A significant amount of the value we place on our of rivers, streams and estuaries centers on the iconic fish and crayfish species that inhabit these waters, both in terms of the species we target recreationally (such as black bream, marron and prawns) and also as icons of river aesthetics (both positive and negative e.g. fish kills ). In addition to the social and economic justifications for monitoring fish and crayfish, there is also a significant environmental argument for their inclusion as sensitive indicators of system health.
Fish and crayfish are often top-down predators and/or keystone species within the trophic structure of a waterway, which means that they are closely linked with the overall health of the system. As such, monitoring the species dynamics (changes in species composition, abundance, diversity, health and condition) can provide valuable information relating to system health, which can extend to indications of previous disturbance, current condition (including factors such as connectivity) and overall system stability.
In many cases, monitoring fish and crayfish can provide information which is not captured in other variables typically determined. For instance, determining contaminants in fish can provide information of chronic water quality problems not captured in snapshot studies; a reduction or loss of a certain species which is unable to tolerate low dissolved oxygen may highlight a typical period of low dissolved oxygen that can occur early in the morning due to algal blooms (not often highlighted with snapshot sampling); or a change in age/size demographic may relate to an interruption to reproduction, such as a fish barrier (weir) impeding migration of adult fish upstream to breeding grounds. Analysis of fish and crayfish can also highlight underlying problems relating to combined effects for example, where a small change in a number of system variables can have a significant cumulative impact.
There are also a number of species that are sensitive to the range of problems that occur in Western Australian systems, including salinisation, sedimentation, pollution, toxic algal blooms, declining water quality, removal of habitat and altered flow regime. Ecotoxicology utilises these ‘indicator’ species to investigate problems both in the field and laboratory.
For more information relating to the health of our waterways in terms of the fish and crayfish that inhabit them see the project links within Assessing river health and Assessing estuary health.