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vol.30 número1  suppl.SympIs the jack mackerel population affected by ENSO's variability?The 1997/98 El Niño in the Humboldt Current System: a Synthesis índice de autoresíndice de materiabúsqueda de artículos
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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002

http://dx.doi.org/10.4067/S0717-71782002030100077 

El Niño 1982-1983 and 1997-1998:
Effects on Peruvian Jack Mackerel and
Peruvian Chub Mackerel

Teobaldo Dioses, Rosa Dávalos,
Jorge Zuzunaga

Instituto del Mar del Perú, Apartado 22, Callao, Perú,
E-mail: tdioses@imarpe.gob.pe, rosa_davalos@hotmail.com,
azuzunaga@imarpe.gob.pe

Jack mackerel and Chub mackerel are resources related to the variation and interaction of surface and sub-surface water masses that exist off the Peruvian coast. Jack mackerel live in the oceanographic front formed by Sub-tropical Surface Waters (SSW) and Cold Coastal Waters (CCW); whereas Chub mackerel live are associated with Equatorial Surface Waters (SEW). Under "non-normal" conditions like El Niño, the distribution and concentration of these resources depends on which water mass is dominant and to what extent.

In order to explain how this phenomenon influences these resources, we have considered variables like landing data, Fulton condition (FC), gonadosomatic index (GSI) and vertical distribution of these species during the last two stronger El Niño: 1982-83 and 1997-98.

El Niño 1982-83 began in June 1982 with a weak heating, then an extreme abnormal increase of surface temperature between September 1982 and June 1983. At that time, warm waters of low salinity, Tropical Surface Waters (TSW) and ESW, came from the north and moved to 14°S in 1983. However, between December1982 and October 1983 SSW covered a major area of the Peruvian Sea.

During El Niño 1997-98, specifically in March and April, ESW moved to the central region of Peru, and at the same time SSW approached the coast. During 1998, SSW became stronger with higher salinity values, which had never been seen before off our coast (35,9 psu), whereas Sub-Antarctic Temperate Waters (STW) moved to the north of Callao, forming the main traits of this El Niño.

Jack mackerel and Chub mackerel were affected by this phenomenon in different ways. The Northern _ Central region was the most strongly affected because warm waters with low salinity approached the coast, while the southern region was more influenced by oceanic waters. Concentrations of Jack mackerel were more available near the coast because SSW advanced eastward; commonly this species inhabits areas 100 nm offshore. At the beginning of 1982 a biomass of 6,0 million tons was estimated, and by March 1983 there were 6,8 million tons. On the other hand, during El Niño 1997-1998 SSW were not very close to the coast which explained why the estimated biomass was lower; 1,6 million tons in 1997 and only 62 thousand tons in 1998.


Normally, landings of Jack mackerel and Chub mackerel tend to increase in spring and summer, whereas in autumn and winter they decrease. In 1982 the total catch of Jack mackerel was 50 013 tons. Higher numbers were caught from January to April, but for the rest of the year they were poor. This situation continued until June 1983, improving from August to December. The annual catch was 60 772 tones. During 1997, monthly catches of Jack mackerel started to increase in autumn (May) and during winter (August, September) with landings of over 40 thousand tons per month. The total catch at the end of the year was 348 294 tons. From January to September 1998 the monthly catches were poor, improving in spring (October, November and December), with 340 000 tons captured by the end of the year.

The effects of El Niño 1982-83 on Chub mackerel were not very strong because of the low levels of its catches per month. In 1982 these catches were lower than 2,5 thousand tons, and in 1983 they were still lower, with a peak of 1,4 thousand tones. El Niño 1997-98, however, was favourable for this resource since it started, with the best catches obtained in August and September 1997 and a total catch of 181 541 tons by the end of the year. In 1998, landings increased to a record 383 000 tons. The best catches per month were in February and in spring (October, November and December). In December, 145 920 tons were caught.

Owing to physical, chemical and biological alterations which take place in the Peruvian Sea during El Niño, the two species we have studied here suffer a lost in weight. This lost is observed in the FC values. During 1983, the FC for Jack mackerel was 0,901 in the south region and 0,921 in the north region. In 1998, the value for the same species in the north region was 0,698. In 1983, the value of FC for Chub mackerel in the south region was 0,859, whereas in the south region was 1,32. During 1998 the FC was 1,25 for the entire coast. According to these values, the weight of Jack mackerel during these two El Niño events was below the normal average, mainly because food was very scarce and this species was far from its habitat. On other hand, it was very good for Chub mackerel, especially El Niño 1997-98, because incursion of SEW was stronger.

In general, values of GSI for Jack mackerel are irregular and low. We could not perform any analyses because the spawning area is not sampled. It is important to say how the reproductive activity of Chub mackerel varies according to these phenomena. Normally, this specie spawns in summer (from January to March) with more intensity and has a short spawning between winter and spring. During 1997, parallel to the arrival of SEW, the peak of the spawning was in March and it decreased by April. The GSI started to increase in May, giving a second peak in August. The last peak was higher than the first one.

In 1998, the peak of the spawning was in March and a second one, of low intensity, occurred in July. The values of the GSI then decreased at the same time as the Post El Niño stage began. Finally, in December this index started to increase for the spawning period of summer 1999.

During El Niño 1982-83, STW were stronger than SEW, so Jack mackerel was found deeper than 100 m (still 300 m). El Niño 1997-98 was characterized by the unusual presence of monospecific schools of Chub mackerel and a great area of distribution in waters of the Peruvian Sea. Both species were found in ranges of temperature and salinity of 15 to 25°C and from 34,8 to 35,2 psu, respectively. Jack mackerel was found up to 175 m depth, and Chub mackerel up to 100 m depth. Best catches were recorded between 04 and 60 m depth.

Finally, we can say that these two strong El Niño events in the last 50 years influenced both Jack mackerel and Chub mackerel in different ways. The 1982-1983 event was more favourable to Jack mackerel, while El Niño 1997-98 positively influenced Chub mackerel.

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