Sea lions and marine iguanas

Galapagos Islands Travel Blog

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Overnight the board left Santa Cruz and sailed to Rabida, a soothing rocking while we slept. Today was our day to play with Galapagos Sea Lions, an endemic subspecies of Californian sealion. The sealions covered the beaches, basking in the sun, sleeping and kissing. The adults ignored us completely even when we walked within a few feet of them. From close up we could watch the big males exert their dominance with loud grunts and spittle flying from between their sharp fangs.


The reason for the rich numbers of Galapagos Sea Lions on a few small islands on the equator comes from the Humboldt Current.

Named after Alexander von Humboldt, the Prussian naturalist who invented the contour map and first proposed that South America and Africa were once joined, it is responsible for the richness of the whole western South American coast. It is 160km wide and 3000km long. It moves at 3.7km/hour, bringing cold water from the Antarctic, forcing the upwelling of nutrient rich water through the warm but sterile surface. The current is deflected by the bulge of Peru out to the open ocean where it makes it to the Galapagos Islands before dying, providing the rich feeding grounds off the islands. All this changes during El Niño though, when the warm current from the equator displaces the Humboldt current, turning the water off the islands into a sterile desert with the rich water trapped deep below the surface.
This forces a collapse in the population of Sea Lions, penguins (lost 77% of their population) and marine iguanas, but an explosion in land iguanas, finches and mocking birds, as the El Nino brings more rainfall for the terrestrial species. Seabirds get a double hit - less fish in the ocean and huge number of mosquitoes on land, driving them away from their nests.

The Galapagos Sea Lions and Galapagos Tortoises show the two opposing evolutionary forces that act on the Galapagos Islands. Gigantism is common on islands, as a large body size allows easy gathering of food during rich times and storage during lean times, and predators are few. Yet Bergmann’s Law is the observation that closely related animals tend to be smaller towards the tropics, in order to be able to shed heat easier.

So we see animals like the Galapagos Tortoise and Flightless Cormorant, the largest of their types, and the reduced size of the Galapagos Sea Lion (compared the Californian Sea Lion), the Galapagos Fur Seal (the smallest marine mammal) and the Galapagos penguin (the second smallest penguin).


As well as the sea lions we saw baby Brown Pelicans being fed by their parents, sticking their beaks so far down their parents’ throats that we felt for sure they would be causing real damage. The adults weren’t thrilled about it either, they soon flew off again after being pestered by fledglings the same size as them. We saw American Oyster Catchers (which only became residents of the islands five years ago), hermit crabs, and Frigate Birds. We went for a walk inland into the arid part of the island and saw a solitary Galapagos Hawk sitting on a rock and came to a cove where Sally Lightfeet feasted on a dead pelican down on the rocks below.

I then snorkelled with marine iguanas and tropical fish, being surprised when sea lions sprang up in my face and darted away, while Lydia had to stay out of the water as her contact lenses were in her lost luggage.


We had a nap after lunch while the boat sailed to James Bay on Santiago. Here the Galapagos Sea Lion pups were feeling particularly frisky. Some spent the time suckling milk or sleeping, but the others wanted to play. Rather than being scared of us, we had to run back when they tried to climb over us or chase each other and us in a game. They came right up to us and investigated our snorkel gear, all the time making extraordinary noises and grunts. I snorkelled again, and this time saw a score of Pacific Green Turtles within a metre of me.


After snorkelling we walked to the other side of the island. On the rocky volcanic shelves we saw dozens of basking marine iguanas, lined up in rows to soak up the sun, in an effort to get warm enough to swim down into the water and collect algae. As the only marine lizards, iguanas are not adapted well enough to life in the water to be able to survive long periods in the ocean to gather algae. It is not breathing that is the problem – when Darwin found the marine iguana he tested its ability to hold its breath by weighting an iguana with an anchor and throwing it overboard attached to a rope. It was still alive when he hauled it up thirty minutes later. Their problem instead is holding enough heat in their body for them to use their muscles to swim back to shore.

The young iguanas are forced to take the slim pickings down at the water’s edge, and it is only the large males (who can grow to 1.3m long and 9kg) that can retain enough heat to swim down to 12m to eat the best algae fields. While marine iguanas have not solved the eat problem, they have adapted to the excess salt by concentrating it in small glands by the nose and constantly sneezing it out while sun baking, so standing next to the rows of marine iguanas we got splashed with small puffs of brine. Interestingly, marine iguanas and algae actually represent an inverted food pyramid, with the biomass of marine iguanas greater than that of the algae they eat, because the algae are able to grow so fast in the rich waters that the biomass added per unit of time is great enough to support the large population of marine iguanas. In order to survive the El Niño, when the sterile warm waters stop the algae from growing, the iguanas are able to resorb their bone mass and shrink by up to 20%.


Close by the marine iguanas were a few sea grottos where Galapagos Fur Seals hid in caves. The Galapagos Fur Seal is actually a sea lion that evolved from a parental species that lives on the southern tip of South America. Evolved to withstand great cold, it is in danger of overheating on the equator, so unlike the Galapagos Sea Lions which bask on the beach, it hides in sea caves during the day and hunts for fish at night.


That night we had many cocktails on board our boat, with a fun party in the Galapagos.


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Galapagos Islands
photo by: Melboorn