Carrying capacity simulations as a tool for ecosystem-based management of a scallop aquaculture system
Over the past decade, Sechura Bay has become an important center for mariculture in Peru, where the Peruvian bay scallop (Argopecten Purpuratus) is grown in bottom cultures. Currently, the business involves 5000 artisanal fishermen and yields an export value of more than 158 million US$ per year. However,intensity and area extent of cultivation activities continue to increase. Overstocking of scallops combined with critical environmental changes may cause mass mortalities and severe consequences for the ecosystem. Accordingly, the ecosystem-based assessment of the current situation and the determination of long-term sustainable limits to scallop culture for the bay are crucial. Using a trophic food web model,the further expansion of culture activities is explored by forcing scallop biomass to increase to four different levels (458, 829, 1200, and 1572 t km-2) and the impact on other groups and the ecosystem are investigated. The ecological carrying capacity (ECC) is defined as the maximum amount of scallop biomass that would not yet cause any other groups biomass to fall below 10% of its original biomass. Results suggest that (a) the current magnitude of scallop bottom culture (147.4 t km-2) does not yet exceed ECC, (b) phytoplankton availability does not represent a critical factor for culture expansion, (c) a further increase in scallop biomass may cause scallop predator biomasses to increase, representing in turn a top-down control on other groups of the system, and (d) exceeding scallop biomass levels of 458 t km-2may cause other functional groups biomasses to fall below the 10% threshold. The applicability and potential of the here presented ECC simulations as an ecosystem-based approach to sustainable bivalve culture are discussed. Results of this study are expected to guide both local fishers and managers in their challenging task of finding sustainable long-term levels for this important socio-economic activity in Sechura Bay.