What the Riverfly Census Report tells us - and what all of us should do next

21/06/2016

The Riverfly Census Report for 2015 has mostly been very well received.  There are some exceptions to that, which I’ll come back to later, but first, let’s look at some of the main Census results.

The most important message comes from the fact that the River (Hampshire) Avon was the best performing in terms of its invertebrate species richness and abundance.  The reason, we believe, is an accident of geography, in that the Avon has flowed over Salisbury Plain for several miles above the sampling points.  The Plain is the preserve of the Ministry of Defence and so anthropogenic impact is kept to a minimum – there is no intensive farming, for instance – resulting in less stressors to damage invertebrates.

Although not included in the Census, Dr Nick Everall, who collected and analysed our samples, also did some similar work on a stretch of the Middle Test and showed that sensitive riverside farming can result in improving inverts very quickly.  Water quality at the top of the stretch wasn’t great, but by the time it reached the bottom of the beat, it had improved enough to allow both invert species and abundance to rally quite dramatically.

So, the overall message is simple – cut down on human impact and river ecosystems can look after themselves very well.  Inverts, fish and all other wildlife do not need managing – it is we humans who need the management.

The other glaring conclusion from the Census data is that sediment and excess nutrients – specifically phosphate – are the most dangerous stressors for inverts, and when both work in tandem, the results can be lethal.  We are supporting research into why this is and the results are due to be written up shortly – something to do with anchor points and fungus.  Watch this space.

Now to one or two detractors.  Ignoring one in particular who is more interested in selling fishing on the chalkstreams than their long-term protection, a few scientists have remarked that, while the overall science is credible, our interpretation might be a bit awry in places.

I’ve no problem with discussing the results – on the contrary, the more discussion we have with decision makers means that the Census is having an impact.  What we do want people to do, though, is not to argue the toss over the minutest detail of the Census data, but to look at the wider picture.

In particular, it is the missing species which are as important as some of the numbers.  Where are the blue winged olives and iron blues, the artificials of which were once the staple go-to flies for many flyfishers?  To quote from the Census Report:

Whether it is a rainforest, tundra, coral reef or wetlands like a river, a stream or a lake... reduced species richness is the most consistent indicator of ecosystem distress. It is one of those refreshing simplifications that natural systems, despite their diversity, respond to stress in very similar ways’.
 Clements, W.H. and Newman, M.C. (2002).

As to abundance, it is perfectly obvious that, even if you include substantial error bars on the graphs, many of our rivers are in poor ecological health – the EA even admits to merely 17% of all English rivers being ‘good’ ecologically - and we need some serious commitment from local and national decision makers to firstly acknowledge the situation, and then to do something about it.  We don’t need more plans – we know the problems and we know at least some of the solutions.  What we need now is action, and that will be S&TC’s influencing focus for the foreseeable future - along with more evidence from the continuing Census analytics, of course.  

Image:   Kick samples being analysed on the river bank