Fish and crayfish
A significant amount of the value we place on our of rivers, streams and estuaries centres on their iconic fish and crayfish species, both in terms of the species we target recreationally (such as black bream, marron and prawns) and also as indicators of river health (including negative aspects such as fish kill events). Collecting data on fish and crayfish allows us to monitor these values.
Fish and crayfish are good indicators of river and estuarine condition as they are often top predators and keystone species within the trophic structure, which means that they are closely linked with the overall health of the system. Monitoring the species dynamics, such as changes in species composition, abundance, diversity, health and condition can provide valuable information relating to system health. This can extend to indications of previous disturbance, current condition, including factors such as water and sediment quality, aquatic and riparian vegetation, habitat, barriers to connectivity, altered flow regime and catchment disturbance and overall system stability.
In many cases, monitoring fish and crayfish can provide information which is not captured by other variables. For instance, a reduction or loss of a species which is known to be sensitive to low dissolved oxygen may highlight an underlying problem that may not have been detected by snapshot water quality sampling. For example, low oxygen conditions occurring only in the early morning due to algal blooms, which produce oxygen during the day and consume it during the night. Similarly, a change in age demographic of fish species may highlight an issue with their ability to reproduce, such as a barrier impeding migration of adult fish upstream to breeding grounds.
Fish and crayfish data can also highlight problems stemming from a combination of stressors. That is, where small changes in a number of factors can lead to a large effect on the health of the environment. Different species have different sensitivities to the range of stressors that are known to occur in Western Australian systems, including salinisation, sedimentation, algal blooms, declining water and sediment quality, removal of habitat and altered flow regime. Monitoring individual species can help determine what stressors are impacting the system.