The El Niño phenomenon of 1997-98, and the associated massive media coverage, provided a primer on oceanography to millions of people around the world. More than 60 countries suffered heavy floods or severe drought as a result of weather anomalies caused, at least in part, by the phenomenon's cyclical warming of surface waters off the coast of Peru. Between April 1997 and April 1998, floods were reported in over 40 countries, droughts or dry spells in 22 countries and two countries suffered widespread forest fires. Furthermore, countries can be subjected to a double whammy when an El Niño event is immediately followed by a La Niña event. La Niña is characterized by an upwelling of cold water in the areas of the Pacific that may bring drought to areas hit by floods during El Niño, and flooding to those hit by drought.
The combination of El Niño and La Niña events provide extreme examples of environmental variability that made international news almost every day during 1997-98. Reports dealt with the devastating effects of the floods, droughts and forest fires. Fishery resources, although not the object of such media attention, were any less affected.
In fact, as information on variability in fish populations accumulates over long periods, it seems that many of the world's largest fish stocks are growing and declining in relative synchrony. The simultaneous rise and fall of sardine (pilchard) populations in widely separate areas of the Pacific Ocean was first pointed out at the major FAO Expert Consultation in 1983. Since then, the pattern reported has continued to hold, including an additional episode of a simultaneous pattern change from population growth to abrupt decline.
Other examples include the Peruvian anchoveta (which grew to support the largest fishery that has ever existed), the Southern African pilchard fisheries and the Japanese flying squid, which all rose and peaked between the late 1950s and early 1970s during which time the large Pacific pilchard stocks essentially vanished.
The early period from the 1970s to the mid-1980s, which saw the massive rises of sardine stocks in the Pacific and the collapse of the Peruvian anchoveta in the Pacific and the Southern African pilchard in the Atlantic, was also a remarkable period of global average temperature rise, suggesting the likelihood that climatic variability may be the driving force linking these variations. However, it seems unlikely that temperature alone could be the major causal agent, since the sea temperatures on the eastern and western sides of the Pacific Ocean tend to vary out of phase rather than in phase. This was also a time of enhanced El Niño conditions, marked by a long-period progressive collapse of the Southern Oscillation Index, commencing with the 1972 El Niño and culminating in the major 1982-83 El Niño episode.
Clearly, no one is yet sure that these ostensible patterns are anything more than fortuitous happenstance, nor has a comprehensive objective analysis been produced. However, there is no doubt that if there does exist a truly effective climatic linkage mechanism which acts to synchronize variability in many of the largest and most important fish populations of the world, it has very interesting and important implications for management of the global fish supply, food security, and for understanding - even predicting - fishery resource variability.
Whatever its sources might be, natural variability adds to the uncertainty about the working of exploited ecosystems, their resilience to human impacts and their capacity to recover from serious disturbances. It therefore contributes to the need for wide implementation of the precautionary approach to fisheries.