La situacion alimentaria del Jurel Trachurus murphryi Nichols en un año normal (1979) y en el niño 1982/83

Abstract

The feeding conditions of horse mackerel (Trachurus murphyi) during a “normal” year (1979) and during El Niño 1982/83 have been studied in the areas of Paita, Callao, Pisco and Ilo analyzing data about (1) diet composition, (2) feeding index and (3) length/weight relationship (n = 2082).

During El Niño the most notable change in diet composition was the almost total absence (< 5%) of anchovy (Engraulis ringens) which was, in 1979 with more than 60% of the total stomach weight, the principal food item (mean: Callao, Pisco, Ilo). Unlike central and Southern Peru, the importance of anchovy as horse mackerel’s food-resource was almost zero in the North (area of Paita: 4° L.S – 7° L.S) not only during El Niño 82/83, but also during the “normal” year 1979.

Diet diversity was increasing during El Niño because of the occurrence of fishes from tropical regions like Bregmaceros bathymaster, Abrialopsis sp. and the fraction of macrozooplankton (copepodes, eufausidos), which in 1979 was of 36%, became with 53% of total stomach weight the most important one.

During El Niño the feeding index was only 36% of the mean value estimated in 1979 and the length/weight relationship analysis indicates an 8% loss in weight for a 35 cm male when compared with the 1979 data.