wrists, and otherwise covered in fur. Both sets are broad and proportionally short compared with other species, though streamlined as in all otariids. Colouration of Z. wollebaeki is dark brown to tan, to pale and sandy, varying greatly and depending on whether the coat is wet or dry. The undersides are often lighter and may even appear yellowish, and the male sagittal crest may be highlighted too.
Feeding behaviour:
A popular prey of Z. wollebaeki is sardines, but they will also eat lanternfish, green-eyes, squid and deep-sea smelt during times of reduced availability, owing to their propensity to dive deep (up to 584 metres). They may forage offshore for days at a time, and sometimes cooperatively hunt larger prey such as tuna, though females tend to favour shallower shelf areas.
Breeding behaviour:
Sexual maturity – males 4-5 years old/ females 4-5 years old.
Males stake out shoreline territories in this polygynous species, which they will later vigorously defend. Copulation with multiple mates occurs in the shallow water during a protracted breeding season which lasts from May right through to January, and gestation duration is approximately 11 months. Unlike many other pinnipeds, female Z. wollebaeki do not synchronise their births with each other, and as a result this affords them little protection in the form of safety in numbers. Possibly as a result of the continuous climate so close to the equator, this means there are pups nursing almost all year round. For the first week, the mothers remain with their brown/black pups constantly, before beginning routine foraging trips lasting several days and incrementing. Lactation occurs for at least a year, but it is not uncommon for it to last 2 or more, even overlapping with the birth of the next pup. The lanugo is shed at around 5-6 months of age, although it will become paler over time, and the pup will be comfortable in water from just 1 or 2 weeks old. The pups group together in the rookeries while awaiting the return of their mothers, who often arrive back at night time. Moulting is thought to occur after breeding. The average longevity for Z. wollebaeki is around 15-24 years.
Since being granted separate species status from the California Sea Lion, the species has no subdivisions.

Photos: (1, 2) Kayleigh Jones (3) Katharina Peters

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