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This classification method encompasses fish abundance, taxonomic composition and age structure. The tool relates the number of salmon and trout caught in a survey to the predicted abundance and prevalence of the species at the specific site.
Macrophytes provide habitats for fish and smaller animals; they bind sediments, protect banks, absorb nutrients and provide oxygenation. Macrophytes can indicate the impact of increased nutrients in lakes and are also influenced by other pressures such as water level change or acidification.
Estuarine fish communities are good indicators of a range of man-made disturbances. They are mobile, relatively long lived, found near to the top of the food chain (so are affected by other parts of the chain and prone to bioaccumulation effects) and are easy to identify and return to the water: all of these characteristics make them ideal for the monitoring of estuaries. This method is based on the principle that the abundance of fish and the number of individual species found can change depending on the pressures on the estuary.
Benthic invertebrate communities are good indicators of acidification which is caused by acidic pollution from precipitation and acids leaching from the surrounding soils. They are easily suited to biological monitoring as they are common, widespread and easily sampled.