Increase in abundance: A dangerously simplistic view of river health

Species richness and assemblage gives a far more accurate assessment of invertebrate communities………..

Dr Janina Gray, Head of Science & Environmental Policy, responds to a recent article in The Times,

Your article Boom in freshwater bugs bucks trend of disappearing insects (April 24th) sets a dangerously simplistic view of the health of our rivers and water life.

The article reports only one metric – increase in abundance – and not the diversity of species present. Species richness and assemblage gives a far more accurate assessment of invertebrate communities and consequently a river’s health.  For instance, our work has shown that chironomid species can have very high abundances, but they are an indicator of poor water quality, and so their abundance/biomass should not be applauded.

Using abundance data is not a metric which can be used to infer ‘bugs are not disappearing’. S&TC’s Riverfly Census, which recorded 34,000 insects from 480 species across 12 English rivers, showed that pesticides, sediment and excess phosphate are adversely impacting all our rivers to some extent, and are especially damaging to our chalkstreams – once the byword for pristine water quality.  We therefore strongly suspect that your article reports false positives on the true state of freshwater biodiversity and health, by inferring an increase in abundance of pollution-tolerant bugs is a good thing. In order to understand the true state of freshwater bugs, studies must use species richness and abundance data together to form an accurate assessment.

Reporting with a purpose

S&TC is a national organisation and we use evidence from local case studies to help instigate policy changes that will benefit UK wild fish populations. But, this is just part of the value - we are making all our Riverfly Census findings available so they can be used to inform local management and drive action.

Each individual river report is based on three years of surveying data. Where possible, we have linked up our findings with other existing literature and data. Using the available information we suggest where local fishing and/or conservation groups can focus their management efforts to achieve the best health outcomes for each of the 12 original Census rivers.

Some of our local reports can be found on the slider below. Alternatively, visit the Riverfly Census page and scroll down to the map.