| Sumario: | A study was conducted to examine uncertain biomass shifts in renewable resources. A biomass shift takes place when a dominant renewable resource stock collapses and its ecosystem niche is filled by a replacement species that increase in abundance following the initial collapse. A bioeconomic model for a fishery facing random biomass shift is developed. Optimal policy for three causes of biomass shift—environmental perturbation, overfishing, and a combination of these two factors—is derived and compared to optimal policy when the risk of biomass shift is absent. For each of the three causes of biomass shift, the model allows for a valued and non-valued replacement species. It was found that where a biomass shift is due solely to an exogenous environmental perturbation, optimal exploitation is faster than where there is no chance of biomass shift. Where initial collapse is caused solely by overfishing, optimal exploitation is slower than in the no-collapse case. However, in the presence of a valued replacement species, optimal exploitation of the initial species increases.
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