Environmental mechanisms associated with fish kill in a semi-enclosed water body: An integrated numerical modeling approach

Abstract

Fish kill incidents are causing increasing concern to coastal communities globally due to the associated economical, commercial and social impacts. In the Arabian/Persian Gulf, human activities have accelerated to meet the rising demands and the economical ambitions, and are associated with organic and inorganic waste loads linked to algal blooms and fish kills in the receiving environment. Understanding the environmental circumstances associated with these events is crucial for planning and coastal management. This study focuses on Kuwait Bay (in the NW of the Gulf) which has a history of repeated fish kills on multiple scales. A numerical model has been successfully utilized, reproducing the key elements associated with fish kill incidents (hydrodynamics, water quality, and particle tracking) and revealing the transport and mixing time scales associated with the major fish kill incident in the Bay in 2020. The study indicated that the environmental circumstances of fish kills can vary in the Bay, so such incidents must be investigated individually. The large scale fish kill incident was found to be associated with unprecedented waste loads during summer 2020. This coincided with a low dynamic period at critical locations within the Bay. As a result, major hypoxic conditions lasting 15 days occurred along the main axis of the Bay in a manner unusual compared to previous events. The model provided key information on the dissolved oxygen, including the mixing and transport time scales, before, during, and after the event. The transport of the dead fish from the hypoxic front to the shoreline was also modeled. Collectively, model results provided generic coastal management approaches suitable for shallow embayments such as the Bay.