Population Trends of the Galápagos Penguin: Impacts of El Niño and La Niña

Abstract

The Galâpagos Penguin (Spheniscus mendiculus) population probably has always been small and largely restricted to the islands of Fernandina and Isabela. Counts suggest the current population of Galâpagos Penguins is likely between 4,250 and 8,500, half of what it was in the early 1970s. Population size has varied and declined probably because of substantial changes in oceanic conditions. Body condition as evidenced by weight is enhanced during cold surface water conditions, La Niña, and deteriorates when surface waters are warmed, El Niño, and under the most severe conditions, penguins starve. Analysis of a long-term data set from counts of the population suggests that the population has fluctuated, dropping precipitously after the 1982-1983 El Niño and has since then been recovering very slowly. This parallels the overall warming in the Pacific during the last 20 years associated with the more frequent El Niño and less frequent La Niña events. These trends suggest that long-term global climate warming is likely to threaten the Galâpagos Penguin population particularly because the population is small and its distribution restricted. New threats from climatic warming and increasing human perturbations such as fishing, inadvertent discharge of petroleum products, and transport of potential predators and pathogens to islands increase the risk of extinction.