Comparative analysis of trophic structure of commercial fishery species off Central Chile in 1992 and 1998

Abstract Trophic interactions and community structure of commercial fishery species off Central Chile (33°–39°S) were analyzed and compared for 1992 and 1998 by ecotrophic modelling, using the Ecopath modelling software. The model encompasses the fishery, pinnipeds (sea lions), small pelagic fish (anchovy, pilchard), medium-sized pelagic fish (horse mackerel), demersal fish (e.g. Chilean hake, black conger), benthic invertebrates (carrot prawn, yellow prawn), and other groups such as zooplankton, phytoplankton, and detritus. Input information for the model was gathered from published and unpublished reports and our own estimates. Also, the effects of fishing and predation on fishery resources and on the most important components of the system were investigated, within an ecotrophic framework. Predators consumed the greater part of the production of the most important fishery resources, particularly juvenile stages, and the fishery removed a large fraction of adult production. Mortality by predation is an important component of natural mortality, especially in recruit and prerecruit groups. Analysis of direct and indirect trophic impact shows that adult Chilean hake have a negative impact on juvenile Chilean hake through cannibalism, and on pilchard, anchovy, and carrot prawn through predation. Also, fishing has a strong impact on fishery resources, such as Chilean hake, pilchard, and anchovy. Total biomass in 1998 was 1.5 times higher than in 1992. However, total catches in 1998 were about 80% of those in 1992. Changes in biomass and total yields of the system between 1992 and 1998 can be observed in such properties as total flows, consumption, respiration, and production. It is concluded that ecotrophic modelling is an useful tool for fishery management, since it can improve our understanding of the predator–prey interactions among the exploited (fishery resources) and unexploited but potential fishery resources of the system.

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