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Investigaciones marinas

versión On-line ISSN 0717-7178

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

Changes in the Distribution,
Abundance and Spawning Season of the
Anchovy Cetengraulis mysticetus, in the
Pacific Ocean off Colombia during the
Events of El Niño and La Niña

Beatriz Susana Beltrán-León

National Institute of Fisheries and Aquaculture -INPA-,
P. O. Box 10742. Buenaventura, Colombia,

The main existing resource among small pelagic fishes, and currently the most captured species in the Colombian Pacific Ocean is the anchovy Cetengraulis mysticetus (Gunther, 1866), which is used mainly to produce fish meal and fish oil.

Barrett and Howard (1961), and Maldonado and Remolina (1976) consider this anchovy as a total spawner between October and February, and Zapata (1992) reported a spawning season between November and December with a peak spawning season in the second half of November for normal years (no Niño nor Niña). According to Zapata (1992) C. mysticetus represents 97% of the total capture dedicated to production of fish meal, which is in accordance with the distribution and abundance of these species' fish larvae.

This study shows how the anchovy adopted a strategy of fractioning the spawning season in response to the environmental changes caused by the events of El Niño and La Niña. The Fisheries and Aquaculture National Institute from Colombia, and the Fisheries Program of the European Union CEE-PEC ALA/87/21 for small pelagic fishes studied the reproductive behavior of the anchovy in normal years and its response to environmental changes, during the research vessel trips of 1991, 1993 and 1994, and the monitoring trips from 1993 to 2002.

Results show that, in normal years, the Gonadosomatic index (GSI) of C. mysticetus maintains low values from February to June, and increases from July until October-November, when the peak spawning season take place, then decreases strongly in December-January. On the other hand, the Hepatosomatic Index (HSI) has an oscillating behavior during the whole year, but opposes the GSI. The condition factor (K) remains stable with a little decrease during October-December (Zapata 1992). This normal pattern coincides with the find ings for the Ichthyoplankton of the anchovy. However, during the events of El Niño and La Niña, a decrease was observed in the distribution and abundance of fish larvae, as well as several peak spawning seasons through out the year, which is not normal, since this species is considered a total spawner. Depending on how intense the event was, the behaviour was maintained for about two to three years after the event finished, and then gradually returned to the normal trend of a single peak- spawning season at the end of the year increasing its abundance significantly. The response of the anchovy is similar whether the event is El Niño or La Niña, but if the events occur directly after one another, as in 1997, 1998 and 1999, the abundance is dramatically reduced.

Analyses of the samples taken from 1991 to 2002 reveal a response pattern of the anchovy to El Niño 91-93 and 97-98 and La Niña 98-99 in terms of spawning grounds. In normal conditions, the anchovy spawns in three zones between Charambirá (Chocó, Colombia) and Tumaco (Nariño, Colombia), usually within 10 nm from the coastline. During and after the environmental changes (Niño or Niña), the spawning grounds were expanded to the north, up to Cabo Corrientes (North of the Colombian pacific coast). Decreases in larval concentrations were also observed, and these were worst when the events happened one after the other (1997,1998 and 1999), with maximum values of 430 larvae/10m2 in 2001 and 269 larvae/10m2 in 2000 (Fig. 1). These values are actually lower than those found in previous years (Beltrán 1993, Beltrán et al. 1994, Beltrán et al. 1995, Beltrán et al. 1996). When normal conditions returned, concentrations increased to over 2330 larvae/10m2, surely leading to a quick recovery of the fish resource (Beltrán et al. 1997).

Fig. 1 Variation in C. mysticetus larvae during 1999-2002 in the Colombian Pacific ocean

During El Niño and La Niña conditions all reproductive indices were reduced in anchovy adults, especially the HSI which decreased drastically, maybe because the anchovy did not feed well and fishes were taking energy reserves from the liver to satisfy their metabolic needs, which in turn affected reproduction (small spawning). This is in agreement with the statement of Schaefer (1987) that environmental temperature changes affect the monthly metabolic system of fishes. Another aspect that was influenced by environmental changes is survival of eggs and larvae, since the success or failure of the year classes is generally determined during the first stages of the fishes life cycle (Howard & Landa, 1958).

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