Hugo Arancibia¹, Sergio Neira²

¹Departamento de Oceanografía, Universiad de
Concepción, PO Box 160-C, Concepción, Chile,
E-mail: harancib@udec.cl
²Programa de Magister en Ciencias Mención
Pesquerías, Universidad de Concepción,
PO Box 160-C, Concepción, Chile,
E-mail: seneira@udec.cl

Objectives

To discover whether ENSO induces changes in recruitment of horse mackerel (Trachurus symmetricus) and to analyse its impact on long-term trend of the trophic level of fishery landings in Central Chile.

Results & Discussion

El Niño Southern Oscillation (ENSO) represents a great part of the inter-annual variability in the whole South Pacific Ocean basin. ENSO influences the dynamics of pelagic fish, i.e. changes in the distributions patterns, physiological alterations, reproductive failure and egg and larva mortality.

In this study we analyse possible effects of ENSO events on recruitment processes in horse mackerel, but also in landings of T. symmetricus, and its impact on the whole community by means of the mean trophic level of landings (TLm).

Recruitment of horse mackerel (fish of age group 0 to 3) is shown in Fig. 1. Peaks of recruitment (years 1882-83, 1987-88, 1992-93 and 1997-98) seem to be closely related with the cold phase of ENSO. Lower recruitment and higher spawning (occuring three years before recruitment) seem to be related with non-El Niño conditions (Fig. 2).

Fig. 1 Recruitment of horse mackerel. Arrows indicate El Niño events.

Fig. 2 Interannual variability of sea surface temperature off Central Chile (source: El Niño 3-4 index, NOAA Center of Climate Prediction). Arrows indicate El Niño events.

The annual mean trophic level of fishery landings (TLm), as an index of the fishery-induced changes in aquatic ecosystems, calculated considering the most important fishing resources in Central Chile, is shown in Fig. 3. An oscillatory trend in TLm is strongly influenced by landings of horse mackerel. Peaks in TLm observed in years 1982 and 1988 are related to El Niño events (Fig. 2). They are explained by the combined reduction in sardine, pilchard and anchovy landings, and recruitment success of horse mackerel. The low values of TLm in years 1979, 1984, 1991, and 1999 (the lowest of the time series) are related to non-El Niño conditions: They are explained mostly by low horse mackerel landings in those years. In fact, at the beginning of the time series (late 70's and early 80's), the fishery of horse mackerel was incipient, while at the end of this series it was highly over-exploited. In 1999, TLm reached the minimum value (TLm=2.67), which was a result of both low landing levels of horse mackerel and increased landings of pilchard and anchovy.

Fig. 3 Mean trophic level of fishery landings in Central Chile (33°S-39°S). Arrows indicate El Niño events.

The results indicate that ENSO warm events have a positive impact on the horse mackerel recruitment process, while ENSO cold events have a negative one. These ENSO-induced changes in horse mackerel recruitment also affect the whole community, as can be observed from the analysis of the long-term trend of TLm. This is explained by the importance of horse mackerel in the system (high biomass and extremely high landings).