EARED SEALS

California Sea Lion (Zalophus californianus)

The California Sea Lion (Zalophus californianus), native to California and found along the western coast of the USA as far north as southern Alaska and as far south as central Mexico, is an eared pinniped, or otariid, of the sea lion variety. Its genus name, Zalophus, translates as ‘intensive crest’, which refers to the protruding ridge of bone that runs through the midline of the sea lion’s skull, called the sagittal crest. Z. californianus is identified as a Least Concern species. Estimated population size = 387,646.
Sea lions in general are larger than fur seals, but Z. californianus is one of the smaller sea lions (males up to 2.5 m long/ 500 kg, females up to 1.8 m/ 110 kg). Eared seals are all sexually dimorphic though, with males larger than females. Eared seals typically have long, slender fore flippers, developed chest muscles, and distinctively, the ability to turn their hind flippers forward and walk on all fours. This allows them to move at speeds on land, unlike the slow ‘humping’ gait that the true seals are restricted to. The sea lion’s body appears more shiny than that of the fur seals, with only coarse guard hairs protecting the short hairs of the coat. The California Sea Lion is no exception to these characteristics. With a pointy muzzle, large eyes, sharp canines, and thick, abundant whiskers, or vibrissae, Z. californianus has a distinctly dog-like appearance. The head of the female is quite small and compact, whilst the head of the male has the sagittal crest which gives him a crown-like protrusion on the head, often a lighter colour than the rest of the body. Males are also notably more stocky and strongly-built than the females. Colouration varies from dark brown or black in males, to tan or even sandy in females, but can appear vastly darker when wet. Finally, adult males have a thick neck and mane, which also separates them from the females.
Feeding behaviour:
Feeding preferences of Z. californianus vary enormously with population location and seasonal prey abundance, but the diet generally consists of several favoured oceanic fish and cephalopods. These can include a variety of: sardines, anchovies, hake, herring, mackerel, rockfish, octopus, squid, salmon, lamprey, toadfish, dogfish and bass. They have been known to hunt in cooperation with other marine animals in pursuing large schools of fish.
Breeding behaviour:
Sexual maturity – males 4-5 years old/ females 4-5 years old.
Z. californianus are polygynous breeders, with territorial males mating with multiple females in water or at the water’s edge. Gestation is 9 months, with, as is common in pinnipeds, a 3 month delayed implantation period. The females haul out around May, selecting their location based on their choice of male, and pups begin to be born from mid-June, through to mid-July. A mother will remain with her offspring for around 7-10 days at first, before returning to the sea to feed for days at a time. She will then start a cycle of foraging at sea and returning to nurse, and continue this for approximately 11 months until the pup is weaned. This period is flexible and can be shorter, or can even continue for a couple of years! Pups are born with a dark brown/blackish coat that is moulted within the first few months, and the replacement, paler brown, coat itself will also be moulted another 4 or 5 months later, as development continues. The young are very soon capable of accompanying their mother on local foraging trips. Moult for these animals is autumn through to winter (females first, males later). The final difference at the conclusion of breeding season is that while females go off to forage nearby, males often migrate north to feed. The usual maximum lifespan for Z. californianus is around 25 years.
The extant Galapagos Sea Lion and the extinct Japanese Sea Lion were once considered subspecies of Z. californianus, however evidence has since proved that they are in fact, separate species of their own.

Photos: Michael H Smith (top) and Martin Stoffel

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