Marinda Avenant

Marinda Avenant

Marinda holds a Masters in Environmental Management from the University of the Free State where she lectures in several postgraduate programmes. Her fields of interest include aquatic biomonitoring, environmental water assessments and integrated water management, with a specific focus on non-perennial rivers. Her doctoral study investigates the role of fish communities as indicators in the determination of the water requirements in non-perennial rivers.

The Role of Fish in a Suite of Indicators for Assessing the Environmental Water Requirements of Non-Perennial Rivers: Case Studies from South Africa

Fish are considered very useful biological indicators, and have been used as key indicators in instream flow assessments since the beginning. By law, environmental water assessments (EWAs) in South Africa have to consider the environmental water requirements (EWRs) of the whole ecosystem. The holistic EWA methodologies developed in South Africa therefore make use of a suite of indicators that include biological response indicators such as riparian vegetation, aquatic macroinvertebrates and fish communities. Previous studies have shown that existing methods have been developed for use in perennial rivers, and are ill-suited for use in non-perennial rivers. A multi-disciplinary team under the leadership of the Centre for Environmental Management has developed DRIFT-Arid, a dedicated methodology for determining EWRs in NP rivers, over a period of eight years. It is a comprehensive, multi-disciplinary approach that captures specialists’ knowledge of a catchment in a structured database that is then used to predict the ecological and socio-economic impacts of future flow management options. Central to the method is the selection of a range of indicators that captures the unique attributes of a river ecosystem. Predictions are made on how these indicators are likely to respond to changes in the flow regime, as well as to changes induced by other indicators. This approach was successfully tested on an ephemeral tributary of the Orange River, the Seekoei, and a semi-permanent tributary of the Limpopo River, the Mokolo. This contribution focuses on the role of fish communities in assessing the EWRs in NP rivers. The practicality and usefulness of including fish as an indicator in southern African NP rivers are assessed. Fish communities in these systems are depauperate and hardy with generalised environmental requirements. Associated constraints, including difficulties with using score-based methods, are discussed and the inclusion of fish in the suite of indicators is motivated.

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