THE FISH RESPONSE ASSESSMENT INDEX (FRAI) AND MACROINVERTEBRATE RESPONSE ASSESSMENT INDEX (MIRAI) AND THEIR ROLES IN AQUATIC ASSESSMENTS AND MONITORING
Aquatic impact assessments and subsequent monitoring are integral components of integrated sustainable management particularly in a developing economy. The main aim of aquatic assessments and monitoring is to determine the Ecological Category (EC) of a receiving or impacted aquatic resource. The overall process is referred to as the “Ecological Classification Process” which refers to ‘the determination and categorisation of the Present Ecological State (PES; health or integrity) of various biophysical attributes of rivers relative [to] the natural or close to the natural reference conditions’ (Kleynhans and Louw, 2007).
The most widely recognised and commonly used measure of determining the EC of a river is through the application of the South African Scoring System: Version 5 (SASS5). The SASS5 protocol was refined by Dickens and Graham (2002) in which aquatic macroinvertebrates are used as a means of determining the ‘health’ or EC of a river. The Macroinvertebrate Response Assessment Index (MIRAI) was developed by Thirion (2007) as a supplementary tool to the SASS5 protocol. According to Thirion (2007), the SASS5 protocol is a very strong indicator of water quality based on the Average Score per Taxa (ASPT) of the macroinvertebrate assemblage sampled at an assessment site. However, Thirion (2007) maintains that the SASS5 protocol does not allow for certain inferences to be made. Therefore, the aim of the MIRAI is to incorporate the results of the SASS5 protocol into a model which also assesses the aquatic habitat/biotopes present at the assessment site. This would allow for a deeper understanding and interpretation of the deviation of the macroinvertebrate assemblage from the reference state.
In simple terms, the MIRAI model requires the user to input a list of reference macroinvertebrates (ie. What species would be expected to occur at a certain assessment site?). The user would then input the results of the SASS5 protocol into the model; this would list what macroinvertebrates were actually present during the infield assessment. The aquatic habitat/biotopes present during the infield assessment would then be compared to what is expected to be there in a reference or undisturbed state. For example, under a reference condition, the banks of a river might be well vegetated providing good marginal vegetation habitat for aquatic macroinvertebrates. Disturbances such as agriculture or vegetation clearance may reduce the availability of marginal vegetation habitat. The user would score changes in habitat availability and diversity from reference to current. In the example given, the user would score a reduction in the availability and diversity of marginal vegetation. In addition to scoring habitat changes, the user would also score habitat preferences of the reference macroinvertebrate species as well as those actually sampled during the assessment. Referring again to the example, a reduction in marginal vegetation will presumably result in fewer macroinvertebrates with a preference for that habitat being present when compared to the reference state.
The MIRAI therefore provides a strong ‘habitat-based cause-and-effect’ basis when attempting to determine why a macroinvertebrate assemblage has changed from its reference (Thirion, 2007). The MIRAI model provides the user with a means of interpreting SASS5 results to a greater depth and complexity. Where the SASS5 protocol makes general inferences about water quality changes at an assessment site, the MIRAI incorporates habitat based changes as well.
The Fish Response Assessment Index (FRAI) is another model that can be used in aquatic assessments and monitoring. FRAI was developed by Kleynhans (2007) and utilises ‘environmental intolerances and preferences’ of fish assemblages at an assessment site. Much like the MIRAI, a reference list of fish species must first be compiled against which to compare what fish species are actually caught at the assessment site. There are various means of catching/sampling fish species but the most commonly used are electro-shocking and the use of a seine net. As with the MIRAI model, habitat preferences and changes from the natural conditions to current are input into the model to determine overall changes in habitat conditions. This coupled with the fish species sampled at the site is used to calculate the overall EC of the fish assemblage. The results of the FRAI and MIRAI can be integrated to determine the Instream EC using the Instream Response Model (Kleynhans, 2007) which provides a holistic overview and understanding of the deviation of current river conditions from the reference or undisturbed state.
Once-off MIRAI and FRAI assessments provide very little data particularly if limited data relating to reference species lists are available for a particular study area. These models provide excellent data and a deep understanding of the changes within a river system over longer periods of time. It is therefore essential that the user of these models carries out sufficient research, whether it be online databases or previous specialist reports, of the study area to compile accurate reference species lists and habitat conditions. These models, in conjunction with others which form part of the EcoClassification Programme, are essential in aquatic assessments and subsequent monitoring.
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References Kleynhans CJ, Louw MD. 2007. Module A: EcoClassification and EcoStatus determination in River EcoClassification: Manual for EcoStatus Determination (version 2). Joint Water Research Commission and Department of Water Affairs and Forestry report.
Kleynhans CJ. , 2007. Module D: Fish Response Assessment Index in River EcoClassification: Manual for EcoStatus Determination (version 2) Joint Water Research Commission and Department of Water Affairs and Forestry report. WRC Report No. TT330/08
Thirion, C. 2007. Module E: Macroinvertebrate Response Assessment Index in River EcoClassification: Manual for EcoStatus Determination (version 2). Joint Water Research Commission and Department of Water Affairs and Forestry report.