The Galapagos Islands, a volcanic archipelago positioned directly west of Ecuador, are renowned for their unique and diverse wildlife. Among the most charismatic inhabitants of this natural paradise is the Galapagos sea lion ( Zalophus wollebaeki). These playful and inquisitive marine mammals are a common sight throughout the islands, captivating visitors with their charming antics and intriguing behaviors. This article delves into the world of the Galapagos sea lion, exploring its diet, habitat, physical characteristics, social behavior, and the challenges it faces in a changing environment.
Endemic Species and Unique Flora
The Galapagos Islands are home to some of the highest levels of endemism anywhere on the planet. About 80% of the land birds, 97% of the reptiles and land mammals, and more than 30% of the plants are endemic. More than 20% of the marine species in Galapagos are found nowhere else on earth. Favorites include the giant Galapagos tortoise, marine iguana, flightless cormorant, and the Galapagos penguin - the only penguin species to be found in the Northern Hemisphere.
Many visitors to Galapagos are surprised to be greeted by desert-like vegetation-most are expecting a continuation of the lush greenery they witnessed on mainland Ecuador. In fact, the majority of the archipelago’s land area is covered by the brown and grey vegetation often found in deserts. The Galapagos Islands are situated in the Pacific Dry Belt, and in average years only the highest altitudes of the larger islands receive enough rainfall to support tropical plant life.
Geologically speaking, the islands are young, and much of the island’s plant life reflects this; many species seem to be in the midst of the evolutionary process, which makes classifying them a difficult task. To date, the Islands are believed to be home to more than 600 native species of vascular plants and approximately 825 introduced species, the majority introduced by humans. More than 100 of the introduced species have become established in the wild, with many of them extremely invasive and of major concern. Three introduced plant species have been eradicated. Mainland Ecuador, on the other hand, has about 20,000 species. The discrepancy between species number on the Islands and the mainland highlights the fact that the Galapagos Islands are separated from the continent by a hostile saltwater barrier reducing the potential for arrival and, once a plant has arrived, establishment is difficult due to the harsh environment. It is worthy of note that more than 30% of native plant species found in Galapagos are endemic (not found anywhere else on earth). The flora of Galapagos can be grouped into three major vegetation zones: the coastal zone, the arid zone, and the humid highlands. Coastal plants are found in the narrow zone near the shore and are distinctive because of their tolerance to salty conditions. Mangrove trees are one of the most common plants found in this zone, and they serve an important role as the breeding sites for many birds, such as pelicans and frigatebirds. They also provide much needed shade regions for iguanas and sea lions, as well as refuges for sea turtles. The dry area is the most extensive zone in Galapagos and is comprised of plant species that are highly adapted to drought-like conditions, such as succulent cacti and leafless shrubs that flower and grow leaves only in the brief rainy season. Located above the dry zones are the very lush and green, humid zones. In portions of this zone, Scalesia trees form a very dense forest in the humid zone, with their branches adorned with mosses, liverworts, and epiphytes - non-parasitic plants that use larger trees only for support. The humid zone is only found on the larger, higher islands.
Distribution and Habitat
Galapagos 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. They occupy many different shoreline types, from steep, rocky cliff sides to low-lying sandy beaches.
Read also: Galapagos Hawk Feeding Habits
Physical Characteristics and Sexual Dimorphism
Galapagos sea lions are sexually dimorphic, with males larger than females. 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. Adult 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. 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. 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.
Diet and Foraging Behavior
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. They are outstanding divers, able to get to significant depths to find their prey, and to stay there for up to 10 minutes. 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.
Social Behavior and Reproduction
Galápagos sea lions are very social and on land, they form colonies in their hauling-out areas. As males grow larger, they fight to win dominance of a harem of between five and 25 cows, along with the surrounding territory. Swimming from border to border of his colony, the dominant bull jealously defends his coastline against all other adult males. The average dominant bull holds his territory for only a few months. Because the dominant male of the harem cannot feed while defending his colony, he eventually becomes weakened and is overpowered by a well-nourished, fresh bull.
Breeding takes place from May through January. Each cow in the harem has a single pup born a year after conception. After about a week of continuous attention from birth, the female returns to the ocean and begins to forage, and just a week after that, the pup will follow her and begin to develop its swimming skills. When the pup is two to three weeks old, the cow will mate again. The mothers will take the young pups with them into the water while nursing until around the 11th month.
Read also: Facts About Galapagos Penguins
Galapagos sea lions are quite vocal. Adult males often bark in long, loud and distinctive repeated sequences. Females and juveniles do not produce this repetitive bark, but both sexes of younger pups will growl. Vocalization plays a key role in sexual selection and helps ward off intruding non-territorial males from a male's harem.
Interactions with Other Species
Galapagos sea lions are known to have special friendship with Lava lizards on Barrington Island. The lava lizards are often found resting on or around Galapagos sea lions. Some finch species have developed a mutualistic relationship with giant tortoises, feeding on the ticks that hide in the folds of the tortoise’s reptilian skin or on their shell.
Threats and Conservation Status
The Galapagos sea lion is listed by the IUCN red list as Endangered with decreasing population trend. The biggest threat to the Galapagos Sea Lion is the El Niño weather phenomenon. El niño occurs every decade or so, affecting the whole coastline of South America. El niño causes a small rise in sea temperatures, which in turn reduces nutrient levels found in the ocean. Fewer algae, plankton, and nutrients mean fewer fish, which also means hungry sea lions. Lack of food disrupts Galapagos sea lion breeding and causes a high infant pup mortality rate. It can take many years for a Galapagos sea lion population to recover after an el niño event.
Human behavior is also a risk to the Galapagos sea lion. Plastic waste in the ocean is easily mistaken for squid and often kills sea lions if ingested. Sea lions can also become caught in fishing nets, as was the case for one Galapagos sea lion named Panchita. Poor Panchita was rescued but suffered severe cuts to her body.
The majority of the Galápagos population is protected, as the islands are a part of an Ecuadorian national park surrounded by a marine resources reserve. Although the Galápagos Islands are a popular tourist destination, strict rules exist to protect all wildlife from disturbance.
Read also: Galapagos Shark Habitat
Galapagos Sea Lions and Tourism
With its fun and inquisitive nature and at times, comical behavior, the Galapagos sea lion is often a creature that brings much amusement and joy to visitors to the Galapagos Islands. A special highlight for those that experience it is swimming and snorkeling among the sea lions. These nimble creatures will swim seemingly right up to a snorkeler’s face before darting away at the last minute and they love to play with people in the water in this way.
Visitors don't need to be shy about taking photos or approaching sea lions at Galapagos, but please remember to maintain a minimum distance of 2 meters (6 feet). You must also never touch a Galapagos sea lion.