The Galapagos penguin (Spheniscus mendiculus) is the only penguin species that lives and forages north of the equator. Its survival depends on the unusual confluence of cold-water currents, primarily the Humboldt and Cromwell currents, which create a temperate marine environment in this tropical setting. This mixing zone causes the upwelling of nutrient-rich waters that sustain its prey base. Classified as endangered, the species is highly vulnerable to the unpredictable nature of its food supply.
Primary Species Consumed
The diet of the Galapagos penguin is highly specialized, consisting almost entirely of small, schooling fish that inhabit the cool, coastal waters. These opportunistic carnivores rely on the abundance of species like Pacific sardines (Sardinops sagax), anchovies, and mullet. These prey items are generally small, typically measuring no more than 15 millimeters in length, allowing the penguins to consume them quickly underwater.
These specific fish species form the bulk of the diet because they depend on the nutrient-rich conditions created by the cold currents. The fish are drawn to areas of strongest upwelling, which correlates directly with where the penguins concentrate their foraging. Availability of these cold-water species is the most important factor determining whether a penguin can successfully feed, molt, or breed. Due to their small body size, they require a consistent, high-density food source to maintain their metabolism in the warm climate.
While the diet is focused on these schooling fish, the exact composition can fluctuate seasonally based on the strength of the currents. During periods when upwelling is less intense, the penguins may also consume small crustaceans or other marine invertebrates. These are generally considered secondary or supplementary food sources that become more important only when the preferred, energy-dense fish are scarce. The reliance on schooling fish means that when these populations decline, the penguins lack a readily available alternative to sustain themselves.
Unique Foraging Methods
Galapagos penguins employ a specific pursuit hunting strategy to capture their mobile, schooling prey in the water column. They are visual predators, using their agility underwater to chase and seize individual fish from within a school. Observations show that they often approach prey from below, a technique that leverages their counter-shading camouflage against the lighter surface water.
Their diving behavior is distinctly shallow and short compared to other penguin species, which is an adaptation to their near-shore foraging habitat. Most hunting dives last less than one minute and reach depths of only about 6 meters. Although the maximum recorded dive depth can exceed 50 meters, the majority of foraging time is spent near the surface where the small schooling fish are concentrated. This shallow diving minimizes energy expenditure in the warm equatorial waters.
Foraging trips are typically limited in distance, with birds rarely venturing more than a few kilometers from their nesting sites on the western islands. This restricted range is possible because the nutrient-rich Cromwell Current provides a reliable, localized food supply close to the coastlines of Isabela and Fernandina islands. A typical foraging trip lasts about eight hours, demonstrating concentrated, efficient hunting near their home base. This short duration also allows them to return frequently to cool off or feed chicks.
Impact of Ocean Conditions on Food Supply
The stability of the Galapagos penguin’s diet is fundamentally linked to the presence of cold, nutrient-bearing ocean currents. The Equatorial Undercurrent (Cromwell Current) flows eastward below the surface and upwells when it meets the western islands, bringing deep, cold water and nutrients to the surface. This upwelling supports the phytoplankton bloom that forms the base of the marine food web, sustaining the small fish the penguins consume.
This delicate balance is severely disrupted by large-scale climate phenomena, most notably the El Niño-Southern Oscillation (ENSO) events. During an El Niño, the surface waters of the eastern Pacific warm significantly, and the trade winds that drive the upwelling weaken. This causes the layer of cold, nutrient-rich water to sink deeper, effectively cutting off the food supply to the surface.
The resulting scarcity of cold-water fish like sardines leads to severe food shortages for the penguins. Without their primary food source, adult penguins often abandon breeding attempts to ensure their survival or suffer high mortality rates. Historical El Niño events, such as those in 1982–83 and 1997–98, correlated with population declines of 65% to over 75%. This demonstrates the profound ecological vulnerability of this equatorial species to changes in ocean temperature.