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

Hugo Arancibia,Sergio Neira

doi:10.3989/scimar.2005.69n2295

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 Nino 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.

Highlights

The mean trophic level of fishery landings (TLm) has been proposed by Pauly et al (1998) as an index of the impact of fishing
TLm has showed a decreasing trend for the last 45 years as a result of a gradual transition in landings from piscivorous, long-lived and high trophic level species to short-lived and low trophic level species. This phenomenon is called ‘fishing down the food webs’ (FDFW) and, in an initial stage the transition in target species produces an increase in landings, followed in a more advanced stage by a decrease in landings that could reflect fishery-induced changes at the community and ecosystem levels (Pauly et al, 1998)
The objectives of the present study are: i) to examine long-term changes in TLm of fishery landings from Central Chile, ii) to determine whether the long term trend of TLm in Central Chile has been masked by landings of horse mackerel, and iii) to determine whether changes in TLm are influenced by El Niño Southern Oscillation (ENSO) events

Summary

Introduction

The mean trophic level of fishery landings (TLm) has been proposed by Pauly et al (1998) as an index of the impact of fishing. TLm has showed a decreasing trend for the last 45 years as a result of a gradual transition in landings from piscivorous, long-lived and high trophic level species to short-lived and low trophic level species (i.e. planktivorous pelagic fish and crustaceans). This phenomenon is called ‘fishing down the food webs’ (FDFW) and, in an initial stage the transition in target species produces an increase in landings, followed in a more advanced stage by a decrease in landings that could reflect fishery-induced changes at the community and ecosystem levels (Pauly et al, 1998). Considering the complexity and high regional variability in world fisheries (Botsford et al, 1997), analyses are needed to test whether FDFW is occurring in more local fisheries.

Objectives

Methods

Results

Discussion

Conclusion