Long-term changes in the mean trophic level of Central Chile fishery landings

Abstract

We explore long-term changes in the mean trophic level (TLm) of Central Chile fishery landings, using a 21 years data series (1979-1999) of official landings (Chilean Fisheries Service) of 16 species that comprise about 95% of total landing, and their corresponding trophic level estimated using gut content analysis and a trophic model of the Central Chile marine ecosystem. Because total landings off Central Chile have been strongly influenced by landings of horse mackerel (Trachurus symmetricus), which is a trans-zonal fishery resource (sensu FAO), and the periodic occurrence of El Niño Southern Oscillation (ENSO) events in the study area, we explore changes in TLm both excluding landings of horse mackerel and excluding landings in ENSO years. When landings of horse mackerel are excluded, a significant decline in TLm is found, at a rate of 0.175 per decade, which is higher than the global rate of 0.10 estimated by Pauly et al. (1998). Fisheries in Central Chile seem to have been fishing down the food web as the result of fishery-induced changes, since ENSO events do not seem to have induced a significant effect in this trend. Therefore, we suggest that landings of horse mackerel have masked the fishing down the food web process in local fisheries.