Abstract

This paper assesses changes in the southern Humboldt system (33-39 degrees S) in the 20th century by constructing and comparing food web models representing four historical periods: (i) lightly exploited (<1900s), (ii) altered by removal of marine mammals (1950), (iii) development of industrial fisheries (1992), and (iv) the more recent state (2005) when main stocks are fully or overexploited. Models are constructed with a standard structure in terms of functional groups using the Ecopath with Ecosim (EwE) software version 5.1. Model components include: the fisheries, cetaceans, sea lions, marine birds, cephalopods, large-sized pelagic fish (swordfish), medium-sized pelagic fish (e.g., horse mackerel, mackerel, and Pacific grenadier), small-sized pelagic fish (e.g., anchovy and Araucanian herring), demersal fish (e.g., Chilean hake, black conger-eel), benthic invertebrates (red squat lobster, yellow squat lobster, pink shrimp) and other groups such as zooplankton, phytoplankton and detritus. Input data are gathered from published and unpublished (grey) literature. Inter-model comparison is based on individual and community indicators obtained by means of network analysis. The biomasses of target species (with the exception of small pelagic fish) and top predators decrease in more recent models. Although predation mortality is the main cause of total mortality for the majority of the fish groups in all models, fishing mortality of target species is high in the 1992 and 2005 models. This has led to a decrease in the importance of predation removal of the most important fish stocks compared with fishing, which is found to assume the role of the main predator in the system in the more recent state. Changes in system energetics could have resulted in loss of productivity by increased flow to detritus. Prior to heavy fishing, long-living and high-trophic level species were abundant compared to the most recent models in which species with small body size, short life span and low trophic level dominate. These fishing-induced trends are in accordance with what is theoretically expected in stressed ecosystems and, if correct, the food web could now be more susceptible to external forcing and negative ecological interactions. (C) 2014 Elsevier B.V. All rights reserved.