Skip to main content

Bugs in the Cray

Following on from the water quality data analysis - here is some summarised information that TINTT has pulled together using data kindly supplied by the EA. These data are drawn from sites that are being considered for habitat restoration (with a possible long-term view of restoring native trout populations). First of all, it is apparent that there are examples of a number of invertebrate families that are happily living in the Cray that would not be able to exist in polluted environments. You can particularly see the good populations of Gammarus (freshwater shrimp). These shrimp are a valuable find because they have lifecycles that can take two years or more to complete. In addition, because they can't fly, they are not very good at migrating upstream over weirs to colonise new areas (i.e. they can only really re-colonise from upstream populations if they are wiped out). Taken together - their presence in healthy numbers indicates that water quality tends to be good enough to enable them to complete their long lifecycles. They are also a good "year round" supply of protein for fish.
Another interesting pattern is the obvious cycle of Blue Winged Olive (Ephemerellidae) nymphs as they grow to a size that can be captured by the 2-mm sampling net mesh (and are visible to the naked eye!) towards the summer months - and then after mass hatches in summer - decline to become invisible to the samplers during winter (when they are present as eggs or very small nymphs). The apparent decline of Rhyacophila (a predatory caseless caddis) seems to be replaced by an initial increase in the net spinning Hydropsyche (filter-feeding caddis).
Finally - for two sites that are of particular interest in terms of the potential for nearby habitat restoration - these are averaged "biotic index" scores over several years. The big bars are the mean (average) values and the little legs indicate the variability of the figures around that mean (error bars are one "Standard deviation" - which indicates the spread that would capture about 95% of all the individual values that make up the average). BMWP scores use a ranking system based upon the sensitivity of each family to organic pollution. These scores vary between 1 completely tolerant) and 10 (exceptionally sensitive to organic pollution). The score for each individual family that is present in a sample is summed to give the BMWP. The higher the score - the cleaner the water. The average score of each family (ASPT) gives an indication of how many "sensitive" families are present - the closer this value is to 10 the better (although it is never possible that this is the case - because even the cleanest sites are home to tolerant as well as sensitive bugs). Finally, the Number of Taxa is simply the number of different BMWP families that are present in the sample. Overall - the organisms that are present here do not indicate that there is a serious problem with the water quality in these sections of the Cray. They are fairly typical of a stream that is somewhat impacted by urban effluents (compared to a completely pristine rural chalkstream). However, there is no evidence that the scale of impact on the water quality would prevent the survival of salmonid fish at this stage.


Popular posts from this blog

Why Presume to Remove Weirs? (with River Dove Case Study)

Weirs and the Backwards Ways that Rivers Work One of my favourite sayings on river restoration is a mangled quote from a movie

"...boxing is an unnatural act. Everything in boxing is backwards: sometimes the best way to deliver a punch is to step backwards...but step back too far and you ain't fighting at all".

So my mangled version starts out "Everything in rivers is backwards...". Basically, I never seem to run out of new examples of "what SEEMS to happen in a river is actually the complete opposite of what really happens".

The rest of this article looks at many of the "backwards" things about weirs and rivers - and finishes off with a real-world case-study that is playing out right now on the River Dove.

One spoiler alert is that, from an ecological point of view, it is almost always safe to assume that:

The best biological outcome for a river is the removal of some or all of an artificial weir. 
Now, I don't expect you to believe that…

CATCH in Wincanton and News of the First Recorded Wild Brown Trout Following Their Hard Work

Blog posts are like London Buses it seems!

This one is just a very short "Congratulations" to the Folks at CATCH (Community Action to Transform the Cale Habitat) and the video put out by Wincanton Window (embedded below).

All of the folks in the partnership mentioned in the video have done HUGE amounts of work (from classroom education projects to habitat working parties and endless enthusiasm for engaging more people in their local river and much more besides).

A big disclaimer from me is that, although this project is supported by/affiliated with our Trout in the Town project - it has been Mike Blackmore who has fulfilled that role for the WTT rather than myself.

So massive well done to all involved (especially you Gary Hunt!)- it is wonderful to see all of the fish and wildlife coming back to the Cale. Of course, it is absolutely delightful to see that wild brown trout put in an appearance as well!

It seems to be all the rage for recovering urban stream projects in the &q…

Birmingham and Coventry's Urban Waterways

It's about time for a new blog post and I thought it would be good to flag up some of the investigations that I've been doing in conjunction with Waterside Care (which, in itself, is supported by Keep Britain Tidy).

As well as initial investigations on the River Cole around the Shire Country Park and Burberry Brickworks, more recent forays to the little Westley Brook, River Sowe, Stonehouse Brook and a little stream in the Holly Wood Local Nature Reserve (between Great Barr and Queslett) have seen me criss-crossing the M6 and M69 and the surrounding areas.

What always surprises me is just how much of the Black Country/Coventry area is essentially "floating" on a vast network of underground watercourses which suddenly pop up into daylight in surprising places. Of course this puts a lot of pressure onto the biology of these streams - not only from the physical "encasing" of their channels in brick and concrete (both above and below ground).

It is the ever-pre…