Using Ecosystem Models to Evaluate Stock Recovery in Two Hake Species from Chile

Abstract

Common hake (Merluccius gayi) and Southern hake (Merluccius australis) are the most important demersal fish species in central and southern Chile, respectively, sustaining fisheries based on fresh and frozen products for direct human consumption, and they have significant impacts on social and economic indicators (jobs and income) for both artisanal and industrial sectors. These stocks have been overexploited for several years without clear signs of recovery. The Chilean Fishing and Aquaculture Law, from the beginning of February 2013, mandates recovery programs (not yet implemented) for overexploited fisheries based on the ecosystem approach to fisheries. We assess stock recovery in these fisheries using two Ecopath with Ecosim (EwE) models representing coastal food webs from central (33–39°S) and southern Chile (41–57°S), including, in both cases, artisanal and industrial fleets operating in each system. Data on catch value, number of jobs and costs (direct and indirect) for the main fleets were used to run numerical optimization routines built in EwE. With this we obtained the fleet-specific fishing mortality rates that maximize in each model the following objectives: economic (income), social (jobs), mandated recovery (biomass increase to the level that results in the maximum sustainable yield), and ecologic (conservation of ecosystem’s trophic structure). Results indicate that it is not possible to maximize all management objectives at the same time. In fact, maximizing total income and jobs is incompatible with stock recovery and ecosystem conservation, and vice versa maximizing stock recovery and ecosystem structure resulted in less income and jobs compared to the current situation. The objectives of economic and social sustainability are not compatible with the objectives of mandated rebuilding in common hake and in southern hake. This means that it is not possible to recover the biomass of common hake and southern hake (and their ecosystem) without affecting income, jobs and vice versa. The stock dynamics and recovery in common hake and southern hake may be strongly influenced by trophic factors (predator–prey interactions), which are not considered in single-species models currently used to determine the biological acceptable quotas for each species and to evaluate recovery scenarios in both species.