There is little doubt that the fisheries of the Humboldt (Peru) Current (Fig. 15.1) represent the largest in the world, not only if one considers the primary production (Paulik, 1971) and catch potential of its waters (Sharp, 1987), but also in view of recordsetting catches. During the 1960s and early 1970s, these catches comprised nearly 20 percent of the world's landings (Fig. 15.2). Yet, the Humboldt Current that supported such high volumes of fish and nourished an enormous marine ecosystem has been constantly beset by oceanic–climatic oscillations – known as El Niño–Southern Oscillation (ENSO) – that noticeably depressed biological productivity and yield levels.

There have also been ecological perturbations in the historical or geological past, as documented in the pioneering work of Schweigger (1959) which offers revealing details offish, bird, and mammal mortality resulting from pre-1972 El Niño events. DeVries (1987) also provides information about geological findings that hint at past catastrophic perturbations along the western coast of South America. Recent ENSO events have resulted in remarkable variations of fish production in the coastal waters of Peru and Chile, measured in terms of fish landings and biomass estimations. It is certain that the depressed Peruvian catches since 1972 reflect the simultaneous occurrence of overfishing and El Niño (Instituto del Mar del Perú, 1981).