Trout in the Town Blog

29/09/2014 - 20:56

Here is a video showing just one of a long series of ongoing surveys on a site that was impacted by dredging activities. The Environment Agency re-introduced large boulders and also installed some marginal plants to help the site to begin to recover. Subsequent to that, volunteers from SPRITE- a group set up in Sheffield through the Trout in the Town project applied for permission and carried out re-planting of water crowfoot to improve the structural and invertebrate community diversity within the channel. The method for doing this in spate rivers is highly original and was developed primarily by Dave Woodhead - a central and long-standing SPRITE member, with Ranunculus collection from biologically clean headwater sites and planting work parties being run by Dave and Paul Hughes.

SPRITE also carried out some wildflower seed planting and have joined with other local volunteers to reduce the amount of Himalayan Balsam in reaches upstream of this section.

The video shows how important complex submerged cover is to trout (especially). In much simpler habitat almost all of the trout would have been caught at the upstream barrier after the activity of the survey team had flushed them all the way up through simple habitat that lacked refuge opportunities. However, whilst Ranunculus does not provide much defense against being stunned by a small electric field it (and other complex submerged cover such as tree roots, submerged fallen tree crowns and root wads) does provide significantly improved protection against natural visual predators.

Studies have shown that fish-eating bird predation efficiency drops greatly in the presence of complex submerged cover - and predators give up after a shorter duration to try elsewhere because their calorific return for the energy they need to expend to catch more prey makes the effort unprofitable.

Check out Richard Noble's survey team in action in the video above and see the fruits of volunteer labour (and note how most of the trout that are caught in the middle of the reach are hugging the Ranunculus!). This water plant is also excellent habitat for a number of aquatic invertebrate species and can contribute to improved diversity in flow velocities and associated substrate particle and nutrient-sorting over the cross-section of a channel.

18/09/2014 - 12:26

I was fortunate enough to contribute to Tuesday's launch event for the mammoth achievements that have been made (both in the river channel and within the local community) around Greater Manchester's River Medlock (see this piece from the BBC last year reporting part-way through the initial works

Although a great many people have contributed both to the overall project (and to Tuesday's launch event) - a lot of credit has to go to key personnel like Ollie Southgate of the E.A., Jo Fraser of Groundwork and Dave Barlow of Manchester City Council. The ongoing success of this project owes a lot to their drive and vision - both in the brutally difficult world of making such challenging projects actually happen in the modern economic and social climate and in the amount of effort to involve local communities by reconnecting people with their local river.

For my part I had the highly enjoyable task of introducing local primary school kids to the wonders of fly fishing (in this case Japanese fly fishing - known as tenkara!) in a river that, until recently, had been a smooth brick-lined chute that fish found it impossible to hold station against the current. Now, we might have only had minnows trying to take the fly, but that didn't matter because the kids really enjoyed trying their hand at casting, landing "Freddie the Rubber Fish"(!) and also fly tying. The kids and the fishing demos kept myself and Tom Bird well occupied in the hot late-summer sunshine (glorious!). The kids' experience with fishing and fly tying was coupled with an introduction to the real live invertebrates now inhabiting the channel by Matt Schofield of Irwell Rivers Trust.

After the kids had left, myself and Tom went on a hunt for a wild urban trout - but sadly for us - we didn't manage to find one on this visit. Who knows though, perhaps in time (and with the removal of the remaining kilometer or so (!) of brick channel-lining) we might see some more fish finding their way into this section of river.

07/09/2014 - 18:47

Look what the Wandle Trust have achieved now.

The major connectivity AND channel habitat morphology improvements are hugely significant milestones in the ongoing assisted recovery of this London chalkstream.

It is, also, on the site of the impounded reach I used on this video to illustrate the problems that weirs pose for habitat quality (not only fish passage, but river corridor biodiversity as  whole).


I'm looking forward to going back to take some footage of the 'after' shot :-)


13/08/2014 - 12:46

Each year the WTT hosts a weekend event of talks, food, drink and fishing. This June's Annual Get Together (for members and non-members alike), saw some terrific talks from all speakers. Perhaps the one that surprised the audience the most is the one that is reproduced in full in the video below. A wide-ranging talk that drew on Professor Wotton's fascinating research career on how vitally important to life in rivers (and also all aspects of human existence - from tooth decay to safe drinking water!) are the tiny, stringy "chains" of molecules exuded by cells at the microscopic level.

Now retired, Roger Wotton can look back across a career of teaching and learning to give us a great "taster menu" of anecdotes relating to the surprising invisible world around us. From fish, to invertebrates to the way that classic chalkstream water weeds orchestrate themselves a supply of slow-release fertiliser right on top of their root stock (whilst keeping their leaves swaying just sub-surface for maximum photosynthesis) - the 25 minute talk has it all. Make sure to watch it right the way through because there are wonders of the natural and human world explained like never before throughout (like the answer to how the feat mentioned in the title of this post is achieved!!) - all offered in a wry, dry delivery of which Peter Ustinov would have been proud.


04/07/2014 - 13:45

Back in 2010 the photo above is what an area of Sheffield's urban River Don looked like. Later that year, local Trout in the Town group "SPRITE" organised a day that combined their own volunteer force with a group of University of Sheffield staff that had been released for the day to contribute to volunteer works in the local area. The volunteers cleared a substantial section of the urban Don of all the balsam that they could get their hands on. You can see that, where the balsam had been removed, there was not much else in the way of vegetation that was able to survive...

Then in 2011, as the video below shows, one of SPRITE's activities was to follow up on previous clearance work by removing any re-growth of balsam and then to consolidate that with sowing of a seed-mix of species native to the Don corridor.

SPRITE Winter Working Parties from Paul Gaskell on Vimeo.

Now, in 2014, the photographs below clearly tell the story of how local volunteer action has significantly improved the floral (and associated faunal) biodiversity within the river corridor. These benefits, initiated in 2010 have persisted at least 4 years and counting...Just a small amount of continuing ongoing care will readily control any re-establishment attempts made by balsam seed being imported into this reach. REMEMBER - work that has been noted in this blog previously ( tells us that winning local-scale battles to preserve native biodiversity adds up to a significant conservation of overall biodiversity at landscape scales too. The work to control local patches of balsam, and its results show below, on the Don show that whilst the overall ideal scenario would be to systematically tackle all invasive plants from the top of the catchment downstream, there are still significant benefits to tackling local patches. This is true even with a future potential for re-invasion since there is still a substantial benefit to be had during the period between clearance and re-invasion (in this case at least 4 years)...AND it is much easier to "stay on top of" picking off a low number of re-invading plants than the initial great effort required to clear a large infestation that has already got out of control.

See the pictures below and ask yourself whether, even though there are sources of balsam upstream, the effort has been worth it so far...


20/05/2014 - 15:25

In just one of many illustrative examples in his book "Antifragile - things that gain from disorder" author Nassim Taleb talks about the irony of sports-shoe makers touting that their most advanced models are those that most closely replicate the bare human foot. This is fascinating since it highlights that attempting to smooth out and cushion the shocks experienced during running actually had the effect of massively increasing muscular and skeletal injuries from running.

In barefoot running, the toes and arches of the feet act as shock absorbers and - crucially - allows them to be exposed to the action of running that actually strengthens them in this function. By contrast, the attempt to eliminate those specific stresses resulted in humans striking the floor with their heels rather than their toes and the additional padding robbed our feet of the varied "training" that prevents things like fallen arches and plantar fasciitus.

Another example favoured by Nassim Taleb is that of "regulators"; devices that were fitted to smooth out some of the slightly erratic running of steam engines. The idea was to make them more efficient - and for much of the time this is the effect that they had. However, on the odd occasion, the regulators would get locked in to destructive cycles of inappropriate corrections - and cause the engine to run disastrously/explosively out of control!

In fact, Taleb's book compiles a fat list of examples in which an attempt to rid systems of the natural variability (or in his words "sucking randomness out to the last drop") results in periods of apparent comfort and stability - followed by catastrophic "blow up" or "extinction" events. Those examples are drawn from an impressive array of (seemingly) totally unrelated domains from finance (stock market crashes), through parenting (minor scrapes and bruises are good for kids' development), to careers (a position in a large corporation seems more stable than being a cab driver with variable fares - right up until the corporation makes you redundant).

For me - his writings on these attempts to smooth out randomness which result in periods of stability followed by catastrophe chime very much with lots of efforts to manage flood risk by modifying river channels. There is a certain appeal to the thought that by smoothing and speeding the flow of water out to sea,the risk of it spilling out of its banks should be reduced. But is that a safe assumption to make in the built environment?? In practice that assumption can prove to be catastrophically misplaced. For instance Robert E. Criss and Everett L. Shock's paper "Flood enhancement through flood control" Geology, October, 2001, v. 29, p. 875-878 attributes the increased flooding magnitude and frequency to the engineered channelization that was designed to smooth out and reduce the threat from flooding.

Similarly, I am keen to highlight at any given opportunity the potential responses of river channels when they are dredged to produce dimensions over and above the capacity established through natural erosion and deposition processes:

Essentially - in common with financial markets and steam engine regulators - there are often hidden downsides to naive interventions in the movement of floodwater through a catchment. Those hidden downsides are generally large enough to wipe out (by many, many times over) any benefits that may have accrued during the period of relative (and illusory) stability...Again, this is true of financial trading just as much as it is true of counter-terrorism or - indeed - efforts to increase and smooth floodwater conveyance upstream of hydraulic bottlenecks...

Daniel Kahneman writes (for example in his book "Thinking, Fast and Slow) with consumate persuasiveness and good sense on how we, as humans, are predisposed to defaulting to belief in representations of the world that consist of a simple story. In fact, we are far more likely to believe something that we can form into a simple narrative than an opposing view backed up by hard, objective evidence. Consequently, we treat sharks as more dangerous than traffic - despite what we know about road death and shark attack statistics...

Professor Kahneman uses the phrase "cognitive ease" to describe the state in which we readily accept notions so long as our brains can construct some kind of story around them. It is this state that makes us extremely vulnerable to errors in reasoning (or cognitive traps) - as illustrated by the fact that we will always feel that a 90% fat free yoghurt has to be much healthier than a yoghurt advertised under the tag-line "10% of this product is pure fat". In the same way, we find it nearly impossible (unless we really force ourselves to sit down and think about it) to resist the following cognitive trap - which came to be known as "The Linda Problem":

Participants in the experiment were told about an imaginary young woman named Linda, who is single, outspoken and very bright, and who, as a student, was deeply concerned with issues of discrimination and social justice. The participants were then asked which was more probable: (1) Linda is a bank teller. Or (2) Linda is a bank teller and is active in the feminist movement.”

The overwhelming response was that (2) was more probable; in other words, that given the background information furnished, “feminist bank teller” was more likely than “bank teller. However - this cannot possibly be true; every single feminist bank teller is (of course) a bank teller - but there are lots of additional bank tellers that will not be active feminists. It is the same as saying "Linda is a red haired bank teller" is more likely than the statement "Linda is a bank teller who could have any hair colour".

Turning our attention to the prominent (and dreadful) recent impacts of flooding in the Somerset Levels. These events took a serious toll on the lives and livelihoods of residents - with particularly arduous circumstances being endured by those members of the farming community based on land that was inundated for the longest periods of time. However, surely we should not fall into a known cognitive trap that makes an easy soundbite - but actually completely ignores the true situation? Aren't we at risk of selling those communities at risk of flooding short by offering purely cosmetic activities?

The sound-bite of "we must dredge the rivers" so that the flood water can be taken away intuitively makes sense - and it has been readily accepted (and campaigned for). But could this be just another version of the Linda problem? Might we be accepting the simple story that we can construct in our own minds instead of taking the tough look at the complex and unpalatable evidence at hand? Consider the following, provable, facts:


  • It would be impossible to dredge the rivers to a capacity that would accommodate the volume of water that flooded such a vast area of land
  • The limited "hydraulic gradient" imposed by the low-lying land (especially at high tide) significantly limits the rate at which water will run out to sea

In other words, it doesn't matter how many lanes you add to a motorway if there is still a road block at the far end...

All of which brings us right back round to Nassim Taleb and his writings on the concept of fragility. You see, Mr. Taleb - far from being an economic boffin with no connection to the real world - actually puts his money where his mouth is. He has amassed a (considerable) income by adopting a particular philosophy as a financial trader. His approach could be summed up in part by the following thought experiment:

It does not matter that you cannot predict which specific lorry (on which specific day) will destroy a weak bridge; it is just important to know that the bridge is fragile.

By identifying those commodities and institutions that are fragile to catastrophic blow-ups, it can be possible to insulate yourself from the negative consequences of such an (inevitable - but unpredictable in time) event. Moreover, it is actually possible to bet against such fragile institutions! This is how Taleb not only survived, but actively profited from the stock market collapse of 1987. He also correctly predicted that the credit crunch (and ongoing associated recession) was an inevitable consequence of the activities of big banking...

So, here is what we know about the significant (but obscure) downsides of trying naively and too aggressively to remove randomness to produce predictable stability within a chaotic system (such as flood water conveyance by channel modification): periods of apparent stability are followed by a catastrophic event of much greater magnitude...

Furthermore, we already realise that it is not really that important to know when a catastrophe will strike. Instead it is important to know whether we are fragile to the effects of that catastrophe when it does strike. Is the bridge strong or weak??

We KNOW that building and living in the floodplain will be, from time to time, fragile to unusually high rainfall, falling on especially impervious and steep surfaces that run into low-lying land where the tides can prevent the escape of that spectacular rainfall. It is not a consequence of insufficient intervention into the size and shape of the river channels - it is an inescapable feature of flood plains. Consequently, no measure (regardless of how expensive) can be put in place that will eliminate this risk and that fragility. However, it is interesting to note that one of the corners of Somerset that did NOT experience catastrophic flooding last summer was the areas in which some of the natural variability of water escaping onto the floodplains had been re-instated...

Dredging upstream of a "roadblock" reduces flood risk?
Linda is more likely to be a feminist bank-teller?


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