QUINN and NEAL: LONG-TERM VARIATIONS IN SOUTHERN OSCILLATION 



a 5-yr research and training project that developed 

 and passed on the technique for hydroacoustic sur- 

 veying of fishery stocks.) Karl Johannesson, FAO 

 team leader at the Centre during the project, men- 

 tioned that one would only have to go back to 1 9 7 3 to 

 find that about 95% of the total pelagic biomass off 

 Peru was anchoveta, but by the end of the project it 

 was about 30% or less. He noted that the whole 

 ecological system had been changed after a brief 

 recovery of the stock in early 1976. It was also noted 

 in the Peruvian fishery that at the same time the 

 decline in the anchoveta stock was being observed, 

 other species, such as sardine and mackerel, began to 

 grow (Ceres 1981). The Centre calibrated its equip- 

 ment for these species, and after several surveys es- 

 timated stocks at between 5 and 8 million tons. 

 Vondruska (1981) noted the sharp fall in Peru's pro- 

 duction and exportation of fishmeal in 1977 and at- 

 tributes it to the adverse effects of both heavy fishing 

 and El Nino in 1976. Over the past 5-6 yr Ceres 

 (1981) reported that the Peruvian anchoveta fishery 

 has operated under a set of regulations covering 

 length of season, size of individual fish taken, and 

 maximum allowable catch. 



The fisheries along the north Chilean coast, like 

 those off Peru, are sensitive to environmental distur- 

 bances (Brandhorst et al. 1968; Canon 1978; Quinn 

 1980b; Caviedes 1981). The Southern Oscillation- 

 related El Nino type conditions affect both fisheries. 

 Table 3 of Vondruska (1981), which extends through 

 1979, shows the combined Peru plus Chile fishmeal 

 production to be particularly low in 1973, 1975, and 

 1977. In both fishery areas, species other than 

 anchoveta (e.g., mackerel, sardines) have become 

 more important over recent years. Off northern C hile 

 there has been a decline in the anchoveta catches 

 since 1970, but there was an extremely steep decline 

 after 1976 (figure 4 of Caviedes 1981). Since recent 

 environmental changes, as represented by the 

 Southern Oscillation index trend (Fig. 1), may have 

 played a significant part in the recent unusual west 

 coast South American fishery changes, we wish to 

 consider them in the light of past history and to deter- 

 mine the cause for the persistently low indices 

 since 1976. 



Background and definition of terms frequently used 

 in this article follow. Southern Oscillation indices 

 (differences in sea level atmospheric pressure be- 

 tween sites located in the South Pacific subtropical 

 high pressure region and the Indonesian equatorial 

 low region) are used to represent the Southern Os- 

 cillation (Quinn 1974; Quinn et al. 1978). In this re- 

 spect it was proposed that they be used to monitor 

 and predict Southern Oscillation-related, short-term 



climatic changes over the equatorial Pacific, the 

 oceanic region off the northwest coast of South 

 America, and the Indonesian region. Although we 

 have used many different indices in our studies, we 

 find the Easter-Darwin, Totegegie-Darwin, and 

 Rapa-Darwin indices to be most effective for follow- 

 ing and assessing developments. Details concerning 

 processing of the index data are included in the 

 following section. 



Hushke (1959) defined El Nino as a warm ocean 

 current setting south along the coast of Ecuador, so 

 called because it generally develops after Christmas. 

 In exceptional years, concurrent with a southerly 

 shift in the tropical rain belt, he stated that the 

 current may extend southward along the coast of 

 Peru to lat. 12°S. When this occurs, he reported that 

 plankton and fish are killed in the coastal waters and 

 a phenomenon somewhat like the red tide of Florida 

 results. Through common usage, most publishers 

 and scientists now refer to El Nino as the exceptional 

 year event of Hushke. Also, on learning more about 

 El Nino and the fishery it affects, the definition has 

 been altered accordingly, since it not only involves 

 the thin southward flowing equatorial surface water 

 layer but an influx of waters from the west and 

 northwest beneath this surface layer. The invading 

 thin surface layer has a significantly lower salinity 

 than the subtropical surface water further to the west 

 of the Peru coast, and it is nutrient depleted unlike 

 the cool, highly productive Peru current and its 

 coastal upwelled waters that usually prevail along the 

 Peruvian coast. These infrequent invasions ordinari- 

 ly set in during the Southern Hemisphere summer 

 season, when sea temperatures are at a seasonal high, 

 but they may set in well into the fall; and the effects 

 may persist for a year or more. Additional symptoms 

 of the stronger El Nino, some or all of which may be 

 noted, are torrential downpours, flood, and erosion in 

 the normally arid coastal lowlands of northern Peru; 

 red tide; invasion by tropical nekton; and mass mor- 

 tality of various marine organisms, including guano 

 birds, sometimes with subsequent decomposition and 

 release of hydrogen sulphide (Wooster 1960). It oc- 

 curs at irregular intervals — may appear 2 yr in suc- 

 cession and then not reappear for another 3-12 yr 

 [refers to the moderate and strong categories of 

 Quinn et al. (1978) which seriously affect the fishery]. 

 El Nino is the regional manifestation of a large-scale 

 ocean-atmosphere fluctuation (Southern Oscillation), 

 and it is brought about by relaxation from a pro- 

 longed period of strong southeast trades (re- 

 presented by rising and high Southern Oscillation 

 indices) (Quinn 1974; Wyrtki 1975). The magnitude 

 of the southeast trade relaxation (as indicated by f all- 



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