WTT Blog Posts

How do chalk stream fish respond to flow and habitat restoration?

At the WTT Annual Get Together earlier this year, I had the pleasure of bumping into a former MSc student of mine, Simon Whitton, who now works at Affinity Water and is collaborating with colleagues at Cranfield University, supervising PhD students of his own; a perfect opportunity for another guest blog or four! Since abstraction and chalk streams have hit the headlines repeatedly and this year especially, we should follow Mickaël's progress with interest (and that of Jess Picken too)....

Chalk streams are highly important ecosystems and are a fundamental component of the landscape in the south and east of England. They are hotspots of ecological diversity and support important fisheries for trout and dace amongst others. However, the water that feeds chalk streams originates from groundwater, which is under increasing pressure from abstraction to supply our expanding urban populations. This conflict puts chalk streams squarely in the sights of environmental regulators and water companies as they try to find the best ways to preserve the ecology and the water supply. Hence, my project is sponsored by Affinity Water, and the Environment Agency, and is a part of Cranfield University’s Industrial Partnership PhD studentship programme.

My research aims to investigate the effect of habitat restoration and flow restoration on fish communities. To do this, I am using a broad set of techniques to monitor hydromorphological change (river habitat change) and biological change with a specific focus on fish communities. My study sites are on the rivers Beane and Mimram.

To put the information gathered from my field studies into context, a set of reference sites on six chalk streams has been chosen: Misbourne, Chess, Gade, Ver, as well as elsewhere on the Mimram and Beane. Data collected previously on the fish community and habitats of these rivers is being used as a baseline against which future change will be assessed.

The ultimate aim is to provide river managers with evidence on the links between fish, river flows and physical habitat. Information on how fish (and particularly coarse species) use habitats, will help us to decide which types of features to bring back into the river (plants, riffles, etc) to encourage colonisation of sites or to sustain fish populations and ensure resilience in the future.

At the moment, we have completed a first cycle of surveys. At Singlers Marsh in Welwyn, the public was amazed to see fish being caught in the stream, from small bullhead up to a nice-sized brown trout.

We have faced some challenges along the way, such as finding one of the rivers chosen for our survey to be dry in its upper reach. Unfortunately, this situation appears to have been all too common this year, as reported elsewhere on the WTTblog (e.g. Long term abstraction and fishery collapse). While I could not say much about the fish community at the time (cows were more prevalent), I could still assess the dry reach for potential habitat features which are likely to ‘re-emerge’ as the flow returns.

From the techniques we have chosen to monitor our sites, some of the most interesting use cameras to capture images from fixed points both above and below water; this will be the focus of another blog in the near futur

Further information about this specific project and about river-related research from my colleagues at Cranfield University can be found on the following websites:



Or please contact me for more information

Mickaël Dubois (Mickael.Dubois@cranfield.ac.uk, @Mickael_bio_be)

Genetics to underpin effective management

As WTT Conservation Officers, we are asked to make assessments on what is good and bad habitat for trout populations based upon visual observation and expert judgement; this is the basis of a typical Advisory Visit Report. If we had the time and resource, we'd look to the fish themselves to tell us! In this latest blog from current researchers, Jess Fordyce from the University of Glasgow Scottish Centre for Ecology and the Natural Environment outlines how an understanding of the genetic diversity within a catchment can inform more efficient management strategies for safe-gaurding trout populations.

The brown trout, Salmo trutta, is an extremely diverse species in terms of behaviour, physiology, genetics and morphology. Brown trout can adopt a range of life-history strategies which include freshwater residency in rivers and/or lakes, or anadromy – the movement from fresh to saltwater and back again (ie sea trout). The diversity of brown trout in terms of genetics and morphology was the focus of my PhD which was funded by an EU project called IBIS (Integrated Aquatic Resource Management Between Ireland, Northern Ireland and Scotland) and the Atlantic Salmon Trust. My study site was the Foyle catchment which is a large dendritic (branching) system with an area of around 4500km2 located in both Ireland and Northern Ireland. This catchment is managed by the Loughs Agency. Like other catchments across Britain and Ireland, sea trout numbers have been sharply declining over the last few decades. Therefore, it is important to understand the genetic population structuring of brown trout (the pattern of genetic variation) and which environmental factors shape such structuring. From this information, it is possible to detect exactly which populations contribute significantly to the production of sea trout and hence provide focused management.

WTT blog sea trout PhD research population geneticsWTT blog PhD research trout genetics population

An anadromous (‘sea’) trout (left) and juvenile resident brown trout (right)

I aimed to address several objectives throughout my PhD, but here I will only discuss two of them. The first of these aims was to determine the spatial scale at which genetic populations could be detected. In other words, do brown trout form genetically different populations between sampling sites >1km apart, >10km apart etc, and which environmental factors could be driving such genetic diversity? The spatial scales I focused on were:

  • Large - comparison of sampling sites between sub-catchments;
  • Medium - comparison of sampling sites between tributaries within sub-catchments and
  • Small - comparison of sampling sites within tributaries.

It is important for management to know at which spatial scale that genetic population structuring occurs to conserve the maximum amount of important genetic variation within each sub-catchment and which environmental variables drive such variation.

PhD blog WTT research

Illustration of spatial scales used to determine population structuring.

With a team of three or four people, we electrofished ~1 km stretches of 28 sampling locations to catch ~60 juvenile brown trout at each sampling location. Those ~1km stretches of river were to ensure the brown trout we sampled represented more than a few families. The trout were then anesthetised and a non-destructive genetic sample (fin clip of adipose fin) from each was placed in ethanol.

Map showing the location of the Foyle catchment and sampling sites. Highlighted in orange for the next aim I will discuss is the River Faughan and the star shows the location of the Rotary Screw Trap.

I then processed the genetic samples at Queens University, Belfast using a suite of 21 microsatellite markers. Each microsatellite marker targets a short-repeated sequence of DNA, from which the genetic variation of each individual brown trout can be compared. Using the genetic variation, I determined the genetic population structuring of brown trout in the Foyle catchment and which environmental variables could be driving this population structuring. I found extensive genetic population structuring which varied with spatial scale and was driven by environmental variables. This work will be published soon I hope so stay tuned for the details.

Electrofishing one of my sampling locations… it wasn’t always this sunny!

To address another aim of my PhD, I used the genetic information gained from the population structuring of brown trout, described above, to determine which tributaries within the River Faughan produce sea trout. The River Faughan is one of the best sea trout producing rivers in the Foyle catchment and determining where exactly the sea trout are being produced is important for effective and efficient management and conservation.

I used a Rotary Screw Trap in the lower reaches of the River Faughan to capture sea trout smolts during their downstream migration to sea in 2014. The RST has a large cone shaped barrel which is turned by the flow of the water. This rotating barrel allows fish to swim in but they are unable to swim back out and are held in a holding tank at the back of the trap. We would then check the trap every day, collecting fin clip samples for genetics from sea trout smolts and releasing all fish to continue their downstream migration. The fin clips from these smolts and archived genetic samples (scales) from sea trout smolts caught in the same trap between 2005 and 2008 were used to determine which tributaries within the River Faughan produce sea trout.

Rotary screw trap in the lower reaches of the River Faughan.

I processed the genetic samples from sea trout smolts using the same suite of microsatellite markers that I used to determine the genetic population structure described above.  In doing so, I could assign individual sea trout to their tributary or population of origin by using the genetic diversity of each population as a genetic ‘baseline’. Each population represents a different tributary, therefore, the genetic variation of each sea trout smolt can then be matched to the tributary with the most similar genetic variation. Hence I could estimate the proportion of the smolts originating from each tributary and identify the most producitve spawning grounds. Again, these data are in the final throes of the publication process so I cannot yet reveal the fine details but will do so in the near future.

In the meantime, if you have any comments or specific questions, please feel free to contact me.

Jess (j.fordyce.1@research.gla.ac.uk or @JessicaRFordyce)


Stocked fish or native invader?

Anyone with an interest in rivers or lakes and the life within them, be it from a conservation, management, or angling perspective (and of course those three are not mutually exclusive) will be aware of invasive non-native species (INNS), the impacts they may cause in certain situations, and the importance of biosecurity. Ecologists with a particular interest in invaders differentiate between non-native (i.e. those species introduced beyond their original distribution range, a pertinent example being pink salmon) and native invaders (referring to species that add to existing or establish new populations within their native range). The artificial stocking of salmonids into waterbodies is one such example of the deliberate introduction of native invaders, to allegedly enhance commercial and recreational fisheries, as well as for conservation purposes in some instances. The evidence accruing as to the benefits of this approach makes interesting reading.

In 2016, Buoro and colleagues used the global-scale introductions of salmon and trout as a robust biological model (i.e. lots of studies with plenty of data to analyse) to investigate the ecological effects of changing intraspecific (within species; e.g. stocking farmed brown trout in to rivers containing wild brown trout populations) and interspecific (between species; e.g. stocking rainbow trout into lakes with Arctic char) diversity. The enormity of the dataset collated from the literature allowed them to look at various levels of organisation which introduces a lot of complexity. However, the take home message was that, overall, introduction of native invaders resulted in stronger ecological effects than those associated with changes in interspecific diversity caused by non-native species.

Sifting through the results revealed that physiological traits (mainly associated with stress response) were most impacted by native invaders, and probably the basis of the initial response of for example, wild brown trout facing introduced farmed brown trout. Furthermore, the study also revealed significant impacts of native invaders on growth and condition, suggesting that there may be evolutionary consequences further down the line. This is aside from the more direct impacts at the genetic level resulting from interbreeding and the introduction of less ‘fit’ genes if diploid (fertile) native invaders are stocked.

Buoro et al highlighted that actually, there is a significant knowledge gap regarding the wider ecological consequences of introduced native salmonids on recipient communities and ecosystems. A paper published this week by Hasegawa and colleagues has taken up that challenge using the introduction of hatchery chum salmon fry on top of the wild masu salmon fry population, as well as their benthic invertebrate prey, and the algal food of those invertebrates.

They assessed the impacts of a single stocking event, the release of 3 million fry into the Mamachi stream, Hokkaido, northern Japan. As was revealed in the previous meta-analysis (above), the foraging efficiency and growth of wild masu salmon fry was reduced following the introduction of the chum salmon fry (the native invader). There was a marked decrease in abundance of various mayfly and caddis species via predation pressure from the fish. This induced an apparent ‘trophic cascade’ across the various links in the food-chain: Lots of fish induced high predation pressure on the invertebrates, reducing their overall number and therefore reducing the grazing pressure on algae at the bottom of the chain. As a consequence, algal biomass increased although the extra nutrients recycled via stocked fish excretion has also been shown to promote algae.

Together, these findings highlight the need to consider the more subtle ways that introduced native organisms like stocked trout and salmon can potentially change the ecology of a waterbody, as well as the more obvious detriment caused to wild populations of salmonids. The Wild Trout Trust always urges caution and consideration when asked about stocking: our position paper and an ever increasing number of case studies from clubs that have ceased stocking are available on our web pages. Click the green links above.

Tags under trees tell a tale

In science, new questions are always arising from serendipitous discoveries. Angus Lothian tells us of some interesting data on fish predation that has come to light as a part of his PhD project at Durham University, assessing trout behaviour at fish passes.

Every year, Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) undertake an upstream migration in autumn. People watch these fish ‘heavy-weights’ leap, or at least attempt to, over barriers after having already completed maybe tens of miles on their journey to and from sea. Such a migration allows the fish to use rich marine feeding areas to grow larger than they might achieve by staying in freshwater, thus increasing their fecundity or egg production for when they return to their natal rivers. But there are trade-offs. The migration between freshwater and saltwater is filled with risk, resulting in large annual mortality affecting fish populations. For example, for my MRes, I studied the emigration of salmon smolts from rivers, and their behaviour strongly reflected predator avoidance tactics.

But closer to home, the year-round, river-resident brown trout – the same species as sea trout – can also exhibit an annual migration.  Similar to their anadromous counterparts (those fish that move from freshwater to saltwater), brown trout also move to areas of increased nutrient abundance within freshwater environments to grow more efficiently which will be different to where they spawn.  Although on a much smaller scale, substantial risks are also faced by river-resident individuals on their potadromous (within river) migrations.

Last autumn at Durham University, we performed a small study monitoring the spawning migration of adult brown trout in a local river. We fitted sixteen fish with radio transmitters which were subsequently tracked for two months, from mid-October to mid-December 2016.  Two remote logging stations were placed approximately 1.5 km apart on the River Deerness, a sub-tributary of the River Wear, with further manual tracking taking place four times a week.  This involved walking along the river bank for a minimum of 5 km with a radio receiver and antenna to precisely locate each individual fish.  Manual tracking meant we could record exactly where each individual fish was in the river, how far they had moved, and in which direction.

The manual tracking also proved to be useful in a different and unexpected manner.  Radio tags actually function better in air than in the water; not something that you generally need to consider when monitoring fish movement!  On one survey, I could not get a strong fix on a tag in the river.  After several minutes of pacing the river bank, I was about to give up, when I turned around and heard a clearer *beep* in my headset.  Using our unidirectional antenna, it did not take me long to find the tag underneath a tree only 5 m from the river edge.  Even more exciting, the tag was actually encapsulated within a heron pellet!

Over the course of the next month, we made several more visits to the same tree, recovering four of our 16 radio tags, along with some PIT (Passive Integrated Transponder) tags that had been inserted into trout parr in 2014 for a different study.  This means that a heron has used this feeding spot for at least two years.  Further, another three radio tags were found downstream; one of which was found in a heron pellet, but the other two were never retrieved due to being lost in a woodpile and in a relatively large pond.  We know that at least 31.3% of our tagged fish were definitely eaten by herons, and potentially up to 43.8% had succumbed to predation within this 2 month period.  Extrapolating this figure implies that a large proportion of the trout population in the Deerness at least, ranging in size from small parr to larger adults, can be removed by an avian fish predator.

Several questions spring to mind: is this one heron with a good fishing spot? Or, are there several predators along the river that enjoy a fishy snack?  As part of a larger study in the upcoming autumn (2017) - the behaviour of parr, adult brown trout and sea trout at a newly constructed fishway - we will also focus some of our efforts on understanding the potential impact of predation on the trout population of the catchment.  Piscivorous birds along the river will be counted during manual tracking exercises, and frequent searches at their known feeding sites for regurgitated tags will be undertaken.

I hope to bring you an update on how things are going later but in the meantime please contact me if you have any questions or comments regarding my project.

Angus Lothian (angus.j.lothian@durham.ac.uk or @AngusJLothian)

Long term abstraction and fishery collapse

Just a couple of weeks ago, I posted the news article entitled ‘Where have the rivers gone?

A typical British summer has since dropped a deluge of rain across much of the countryside, and with it, will wash away any thoughts of droughts and painfully low flows from most people’s minds. It’s exactly the same with flooding:-

Last autumn showed vividly that we are liable to damaging floods as soon as the autumn rainfall becomes excessive. When this happens, it is our habit to complain loudly, but having concentrated on rapid run off and having covered some of the natural floodplains of our rivers with buildings, we should not be surprised if water invades ill-placed houses. Our second national habit is to forget about it once the mess has been cleared up’ said Hay… in 1969! Over half a century later and it is not abundantly clear to me that we have learned very much from previous flooding events.

Half a century of water abstraction in the Great Plains region of the US, and a group of scientists have learned a great deal. In a paper published this week in the Proceedings of the National Academy of Sciences, Perkin and colleagues have revealed that around 350 miles of stream dried up in eastern Colorado, southwestern Nebraska and northwestern Kansas, all related to groundwater being pumped out of the aquifer and mostly to supply irrigation needs. They have used models to forecast from the available long-term data, and their projections are that if no changes are made to the way abstraction of groundwater occurs, then a further 180 miles of streams will disappear.

As a consequence, the fish community is changing. Those fish species that are typically found in larger streams and rivers are being lost, and they are being replaced by other species with characteristic traits that enable them to survive in smaller streams. Barriers such as dams and weirs on the river systems are making the problem worse by isolating populations and preventing exchange or replenishment of species. Taking the Arikaree River as just one example, seven of the sixteen native fish species have disappeared since the groundwater pumping started in earnest.

River Quin, in Hertfordshire: Photo by Charles Rangeley Wilson

Groundwater abstraction occurs all around the globe; for those in the south of the UK, this may sound all too familiar. We do not have a particularly diverse fish assemblage in UK rivers in the first place so we really can’t afford to start losing them in this manner. But of course, it’s not just fish that are affected. All biota in those groundwater fed systems will be affected in some manner. If you have read the blogs by Jess Picken regarding her PhD work on low flow events in chalkstreams and how riverflies are affected, you will have seen hints in her data that flows do not have to be low for very long before there are marked shifts in the invertebrate communities.

This paper by Perkin again highlights the value of collecting and interrogating long-term datasets, and for ensuring that funding is set aside to allow organisations like the Centre for Ecology & Hydrology (CEH)here in the UK to continue to do so. The more detailed time-series data we have, the better we can forecast and predict to inform management and policy for our future rivers, and the ecosystem services they provide for our future generations. 

UPDATE: On 16/08, CEH posted a blog entitled Hydrological situation update, or: whatever happened to the 'drought'? highlighting the fact that 'Drought is a slowly evolving phenomenon – deficits built up over such a long period can take a long period to return to surplus'. Very interesting read.

Low flows and salmonid rivers: an update

Jess Picken was the first to contribute to our new series of guest blogs in which she outlined plans for her PhD. And clearly, she has been busy! She is back with an update already...

To recap on my previous post, numerous studies have reported that low flow reduces the density of salmonids within streams. What is not so well-known is what, or how, other parts of the salmonids’ ecosystem are also affected by low flow. Riverflies and other aquatic macroinvertebrates make up a large proportion of juvenile salmonid diet, which is subsequently reflected in salmonid growth rate, condition and survival. Understanding how the availability of these macroinvertebrates changes with reduced summer flow is important to help conserve fish species of high UK and European importance.

My life at the moment... macroinvertebrates down the microscope!

My experimental study sites are three carrier streams of the River Itchen where complete control of the flow is achieved by sluice gates at the top of each stream. During the summer, the sluice gates were lowered in order to experimentally induce low-flow conditions. Each stream experienced a four-week low-flow treatment, reduced by 90% (Red9), 50% (Red5), or not altered as a control (Cont). Riverfly and macroinvertebrate sampling occurred before (Bef), during (Dur) and after (Aft) each flow treatment (ie following reinstatement of ‘normal’ flow by opening the sluices), and taken to the laboratory for identification. To decipher the results, the codes in parentheses identify each event and where, so for example: Bef*Red9 is a sample taken from the stream before the flow was reduced by 90%

Now... don't panic.... let me walk you through what this plot means!

Picken PhD ordination invertebrate community Itchen

It shows that in the before (Bef*) and (Dur*) samples, macroinvertebrate communities were relatively similar in all flow treatments (Cont/Red9/Red5). We know this because all the Bef* red arrows and all the Dur* red arrows are roughly pointing in the same direction. Black arrows indicate the riverfly and macroinvertebrate species that together make up the whole community.

However, what stands out (to me at least!) is in the after low-flow sampling occasion (Aft*). Aft*Cont is pointing in a markedly different direction to the Aft*Red9 and Aft*Red5. This indicates that following on from re-instatement of normal flow, there was a shift in macroinvertebrate community. Furthermore, the severity of low flow (ie 90% or 50%) treatments are actually remarkably similar. One explanation for this may be that during low-flow, parts of the river bed may become exposed and dry out. Therefore, when flow is reinstated, opportunistic invertebrates may move on to these 'new' patches of stream that would not have become available if low-flow had not occurred. There is one more years’ worth of data to collect and analyse to see if this interesting pattern holds. Watch this space....

Please contact me if you have any questions or comments!

Jessica (j.picken@qmul.ac.uk, or @jesspicken)

Malcolm Greenhalgh's June Blog

In this blog post, WTT Vice President Malcolm Greenhalgh reflects on climate, weather, pollution and sea trout fishing prospects for July. 
Malcolm lives in the north west of England, not dry dustbowl that is the south east !

I am now not only a believer in global climate change, but I am 90% sure that Homo sapiens is probably responsible for the change that has occurred since at least the middle of the 20th century.

During the Industrial Revolution we did alter the climate here in the north of England through the use of coal fires in the Dark Satanic cotton and woollen mills of Lancashire and Yorkshire and in homes and other factories. The effects of the soot laden smoke, with its high acidic nature, resulted in dense smogs in the lowlands and in very acid rainfall in the moorland through to the control of air pollution by Act of Parliament in the 1950s. I once remember cycling home in smog and not being able to see where I was on the road where we lived. I had to get off my bike and walk down the pavement until I recognised our stone gate posts. Visibility was barely five yards. On another occasion I guessed at where I had to turn right in the car and found myself driving up someone’s drive about thirty yards from the avenue into which I wanted to turn right! And in 1969-70, when I was working on the wildlife of the Pennine moorlands that separate Lancashire and Yorkshire, I learned from work done by earlier naturalists in the 19th century that large tracts of Sphagnum bog and its associated special flora, including species like sundew, had been exterminated by the extreme acidity. This loss had resulted in bare peat that had eroded on the flat moorland summits, leading to more violent spates in the rivers fed by these moorland bogs.

Today this sort of pollution is greatly declined and here in northern England conservation organisations are working hard to get the natural moorland flora and its associated bogs back in place. It’s just that the form of pollution has changed and is less visible. And its effects are a general warming-up of the world climates and more extreme weather.

In my book The Ribble, written a decade ago in 2007-2008 and published in 2009, I wrote, of the upper Ribble valley, “In 1969 I was out on the moors on 77 days scattered throughout the year...I experienced snowfall in every month from November to April, and lying snow from November to mid-May.....in 1999 I spent 40 days in the upper dale and saw no sleet or snow falling.” This last winter (2016-7) I recorded snow falling in the head of the Ribble very early morning on the 2nd January, the night of 12th-13th January, on the 9th February (flurries), 28th February but it quickly turned to rain, and on the morning of my 71st birthday, April 25. But in every case it melted within a very few hours. Lying snow is now quite a rare event here in northwest England, causing panic amongst commuters for whom driving in snow is outside their experience.

For extreme weather,  take this June:  we had a heat-wave 17th-21st with perhaps the hottest June day on record, and very heavy rainfall on 5th-7th (with damaging gales), on the 10th and continuously or almost continuously from the 27th to the 30th (it is still raining as I write this on the 30th at 4.53pm).  Outside the heat-wave, my diary records most days having a very cold wind from the NE to NW. Go back to Junes in the 1960s, 1970s and 1980s, these extremes were rarely encountered then.

The consequence is that, throughout the British Isles judging from correspondents, we have had the worst first four months of the trout fishing season since recording began.  
                                               *                                        *                                            *
So much for the bad news; now for the good.

Those of you old enough will remember dear old Hugh Falkus’s two BBC wildlife programmes in the “World About Us” series, Self Portrait of a Happy Man and Salmo the Leaper, made in the 1970s. In those Hugh showed us pools on the Cumberland Esk that held great shoals of sea trout, and through the 1960s and 1970s rivers like the Esk, Lune and Dovey were famed for their vast numbers of sea trout. Then, from about 1980, the number of sea trout declined; I fished the Falkus Esk from 1987-98 and, though I did catch a few sea trout each year there, never saw such big shoals in the pools. This decline was down to a collapse of the Irish Sea herring due to gross overfishing, which was down to the usual EU sea fisheries maladministration. This not only affected the sea trout, but also other fish and sea birds that relied heavily on juvenile herrings (i.e. whitebait) for their food. The Irish Sea cod stocks collapsed (no longer could I go out off the Lancashire coast and catch lots of cod up to the teens and more in weight). And the common tern colonies that I had studies in the late 1960s and 1970s and which then generated well in excess of one young to fledging per pair per summer, a production that resulted in the colonies increasing, collapsed.

In 1981 commercial fishing for herring was banned in the Irish Sea, another case of closing the door after the horse has bolted. That was 36 years ago, and in the many years since the herring population very, very slowly increased so that in the last two or three years it has come close to its 1970s level. Cod stocks are recovering and from cursory observations of one Ribble ternery this spring it seems that their productivity is on the ‘up’.

Likewise the sea trout. The often torrential rains of 5th to 10th June resulted in some good runs of sea trout and the rains that came on the 27th and have only just cleared up (it is 5.30pm on the 30th June and it has just stopped raining) have brought up the rivers again and sea trout will be heading upstream.

Get out there, for July promises to be a belter for sea trout!

Malcolm Greenhalgh

Here’s one I made earlier….The Hoffer Brook

By Rob Mungovan, WTT Conservation Officer for East Anglia and Central Region

As a new starter my colleagues have been interested to know what projects I’ve already delivered whilst working as a local authority ecologist. I’m able to explain all the usual techniques of channel narrowing and bed raising but one novel approach keeps getting more questions. So the clearest way to explain it is to write it down, and include some pictures. The one below hows the restored brook. 

Hoffer brook 1

The restored (or re-built?) brook. The new bed is suspended over soft silt through the use of grass mesh.

The Hoffer Brook is a small degraded chalk stream in Cambridgeshire that runs for approximately 8km. It suffers from very low flows in its upper reaches but lower down it has a permanent flow. I have known the brook all my life as it forms the parish boundary to the village where I grew up, and I can be certain that there were no trout in it from the late 1980s through to recent years. The reason for the lack of trout was a combination of factors but the main bottleneck seems to have been the almost entire lack of spawning substrate and subsequent fry and parr habitat  - these are the shallow streamy bits which are in stark contrast to the deep slow moving features that the brook exhibits. Water quality of the brook was considered to be high.

The Beds, Cambs and Northants Wildlife Trust, and specifically their Water for Wildlife Officer Ruth Hawksley, have been crucial partners in the delivery of this project. The Wildlife Trust was able to secure funding and oversee the contractual arrangements, while I worked-up the detailed spec and made sure that the final delivery was correct on the ground.

Having played and swum in the brook on many occasions it had always been known that some sections were pretty treacherous and appeared to have no natural bottom or hard bed. This was investigated by a topographical survey and sure enough there were areas that were significantly over-deep. But was this really the work of past over-dredging?

“Not entirely” is the conclusion that I have since come to. Whilst historic dredging may have over-deepened much of the brook, the local topography appeared to be showing a pattern to the deeper sections. What I believed we had encountered was the edge of the chalk escarpment running down to the lower ground. If the land had sunk and sea levels risen what I think we’d found were some areas of ancient silted shallow valleys. There was also another explanation to throw in, that of pingo ponds. This part of Cambridgeshire has a number of post-glacial groundwater-fed ponds still in existence. These ponds formed where an up-welling of ground water froze to form ice lenses which then over thousands of years of freeze and thaw, resulted in round ponds scattered across the landscape. The brook appears to have linked some of these ancient ponds.

Hofffer brook 2

A “bottomless” part of the brook, note the top of the ranging pole. This part is now ~0.5m deep. 

So in terms of restoration, what were we really restoring? The truthful answer is that no-one exactly knows how the brook was more the fifty years ago. Old enclosure maps showed that some of the meanders were being straightened way back. But the hardest, and probably most damaging works came in the mid-1970s when the brook was dug deep and some residents recall it being a mess that simply never recovered to its former state. Older residents of Foxton say how the brook was more open, had a shallow gravelly bed in many places, had a swift flow, and a range of fish species could be seen including brown trout (and to my knowledge they were not stocked). So the usual techniques of channel narrowing, brushwood ledge creation and bed raising all seemed appropriate but how much gravel would be needed? A huge amount. An amount that would have been prohibitively expensive. A new approach was therefore needed.

I’d been thinking this one through for years. I’d toyed with the idea of lining the bed so that the silt could actually become an aid to the project. But how, and with what materials?

One idea had been to use wooden trellises cut down to shape to form a support lattice over the silt. It is known that once wood is in anaerobic silt it hardly degrades but how would we have kept the trellis from tipping as material was placed on it, and what if gaps had formed between the trellis? That could be very dangerous and we could have lost the gravel.

Through brainstorming, Ruth and I (plus my Dad I’ll admit) came up with the approach of using vehicle tracking mesh (Grassform’s grass mesh, light duty) the type that is stretched out over soft ground. The advantage of using the mesh was that it could be cut to the correct width and then be stretched out for a full 30m length (the rolls of mesh came in 2m x 30m lengths).

Hoffer brook 3        Hoffer brook 4









Threading the rope through the mesh to support it.                                 Sinking the mesh, supported by rope from posts.


hoffer brook 5                  hoffer brook 6









The mesh is flexible so a vegetated margin can be retained as found


Hoffer brook 7               Hoffer brook 8









Note the springs arising from the bed. If a woven mesh was used the natural upwelling could have been interfered with.

Further benefits of the grass mesh were that is could be fixed together using numerous cable ties to make a strong and fail safe join. Then the matting could have 8mm polypropylene rope threaded through the mesh. These lengths of rope were then tied to 100mm chestnut posts that had been driven into the bank at 1m intervals. This effectively allowed the mesh and rope combination to be supported on top of the silt providing a strong but slightly adaptable support onto which we could then re-create a chalk stream. See photos above.

This idea came from those times where you are hitting away at posts only for them to suddenly push through a hard layer to move rapidly into a softer layer. I can envisage times where during the land forming processes of the last ice age there must have been episodes of meltwater which would have moved huge quantities of coarse material and distributed them randomly across the floodplain. In subsequent millennia our rivers have been acting to sort and move this material. I was simply trying to re-create one of the gravel lenses that rests on the softer valley mires.

On to this supporting layer we were able to undertake the usual approach of re-building a small chalk stream. Obviously, we had to take more care when placing the material initially; we couldn’t simply start at one end, we had to layer it all so that the whole mesh was tensioned equally. This was particularly important where we had tried to cut the mesh to accommodate a meander. I will admit that even today the mesh at one point still flexes up.

We did all of this based on sound judgement and a little bit of managed risk taking. We only did the first 45m using this method and were then able to use a more conventional approach, Ideally, I’d have liked to have got more depth of gravel down (we did get ~0.5m in places) but we were restricted by the proximity of a  railway line and its overhead wires; consequently we didn’t get the upper reaches as elevated as we ideally would have. And we never knew how much weight the chestnut posts would support before being pulled out of the soft ground (we were confident of the load-bearing capacity of the rope and mesh).

Hoffer brook 9

Work completed. Note that this photo location is the same point as where the 2m ranging pole had previously been pushed entirely into the soft bed. 


But most importantly we have been able to restore/re-create a chalk stream habitat where once a spring-fed ditch had run for at least a generation. We’ve now got brown trout, minnow and brook lamprey spawning and attractive beds of water crowfoot and starwort.

To date the work has held up absolutely fine. It has experienced some of the wettest weather in recent times where the open mesh would have had no problem in allowing natural springs to rise from the bed again (which can be a problem where tightly woven membranes are used as liners), the chestnut stakes are still in place (even though some were hit by my old drainage team during their flail cutting operations which took out a couple of pieces of rope). And the new brook looks perfect.

Hoffer brook restored

Photo taken about 14 months after completion. 
The water crowfoot was planted as there was none upstream to colonise this area.


Lessons learned:

1.       The use of Grassform’s grass mesh to support aggregate over deep silt can work on small watercourses.

2.       It is not necessary to desilt a channel before undertaking such work (I had instructed a partial desilt simply to remove the dense Phragmites reed growth but the presence of deep silt can be looked upon as an indicator of where the new bed should perhaps be).

3.       Use rope of 8mm thickness or upwards (due to a shortage of materials we did use some finer rope and it did look stretched but has not broken).

4.       The placement of the supporting posts should be a close as can be afforded (this is important as if one support fails there will be others to take the load).

5.       Instead of leaving the chestnut posts slightly proud (where one would have thought a drainage operative would have noticed them!), it would be better to cut them off flush at ground level and then to cover them over with 100mm of soil. That way the posts would have been entirely protected from mechanical destruction, the risk of interference by people and/or degradation by environmental factors.

6.       This approach is not suitable where future watercourse maintenance may necessitate the use of an excavator (this work could be destroyed very easily by one dig and pull of a bucket).

7.       I have no first-hand experience to say if this approach could withstand high velocity flood flows but then you don’t usually get high velocity scouring flows where very deep silt has accumulated for decades. But my gut feeling is probably “yes” as the gravel is effectively protecting the mesh beneath it and as long as the gravel is not lifted then the structure beneath should be fine.

8.       For a greater degree of confidence in the durability of this type of approach some form of metal support post could be used such as a universal beam. A universal beam could be drilled through to create an anchor point for polypropylene rope or even steel cable (we’d decided against scaffold poles as they were too narrow in diameter and were likely to be pulled over when ground conditions became soft).

What makes an apex predator: the ferox trout

I have to admit, the topic of this research really floats my boat (as you may have noticed from the latest Salmo Science Spot)…. I spent several years trying to convince people that perched at the top of the Loch Ness food web was not an elusive plesiosaur but something much, much more sexy. Ferox! So I’m really pleased that the newly doctored Martin Hughes has taken time out to precis his completed PhD, but it does mean I’ll have to review the WTT ferox pages with his new findings.

The brown trout, Salmo trutta, is an incredibly diverse species. Individuals from the same population can adopt completely different life history strategies, which are often given vernacular names. For example, some S. trutta remain in small freshwater streams their entire lives; these are referred to as resident trout. Others migrate into large rivers or lakes to complete their life cycle and retain the name brown trout, but some that migrate into estuarine waters are referred to as slob trout and others that fully migrate into marine waters before returning to natal streams to spawn are called sea trout. One relatively understudied life history is that of ferox trout. ‘Ferox’ which is Latin for ‘Fierce’ is aptly used for these large piscivorous trout which can grow to large size (14kg UK record) and are exceptionally long lived (23 years oldest UK record- reports of 39 years old in Norway). Their impressive growth potential and life span combined with their rarity and near mythical status only adds to the allure to both anglers and scientists alike.

Astonishingly, even in the 21st century we know relatively little about these incredible fish. Genetic studies throughout the 1980s in Ireland only added to the mystery surrounding ferox trout. Pioneering research by Andy Ferguson and his colleagues at Queens University Belfast found some populations of ferox trout were actually part of an ancient lineage of trout, believed to be one of the original lineages that invaded the British Isles after the glaciers retreated approximately 12,000 years ago. This raised interesting questions surrounding the evolutionary history of ferox trout and their taxonomic classification. In 2008, ferox trout were reclassified as Salmo ferox which was recognised by the IUCN. The IUCN however classified Salmo ferox on the Red List of Threatened Species under the category of ‘Data Deficient’ meaning the risk of extinction of ferox trout could not be assessed due to a lack of scientific data. In other words, these potentially vulnerable and genetically distinct fish are not afforded any sort of protection!

I was first introduced to ferox trout during my undergraduate degree at the University of Glasgow and after a meeting with the enthusiastic Alistair Thorne at the Marine Scotland Faskally Laboratory, I was hooked. I based my undergraduate dissertation on ferox trout and working alongside another ferox trout legend, Alan Kettle-White from the Argyll Fisheries Trust (and WTT Trustee), I collected data on ferox trout and brown trout from Loch Awe.

Hughes ferox wild trout trust blog awe

A mirror still Loch Awe in the summer of 2011 (just think of the midges…)

My undergraduate research led directly into a postgraduate degree which was funded by a large EU project called ‘Integrated Aquatic Resource Management Between Ireland, Northern Ireland and Scotland’ or IBIS (http://www.loughs-agency.org/ibis-projects/). As an IBIS PhD student, I was tasked with conducting investigatory research into ferox trout which would inform the scientific community, fishery managers and policy makers. I designed my research to help inform stakeholders on the geographic distribution of ferox trout, gain a greater understanding of their basic underlying biology (including physiology and behaviour), and also investigate differences between brown trout and ferox trout co-habiting the same lake.

Hughes ferox wild trout trust blog

The IBIS project partners the Loughs Agency, Queens University Belfast and Glasgow Univeristy, funded by the European Union.

My first research project on ferox trout distribution was based on an extensive literature review and analysis of angling books going back hundreds of years. After almost 2 years of research, I found 192 lakes in Scotland have evidence of supporting a ferox trout population. I also investigated the environmental characteristics associated with these ferox trout populations and found a strong correlation between lake size, lake depth, and the presence of Arctic charr Salvelinus alpinus.  The strong relationship between ferox trout, habitat size (lake size and depth) and prey species (Arctic charr) are indicative of most apex predator populations. This research was published in the Journal of Fish biology in 2015 and tells us two main things:

  1. Ferox trout populations are relatively rare given the amount of lakes in Scotland they could be found in, and
  2. Ferox trout, where they do exist are most likely fulfilling the role of an apex predator. Given the disproportionate importance that apex predators play in ecosystems globally, ferox trout are likely to be providing an essential ecological service in those lakes.

The main focus of my research was to investigate underlying biological differences between ferox trout and brown trout. Traditionally this is done using an experimental design called a ‘common garden experiment’. Common garden experiments, as the name suggests, are often used with plants, where plants are raised in a common environment (same temperature, same light exposure, same water availability etc.) so any observed differences between plants are inherited differences and not differences caused by the environment. Essentially you are controlling the external environment at all times. The same can be done for animals raised from birth. However, the logistics and animal husbandry involved makes such an experiment much more complex, and combined with the rarity of ferox trout populations, this was a monumental task. In fact, there were no published records of anyone having collected eggs from spawning ferox trout.

I began my quest for ferox trout eggs in October 2013, in the Highlands around Loch Maree, with the help of Peter Cunningham of the Wester Ross Fisheries Trust. During the following weeks of sampling numerous rivers in the Loch Maree catchment, we caught lots of brown trout but not a single ferox. It turned out to be one of the mildest Octobers on record and the rivers were extremely low. It looked like we might miss our opportunity to catch any spawning ferox trout for another year which would change the planned research considerably.

We identified the river most likely to support spawning ferox trout and waited for the rains to arrive. In early November, the first substantial overnight rainfall was forecast and we assembled a team to be on the river first thing in the morning. Within 2 hours we had captured 3 female ferox trout and a number of males, including a huge male fish which looked like he’d been through the wars, and won! We quickly transported the fish to nearby holding tanks before spawning them to create full sibling groups and hybrid crosses between ferox trout and brown trout.

There is a critical ‘water hardening’ period after fertilisation in which eggs cannot be moved after a 48-hour period or they perish as they become sensitive to movement and light. The water temperature of the eggs also had to be kept cooler than 8 degrees centigrade at all times or I'd risk losing the clutches. After successful fertilisation I stored the precious cargo in flasks surrounded by ice and water in a small blue ford van. With the windows down and AC on I left Wester Ross at 9pm and drove down to the Scottish Centre for Ecology and the Natural Environment (SCENE) on Loch Lomond, wearing two scarfs, a thermal hat and a pair of gloves, wincing at every bump in the road. I arrived at the field station about 3am and began to carefully transport the eggs into specialised temperature-controlled fridges. After an hour of careful negotiation, the final clutch was placed into the temperature control unit.

hughes ferox wild trout trust blog

Ferox trout eggs at a crucial stage of development, the ‘eyed’ stage.

For three months I visited the lab to check the eggs (including Christmas day!) and was ecstatic (relieved) to find they had survived the journey and the embryos were developing well. On the 5th of January 2014, most of the eggs began to hatch and for first time we had juvenile ferox trout in a common garden experiment. Now the real work could begin.

Over the following year all fish were held at the same water temperature and fed the same amount of food allowing me to measure differences in yolk sac size, head shape morphology, metabolism, lipid deposition and mortality rate.

hughes ferox alevins wild trout trust blog

3 day old hatchlings known as alevins. The ferox trout had much larger yolks sacs which is unsurprising as larger females produce larger eggs with larger yolk sacs. What is important, however, is the larger the yolk sac the higher the rate of survival.

Perhaps one of the most interesting experiments we conducted was investigating the dominance behaviour between juvenile brown trout and ferox trout. As juvenile trout form dominance hierarchies in natal streams, with the most dominant individuals enjoying better feeding opportunities, we postulated ferox trout would be more dominant than brown trout. Our reasoning behind this hypothesis was in order to feed on other fish, ferox trout must reach a large size quickly. It is therefore more important for a juvenile ferox trout to reach a large size by acquiring more food than it is for a juvenile brown trout. Our results were staggering! Ferox trout were more dominant than brown trout in 90% of the trials.

hughes ferox

Photograph of fish behaviour footage. On the left is a submissive brown trout juvenile and on the right a light-coloured, dominant ferox juvenile.

Given we had controlled environmental effects and controlled the size of each individual (each fish was matched to within 2mm length of one another), this behaviour is likely inherited from ferox parents. If this behaviour is replicated in the wild, it suggests that juvenile ferox trout may be predetermined to become large piscivorous trout, which supports the evidence provided by Ferguson that ferox trout may be distinct from other brown trout.

The results from the other physiological experiments will be published later this year and therefore cannot be discussed ahead of time. However, more interesting distinctions have been discovered. Like all good research, I have more questions than I started off with and I would like to thank all who have been involved in the research and continue to support the project. If you would like to find out more information, please like the ‘The Ferox Project’ FaceBook page where I will continue to update the progress of the research, follow me on Twitter @DrMartinHughes and watch the full behaviour video behaviour video here (https://www.youtube.com/watch?v=hHBIqHyIe0s&feature=youtu.be)

Martin Hughes (m.hughes.4@research.gla.ac.uk)


Related publications

Hughes, M.R., Dodd, J.A., Maitland, P.S. and Adams, C.E., 2016. Lake bathymetry and species occurrence predict the distribution of a lacustrine apex predator. Journal of fish biology.

Hughes, M.R., Van Leeuwen, T.E., Cunningham, P.D. and Adams, C.E., 2016. Parentally acquired differences in resource acquisition ability between brown trout from alternative life history parentage. Ecology of Freshwater Fish.

Malcolm Greenhalgh's May Blog

Malcolm Greenhalgh is a WTT Vice President and contributes the occasional blog post. Here are his thoughts from the end of May. 

At the Wild Trout Trust’s weekend in Derbyshire, of which more anon, everyone from the four corners of our island agreed that this was the coldest spring, and worst spring, for trout fishing that they could recall. Up to the last fortnight May, like the end of March and April, the weather was dominated by strong winds from a direction veering from north-west to east-north-east. As my old friend and mentor that late Jack Norris used to say, “The flies won’t hatch in numbers and the trout won’t rise properly in a wind like this. A cold downstream wind is the kiss of death for dry fly fishing!” (see my little book The Floating Fly for more of dear old Jack). So I saved petrol instead of wasting it by not driving miles to the rivers other than a couple of visits when the weather was not too bad, including an afternoon on the Hodder during the summery heat wave that brought spring, and May, to an end.

The good news is that reports indicate that our rivers have good heads of wild brown trout and grayling. Mick Addison for instance, told me of a visit to the Eden where trout were feeding everywhere on the minutest “little black things” but that he couldn’t catch them even on a size 22 dry fly. Similarly Chris Hosker and Keith Owen visited a lovely beat of the Wharfe on the cold 6th May and found fish everywhere, some of them nice and large, and they caught a few on their nymphs. It was the same on the middle Ribble and upper Hodder.

Incidentally, Chris and Keith stopped off on their way to the Wharfe at Gargrave to support Bradford City AA’s fund raising event for the Wild Trout Trust, who have done some magnificent habitat work on the Aire following the Environmental Agency’s idiotic habitat mismanagement.

            *                 *                *

I am now going to speak to the converted, for nitwits don’t read anything, it seems.

I don’t kill wild brown trout, despite the fact that I like to eat trout. Instead I eat top quality rainbow trout, usually by hot smoking them over cherry and hickory and making a pate by whizzing their lovely meat with lemon juice and crème fraiche in the blender. My favourite haunt is Frank Casson’s Barnsfold Water, for the two lakes making up the fishery have great buzzer hatches and the trout raised by Frank and his son Richard are as good to eat as any.

I arrived on the 25th and, having said ‘Hello!’, went to a favourite spot where food accumulates and the trout rise to eat it. Three others were fishing further along the bank and six others scattered elsewhere on the bank of this lake. As I tackled up I noticed that trout were rising.

The leader I use here is 16-feet in length and has two droppers so that I can fish a ‘washing line’ of three flies, each of which matches one of three common foods. Because there was a nice south-westerly breeze, which might bring lots of landbred insects onto the water, I tied my Foam Beetle (size 14) to the top dropper. A fortnight earlier all the trout came to that, and when I came to clean the brace I took home an autopsy revealed lots of tiny black beetles in their stomachs.  Middle dropper was a black Suspender Buzzer (14), one of the greatest inventions of the late John Goddard that matches a midge pupa hanging down from the surface film prior to the adult stage emerging . And on the point I knotted a size 16 black Cul de Canard Midge.

First cast a trout took the CDC Midge, a lovely fat trout with perfect fins and weighing about three pounds. That went in the bag. I cut off the soggy successful fly and knotted on a fresh CDC Midge. I made the second cast of the day and a trout took immediately, again a lovely fish not quite as large as the first. It too went into my bag. The next cast also caught a fish (three in three casts!) as did another about ten minutes later. With finger, wrist and elbow joints giving me pain it was time to stop: playing Frank’s trout really does hurt!

One of the trio fishing further along the bank came over as I discombooberated my tackle.

“What did you get them on?”

“A size 16 CDC dry fly.”

“Never heard of it.” I showed him the four that were drying in my tweed hat. 

“You never caught them on them little flies!” I took the two trout from my bag and spooned them, revealing stomachs nearly packed with tiny black flies and beetles.

“I didn’t think big trout would eat such little things. We thought they would like big things like this.” He showed me a box of reservoir ‘lures’.

“I fish a washing line of three small flies...”

He interrupted: “A what?”

I write magazine articles and have written a few books on flies and fly fishing. Why don’t people read them? Of course, they use the internet. Google ‘Buzzer’ and see the confusing mass of patterns, ideas, ‘rigs’ on offer. But it’s simple: in all real fly fishing you just match what the fish are eating where, in the water, the fish are feeding.

                       *                             *                             *

A special plea. I am primarily a fly fisherman for wild trout and grayling and there are two organisations whose drive is for the protection of these two beautiful species, the Wild Trout Trust and the Grayling Society. I feel privileged to be a vice president of the first and trustee of the second. In spring the WTT has its conference weekend and in autumn the Grayling Soc has theirs. Both are wonderful events, with the Sundays giving members opportunity to fish some of the greatest rivers in Britain. On the Saturdays the presentations are always fascinating and I learn much from them.

But not enough folk who also enjoy fishing for wild trout and grayling are members. They...you (if you are not)...ought to be members, for the rivers and lakes, and the wild trout and grayling that they....you (if you are not)...enjoy, they need your support.



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