The pinnipeds (flippered feet) comprise 33 species around the world, divided
into three groups: true seals (Phocidae), eared seals (Otaridae) and walruses
(Odobenidae). Galápagos has two species, both eared seals: the endernie Galápagos fur
seal (Arctocephalus galapagoensis), and the endemic subspecies of the Californian
sea-lion, the Galápagos sea-lion (Zalophus californianus wollebacki). Galápagos
therefore has no 'true' seals.
The cared seals are characterised by external ear pinnae, by the ability to rotate their
hind flipper under their pelvic girdle and by their long, flipper-like front limbs. True
seals have heavy claws on their front limbs which are very hand-like. Unlike cared seals,
true seals must shuffle along on their pelvic girdles like huge maggots, with their hind
flippers always trailing. Eared seals on the other hand can gallop - even out-running a
person on rocky terrain! When swimming, cared seals use their fore flippers simultaneously
for propulsion and their hind flippers as rudders, while true seals use their fore
flippers as rudders, and their hind flippers in an alternate sculling motion. Usually
associated with cold environments, the two Galápagos seals have the most tropical
distribution of any pinnipeds in the world. Probably the strongest memory of any visitor
to the islands is the delight felt when swimming and interacting with these two
intelligent mammals.
GALAPAGOS SEA-LION (Zalophus californianus wollebacki)
There is a large degree of sexual dirnorphism (differences between the sexes apart from
genitalia) in sea-lions. Males weigh up to 25Okg while females reach only 1OOkg. There are
approximately 50,000 individuals, well dispersed around the archipelago. Sea-lions like to
haul out on sandy beaches. The best places to see them are probably Plaza Sur, Isla
Mosquera, Gardner Bay on Espaflola, Rábida and Puerto Egas on Santiago.
Males establish territories which are savagely defended from rivals and
interlopers, forcing the unsuccessful bulls to leave the area and set up bachelor colonies
away from the female haul-outs. Reproduction occurs mostly in the garúa season (July to
December) although this varies from island to island. Three to four weeks after pupping,
the female comes back into oestrus and the bull copulates with her. As in the fur seal,
there is a system of delayed implantation, whereby the fertilised egg floats in the uterus
for approximately two months before implanting. After the single pup is born (rarely
twins) the mother stays with it for the first week and completes the pair bond, both by
vocalisation and by smell. Then she begins to forage by day, returning to suckle in the
evenings. At five weeks old, the pups moult their baby coat or lanugo, to look more like
miniature adults. By about five months old pup will begin feeding inshore for itself hut
may be dependent on its mother a lot longer.
Bulls are polygamous and make little or no parental investment. They do not maintain a
true harem, simply defend an area of beach. The dominant bull has the territory most
favoured by the females, so (like the marine iguanas) is able to mate with more females
than a less dominant bull.
Sea-lions are highly thigmotactic (they seek body contact) and loaf around in piles on the
beach. They are extremely efficient hunters, preferring sardines to other fish, so spend a
considerable time resting or at play. Underwater they 'are extremely weli streamlined,
lithe and acrobatic. Only the bulls should be avoided - they are easily recognised, not
only by their large size, but by the pronounced bump on their forehead. The young are
highly inquisitive and it is not unusual for them to nibble on a snorkeller's flippers
while swimming. Serious injuries can be inflicted by the bulls, and they should be given
the distance and respect they seek.
Text: Galápagos Wildlife a visitor's guide.
