Simulation of fish behavior and mortality in hypoxic water in an enclosed bay

A model of fish preference for environmental conditions (dissolved oxygen (DO) and water temperature) and mortality was developed and coded within a combined hydrothermal and eutrophication model. The model was applied to an enclosed bay located in the western part of Japan, where eutrophication and associated onset of hypoxia at the bottom waters would occur in every summer. A field survey of fish behavior under hypoxic and non-hypoxic waters was conducted by releasing marbled sale in the bay and tracked its movement. At the same time, vertical profiles of DO, salinity and water temperature were measured at every 0.5m vertical interval at several locations along the tracking path of fish. Moreover, a series of preference tests for DO, salinity and temperature in the laboratory were conducted in order to decide preference parameters of fish. The model could simulate reasonably the observed behavior and movement of the fish under both hypoxic and non-hypoxic waters in the bay; thereby, validated its applicability. Using the model, an assessment of the impact of the ongoing land reclamation project of about 400 ha in the bay on the fisheries resources was also conducted. The results showed that a substantial mortality of the fisheries resources would take place when hypoxic condition occurs in every summer and the construction of the artificial land will lower the mortality rate of fish during the summer period in the bay. Strong offshore winds cause the upwelling of bottom hypoxic waters in summer and the initial mortality of the fisheries resources increase under northerly offshore wind of 5 m/s or more.