This is how the Lancashire Colne-ites keep themselves looking so trim even after the Xmas pud.

Trout in the Town

Also, if you want to join in, watch this Space as well as my blog (above):

Colne Water Angling Club

Paul,

Please explain the current obsession, because that it what it appears to be, with Large Woody Debris (LWD). Everybody, including the EA and Natural England seems to be determined to fill our rivers with the stuff irrespective of the actual need on a site by site basis.

Also, why is it that NE designates a chalk stream as a SSSI on the basis of its typical chalk stream characteristics and then proceeds to change those characteristics by shoving in damn great logs and putting in islands. Neither of these have been chalk stream characteristics since people started putting in mills back in the early Middle Ages - ie about 7-800 years ago.

They seem to think that by doing this they will increase the trout population. There is a stretch of the Lambourn not far from me that has more trout per metre than anywhere else in my part of the country, and there's not a log to be seen!

Its a good way of introducing heterogeneity, producing holding habitat for adult fish (that may otherwise neddy off downstream) as well as sorting/grading spawning gravels.

The logs used in this example (on the Colne) are specifically to protect the toe of the bank which is currently collapsing and dumping tons of silt/sand into spawning areas - so not all LWD is for the same purpose. The coarse brash in this case is used to dampen out fast floodwater flows (rather than hard engineered solutions that would engender very rapid flows and high shear velocities)

WTT import LWD specifically to release particular bottlenecks (e.g. where there is a lack of well-sorted, silt-free gravel) and the simple fact is that most angling clubs remove naturally occurring LWD because they see it as a nuisance.

In almost all natural river systems, LWD and the associated localised scouring are absolutely instrumental in producing point bars and ramps of spawning gravel, generating scour pools and so on (in other words, it helps produce the planform and cross-sectional variation you see in natural streams). It also supports a host of invertebrates the prop up the food chain of trout and grayling as well as providing overhead cover and shelter from predators like goosanders, cormorants, big trout....

Historically man has either removed the natural inputs of LWD (i.e. cut all the trees down for agricultural or development purposes so that none can fall into the river) or we anglers pull it out when it does manage to fall in (because we might lose the odd fly on it).

As you well know Bob - wild brown trout do not like eyeballing each other and are very territorial. If you can break up the boring, uniform spaces in a silty slow-flowing trapezoidal cross-section pool and produce a nice "egg box" lumpy stream bed with a variety of gravel/cobble areas (as well as "screening" the trout from each other's view with big lumps of wood) you will increase the adult and juvenile holding capacity (and promote ranunculus growth to boot).

The difficulty with saying what is "traditional" or historically the case for a particular stream depends on the era that you arbitrarily choose as your benchmark. This benchmark could well be at a time when many practices were being applied to your chosen river that are massively detrimental to the wild salmonid populations (e.g. weir installation, overwidening, dredging and simplification of the channel).

Far better as a fishery manager to look at conditions that are currently outside niche requirements for your fish and then apply sensible tools to bring them back within those requirements. LWD is an excellent way of reintroducing the processes that actually produce trout habitat in unmodified streams - it also breaks down over time.

I guess the current support for (at least not removing) LWD is that it is much closer to what happened before we interfered with our rivers compared to building hard-engineered static and over-designed structures.

With respect to island installation and other issues - this is typically done where the channel has become overwide (either through dredging/other engineering or through cattle poaching). It is one way of producing concentrated flows that can clean gravel and provide the energy to produce localised scour.

As an angler; guess on the bottom picture where this little chap was lying:




Of course, he was underneath the shelter of the fallen tree trunk in the little crease produced by the root ball.

I don't know if Warren still has the photos but there was a uniform section of the Wye that was electrofished for the sum total of 2 fish in about 70 yards of pool. The "post LWD and brash introduction" surveys were giving close to 100 fish (many large fish too) from memory.

---------- Post added at 09:12 AM ---------- Previous post was at 09:05 AM ----------

Re your bit of the Lambourn, presumably those fish have access to well sorted gravel ramps further upstream (whether produced by logs or by clumps of ranunculus?). Similarly, I presume the pools have some structure (ranunculus again?) that breaks up the lines of sight between fish? If not, are they all stockies??

Great reply, Paul.

My main concern is for the chalkstreams near where I live and the obsession, and there is no other word for it, in shoving trees into them without a lot of thought as to the purpose behind such actions. It seems to me and to some of the keepers I know that "it's the thing to do". People need to consider that there is more than one way to part a feline from his fur coat!

The Lambourn stretch that I mentioned is lightly stocked with triploids. Out of the 160 odd fish caught in the last survey less than 10 were stock fish survivors. There is plenty of cover on the non-fishing bank, lots of Ranunculus and plenty of cress along the margins. The substrate is excellent flint gravel and the fish seem to spawn more or less anywhere.

On another part of that same river several years ago we caught over 500 trout from a 100 metre section. 90% of them were juveniles and were caught from extensive cress beds growing in water about 6" deep. As you say, trout don't like each other very much and if you can have the conditions where there is both good gravel and instream cover then there will be lots of trout. I merely wish that people would consider what they are trying to do before they start dropping trees in the river.

A case of where it ain't broke; don't fix it.

From primary scientific research, the effects of manipulating a system that is already "within niche conditions" are very unpredictable and usually not beneficial. Conversely, the effects of restoration are far more predictable when you take something that is outside of niche requirements and bring it within.


On balance, I would say that it is more common for fishery managers/angling clubs to remove good quality natural LWD (and worsen their fishery) than the instances where people want to retain or introduce it where it would be a benefit.