WTT Blog Posts

Start 'em young

There has been much ‘Twittering’ of late as various organisations across the UK are venturing into classrooms to engage with children via aquatic beasties, and particularly our totemic species - the brown trout.

WTT chums at the Clyde River Foundation (CRF) coordinate #Clydeintheclassroom. It’s a huge venture, working with some 90 classes to engage with >2000 kids this year alone. It’s also very much a hands-on project, using aspects of the trout life history to promote awareness of river ecology, to engage with nature, and to help young people across the River Clyde catchment develop a sense of pride in their local environment. Furthermore, it provides a great basis for outdoor learning and STEM education.

Clyde River Foundation classroom education outreach enegagement science trout

On a recent visit to chat with Willie Yeomans, Catchment Manager at CRF, I learned that through the project, they have engaged with over 20,000 children at almost 400 schools. Check out the info-graphic above; that's some reach! Willie is keen to point out that on the Clyde, the trout are not used as part of a stocking project but purely as an educational tool; they’ve used triploids for a number of years now.

I’ve also been chatting with Gareth Jones, Catchment Science Coordinator for Ribble Life Together at Ribble Rivers Trust. Within the Ribble catchment and currently only in primary schools, they operate #troutintheclassroom with similar aims to those of Clyde RF. At Ribble, they are building upon the trout life-cycle by adding a variety of new activities from angling development / coaching, invertebrate monitoring, mayfly in the classroom, demonstration tables for river form and functioning, to poetry and musical events. Check out some of the enthusiastic school blog posts available on Burnley’s Urban River Enhancement Site.

In my day, things like this were definitely 'extra-curricular'! Excellent ventures I'm sure you'll agree, and they are not the only ones, just two I have personally come across recently. If you are a Twitter user, try the #hashtags mentioned above to see the kids (and trout) in action!

WTT has for a long time offered a similar educational project - Mayfly in the classroom – with free, downloadable resources on the WTT website, here.


Sediment sources and salmonid successes

Village pond weir dam sediment

On my WTT-inspired ramblings recently, I came across a shocking sight, above. Shocking because firstly, I was expecting to see a village pond complete with a raft of local ducks bobbing around, not a barren mudscape stuck behind a defunct dam; and secondly, because I immediately started to wonder where all that accrued sediment was being washed away to….. and where it was being deposited… and might it not be being dumped upon some salmonid redds at a rather inopportune time?

Sear sediment source salmonid embryo alevin

And a couple of days later, I was alerted to this. The image above depicts the graphical abstract of a recently published research paper by Professor David Sear, a key figure on the WTT Scientific Advisory Panel. While fine sediments are known to be a cause of embryo mortality in benthic spawning fish species such as brown trout, most research to date has focussed on the quantity accumulating around eggs, rather than any 'quality' issues associated with particular sediments.

For instance, some sediments will be mostly mineral, while others will contain a proportion of organic matter; it is the latter component which could be particularly detrimental to salmonid (and other species') embryos because of the potential for microbial breakdown of that organic matter, thereby reducing oxygen concentrations available to the eggs.

David and his colleagues exposed the embryos of two salmonids, brown trout and Atlantic salmon, to different sediment loads from different sources. Importantly, source as well as mass of sediment affected spawning habitat quality. While brown trout were less sensitive to sediment impacts compared to salmon, both were markedly affected by sediments derived from sewage treatment works; even the results from damaged road verges was worrying.

The organic content was the key driver determining the impact of a sediment source. Moreover, the effects were still apparent in surviving alevin via reductions in mass, length and yolk sack mass relative to experimental controls, so the overall fitness of the progeny that make it through the egg stage is still compromised. Any detrimental impacts at the vulnerable alevin stage is likely to lead to population consequences later on.

This important research highlights the inadequacy of current metrics and sediment targets which are based on quantity of sediment of a given size, or total daily maximum loads, on the assumption that all fine sediments will have an equal impact upon aquatic ecology. It thus provides resource managers with the evidence to support the development of sediment screening techniques, enabling them to target particular sediment source control strategies in the landscape. Critically, these strategies must encompass the characteristics of the mobilised sediment delivered to waterbodies from specific sources and not just the proportion of different sources of fine sediment.

Being in a relatively upland location with little improved land surrounding it, and situated in a small village, I am hoping that the pond sediments I found are of low organic content. Plus, recent snow melt has hopefully flushed it rapidly through the system so it has not had time to settle on any favourable spawning gravels. Hopefully!

For access to the research paper, click here, and for further recent information on land use and soil impacts on rivers, click here to be taken to a WTT news item from last year.

Reflecting on all this rain

Lothersdale farm fields

This is the view from my office window. Of late, I have been lucky to see across the valley. When it has been sufficiently clear there has been a stark message staring me in the face. So, what’s wrong in this image? OK, it’s not a great image but then it was taken in blowing rain. The field (centre shot) has a similar slope / exposure as those surrounding it yet it is the only one veined with rivulets of water. It is also the only one under permanent livestock grazing as compared to the fields on either side through which stock is rotated regularly. The result is a reduced crop plant height, root structure (and probably diversity), and more compacted soils leading to serious (visible) overland flow during times of heavy rain. At the bottom of that field is a tributary of the River Aire; little wonder that the Aire is often occupying the full width of its floodplain (below).

Aire flood


Everyone and their dog has had a view on the recent flooding in Cumbria and Lancashire, and not surprisingly these views tend to polarise; those driven by raw emotion as personal possessions and property are lost or destroyed, versus more objective analyses based upon long-term data records. Inevitably there are some commentators calling for the construction of more and better flood defences whilst there are those advocating more upstream thinking and rewilding of the upper catchments to slow the flow by intercepting rainfall and buffering impacts downstream.

Let’s face it, we have to contend with a long historical legacy of denuding the catchment of natural vegetation and in particular trees, as well as the development of village to city scale infrastructure upon floodplains with vast areas of impermeable surface and many pinch-points on watercourses like bridges and culverts. It is difficult to envisage the scale of defences that would be required to withstand the unprecedented rainfall at the beginning of December (1 in 1300 year; CEH site). Certainly, the aesthetic amenity and access values of having a babbling brook flowing through a village, or river gliding through a town centre, i.e. reasons that those very sites were originally settled, would be lost completely. It is also estimated (from models, because obviously there are no empirical data available) that 100% reforestation of the upper catchment would be unlikely to completely prevent such a scale of flooding when the water reached more urbanised / less natural infrastructure in the lowlands.

For a very measured consideration of the role trees may play in soaking up excess rainwater, read this contribution to The Conversation. I say measured, the message is positive from tree planting programmes such as the Pontbren Project, which followers of WTT will have heard us talk about on numerous occasions. However, providing robust and replicated scientific evidence along the lines of 'X trees planted here saves Y households over there from flooding following Z rainfall' is difficult.

There are clear evidence-based benefits to be derived from an integrated approach involving the whole catchment (summarised in the UK National Ecosystem Assessment Technical Report, here). And there are tantalising glimmers of potential uptake of such measures with the Environment Secretary announcing the investigation of upstream options for slowing key rivers amidst the Cumbrian Floods Partnership goals, calls for increasing the existing target of 11 million trees planted by 2020 to be upped to 200 million (via Confor), and established projects for ‘slowing the flow’ such as that in the Vale of Pickering reported in the recent Environment Agency blog ‘Creating a better place’. There is clearly no point in simply ploughing money into flood defences at the lower end of the catchment and expecting them to withstand the brunt of the water conveyed there by a depauperate system upstream, a point raised again and again by George Monbiot, and plain for all to see, unfortunately, in Keswick and Carlisle.

The key is integration and that includes depolarising the ‘camps’ currently at loggerheads, such as the ‘rewilding’ versus farming contingent. There are undoubtedly opportunities for more extensive areas of woodland (re)generation in the uplands, but not to the detriment of farmers, who are in essence the cultural element that is critical to the survival of communities in such rural areas. Hence, upstream options need to be (carefully) put into place to complement any (hopefully) sensitive ‘softer’ engineering within our urban environments such as SUDS – Sustainable Urban Drainage Systems. I say softer engineering in the hope that the dredging debate does not rear its ugly head again. Constraining water to an overly deep channel and conveying it downstream as quickly as possible costs millions, requires costly upkeep, is typically reactive, and rarely works as recent events show; and the environmental costs are always high (see the WTT view on dredging).

There is no panacea, but by thinking holistically to embrace and fortify natural ecosystem resilience to extreme events, perhaps we can move away from the oft repeated rhetoric of flood defence.

Small land use changes reap big freshwater benefits

The UK landscape is a mosaic primarily of agriculture interspersed with woodland, grassland, urban enclaves and veined with river networks and wetlands. We should all realise by now that this pattern in the landscape has a marked effect on 'ecosystem goods and services', the natural benefits that the environment provides to us, and particularly those associated with freshwater. How we use (or abuse) the land, i.e. influence the landscape pattern, and the downstream consequences to water quality are a focus of the current consultation on diffuse pollution to which WTT has already responded (and I encourage you to do so too).    

A new study of an urbanising but predominantly agricultural landscape in the US draws upon data from 100 Wisconsin sub-watersheds and has important implications for managing and restoring landscapes to enhance surface water quality, groundwater quality, and groundwater supply. The study considered the landscape pattern in terms of composition (the type and amount of particular patches) and its configuration (the layout of those patches); and while both appear to have some bearing upon freshwater services, the composition had a stronger influence on water quality and supply. 

river Aire, erosion, buffer strip, land use, managementIn other words, tweaking the relative size of some of those patches in the pattern could bring about considerable benefits to freshwaters. This is especially important when considering that large-scale changes to the landscape will rarely happen. One of the small tweaks with a disproportionate benefit would be to increase the size of wetlands and buffer strips within the landscape, native vegetation placed between cropland and lakes and rivers, with the multiple benefits of providing shade, bank-stability, litter and shelter, whilst taking up nutrients and trapping soils (reducing erosion) from the land. To many recipients of WTT Advisory Visits, this should sound very familiar! Compare and contrast the river banks in the image here: on the far bank there is a fence and (narrow) buffer strip; on the near bank, there is no protection and the erosion is evident. A picture paints a thousand words, but do we necessarily take heed?

In essence, the study above is landscape scale support for some of the very small scale mitigation measures advocated, for example, by my colleagues at the Lancaster Environment Centre (and in collaboration with the Game & Wildlife Conservation Trust). In a report card for the European Commission, they summarise some of their published findings on how small artificial wetlands created in the corners of agricultural land can prevent soil loss and recapture agricultural by-products, thereby reducing pollution of nearby watercourses. Simple, but oh so effective. WTT Conservation Officers spent a very interesting day at the site of this work, Loddington in Leicestershire, earlier in the year.


Making Connections

Man-made barriers, obstacles, call them what you will, are commonplace along our waterways as we have (typically) in the past tried to harness or control the flow of water for our own use. Some of these installations were incredibly insensitive to the local and more widely spread ecology and physical processes in rivers and streams, not just the fish that might want free passage both up and downstream at all life stages, and in all seasons.Swanside Beck, low cost baffle, weir, Ribble Rivers Trust, connectivity

I recently spent an afternoon with Mike Forty, a PhD student registered at Durham University, and based with the Ribble Rivers Trust. His work, using telemetry to assess the efficiency with which fish can pass obstacles, has been enlightening, and some of the statistics he can rattle off are mind-boggling. His work was featured in the presentation that Jack Spees (Director of RRT) gave at our recent WTT Gathering and captured on video here. For example, the low cost baffle system that was installed on a previously almost impassable weir on Swanside Beck (picture to right) can now be ascended in 23 seconds (according to one sea trout), and several resident brown trout have been up and down it numerous times!

Canal & Rivers Trust, weir, connectivity, Eshton BeckAnother of these low-cost baffle systems is being installed on Eshton Beck. Kevin Sunderland (Aire Rivers Trust) has been a driving force for connectivity issues with weirs, not only here, but throughout the Aire catchment. The Canal & Rivers Trust are undertaking the work in consultation with the local Environment Agency and I went along with Pete Turner to see them in action (pic to left). The design was drafted so that the gauging component of the weir would not be affected by any changes in flow over the crest.

This structure is ~0.5km upstream of the confluence with the R Aire, and by my reckoning after a swift glance at a map, should open up ~15km of potential stream network. This could be particularly important for trout and other fish from the Aire that are severely limited in spawning habitat within the mainstem channel. I wonder if Bradford City Angling Association catch returns will demonstrate and noticeable increase in smaller size classes of trout over the next few seasons?

Check out the new app which will hopefully allow the public at large to contribute to identifying and prioritising river obstacles wherever they may be.

Pre works assessment for Eastburn Beck

Eastburn Beck is a tributary of the River Aire in Yorkshire. It is typical of a northern freestone stream / river that has had a chequered history with industrialisation, and as a consequence, it has lost some of its vitality to the constraints of walled banks and a host of weirs. The walls keep long sectioEastburn Beck stream river weir conectivityns straightened and have allowed housing to develop on what would have been a far more sinuous, meandering floodplain. The weirs interrupt the natural progression of pool-riffle sequences and have choked the supply of gravels downstream.

The result is a series of impounded shallow sections with uniform depth, flow, and substrate on the bed, and little in the way of cover within stream. While some of the overly wide, shallow sections with plenty of jutting stones creating small pockets of turbulence provide excellent habitat for juvenile trout (and is also favoured by the local pair of dippers), there is a distinct lack of spawning, fry and adult holding habitat.

Trout can be observed in the impounded sections, but that’s not really good news as it is likely that they can also be easily picked off by predators such as heron, goosanders and mink. There is simply very little habitat structure to provide refuge.

As part of a funding bid with Pete Turner (Environment Agency, and driving force behind the Upper Aire Project which recently won the Large Project Category in the WTT Conservation Awards), and in close collaboration with Don Vine (Yorkshire Wildlife Trust), I have put together a proposal to ‘rewild’ some of Eastburn Beck. This is following up on some valuable pilot work by Kevin Sunderland (Aire Rivers Trust) to address connectivity issues. The aim is to improve the habitat for invertebrate and fish communities alike - and by improve, we mean we want to diversify the habitat and make it into a richer mosaic of habitat types which will cater for all life stages of bugs and fish.. This will involve exploiting some of the weaknesses in tEastburn Beck EA Environment Agency electrofishing trouthe redundant weirs and then letting the coming winter spates do some reorganisation of the gravels into hopefully a more natural channel form (yet still within the confines of the walls). Then we will assess what further augmentation is required.  

But how can we measure the success (or not) of our venture? Before we do anything in river, it is important to collect some background and reference data. Essentially, we are conforming to a Before After Control Impact (BACI) experimental design. Sampling before and after any remedial work at the impact sites can be compared to samples before and after at unaffected reference (control) sites; we would expect negligible or little change at the control sites and hopefully some measurable positive changes at the impact sites!

So, to get the ball rolling, Pete organised colleagues from the Environment Agency Yorkshire & NoEnvironment Agency trout survey Eastburn Beckrth East fisheries team to electrofish 50m sections of Eastburn Beck and conduct a preliminary River Habitat Survey for those same sections. A more detailed report will be forthcoming but the population of trout was lower than might be expected, and the size distribution heavily skewed towards smaller individuals, as one might predict from the current habitat available. A few bullhead were also evident.  

The next step is to initiate some riverfly monitoring and to hopefully engage with the local community who seem very passionate about the beck where it flows alongside Lyndhurst Wood near Glusburn. Keep tabs on the development of our project here.

It’s not the length that matters….

Does river habitat restoration have to be a certain scale before it can be considered beneficial to the wider ecology of a river? It’s a question in one form or other that our WTT Conservation Officers often get asked. Is it really worth putting that one log deflector or hinged willow etc into that reach? Without the time or resource to conduct a robust scientific study, we’re often simply basing our opinions upon experience of what has seemed to work before. Despite the increasing number of river restoration projects being initiated across the world, scientific evidence on the long-term impacts of such projects and what makes them a success or a failure is still quite thin on the ground.

Well, apparently it is worth doing at the small scale according to some new research, provided that quality and diversity of habitat are accounted for.

As part of a large project involving sites across 10 different regions of Northern Europe, a research team has studied the effects of two restoration projects in each region: one on a short section of river and one on a longer section. At each restored section, the team not only sampled habitat composition in the river, but interestingly also its floodplain. To complement this, they sampled aquatic plants, insects and fish, as well as floodplain vegetation and ground beetles, and the food web composition and any land–water interactions across the boundary between the two.  These findings were then compared to samples taken upstream at non-restored sections of river of roughly equal length.

After accounting for potential variations in river size and restoration approaches across the different regions, the team found that the length of the actual restoration made no significant difference to its apparent ecological health and the diversity of life within.  The most important driver was the substrate composition of the river bed, i.e. the aquatic habitat it provides for organisms. So, exactly the sort of measures that WTT advise on and instigate to rehabilitate river habitat such as increasing the presence of wood (e.g. tree kickers or hinged willows) to diversify water flows and depths and sort gravels, were found to be responsible for increased populations of fish, aquatic insects, aquatic plants and floodplain vegetation.

Perhaps one of the most interesting findings was the marked effects that were felt beyond the boundary of the river and into the actual floodplain. In-river restorations tend to improve the linkage between the water and the land by creating habitat types close to the river bank, such as bars of deposited gravel and sand, which are often absent in degraded sites. These are readily colonised by floodplain plants and animals which have good dispersal ability.

The study (available here) provides further scientific evidence underpinning some of the holistic restoration work that WTT does to improve habitats, not only for trout, but for all flora and fauna living in and along our river corridors.

Workshop on developing river monitoring for citizen scientists

On behalf of WTT, I recently attended a workshop coordinated by Dr Murray Thompson (a former MSc student of mine), the aim of which was to brainstorm on how to extend and develop river monitoring of restoration projects, particularly for citizen scientists. The workshop was generously supported by Ross Brawn, a good friend and supporter of WTT. The discussions were wide ranging and there were some interesting viewpoints raised by the various contributors (from the Environment Agency, Wildlife Trusts and Rivers Trusts, academia, consultancies, the River Restoration Centre etc).

Why? Well, in the limited number of cases where monitoring (to determine whether the restoration has achieved what it set out to do) is actually considered, then the cost of that monitoring typically is a part of an already limited restoration budget. Funding before and after sample collection, particularly in the longer-term, is not always available. However, the lack of coordinated standardised restoration monitoring has led to a paucity of knowledge about the effectiveness of restoration projects. Where monitoring has been undertaken, the sampling methodologies used were often originally conceived to detect pollution but may be incompatible for detecting ecological recovery. 

How? Coordinated, standardised before-after-control-impact (BACI) monitoring and data collation will mean restorations can be compared within and across catchments. This will help to:

  • inform and refine the design process;
  • demonstrate the success and importance of restoration; and
  • secure restoration funding in the future.

In addition, by simply counting the number of active volunteers using a protocol, it is possible to gauge the societal impact of restoration projects which is often critical information when applying for future funding. 

Murray introduced a device that he has been trialling with an MSc student that can detect an ecological restoration signal which has previously proved elusive. The information is an advance on the Riverfly Partnership RMI data, it is quantitative and there are multiple indicators bound up in one methodology - density and diversity of invertebrates combined with ecosystem functioning: microbial and invertebrate mediated decomposition rates. The approach is still relatively simple and could thus be applied by citizen scientists.

We were mindful that volunteer monitoring cannot replace professional or academic monitoring - which is still essential to develop a causal understanding of successful ecological restoration - but rather could provide more widespread and more frequent complementary data than perhaps could be undertaken by professionals or academics. Where possible, it should be an aim to partner academic and volunteer based monitoring so each informs the other and to integrate data from multiple sources (e.g. data from the EA inc. water quality, invertebrate and fish populations, FreshWater Watch, Urban River Survey, RMI) so there is no duplication of effort. The workshop was great for establishing how this might work best with some interesting ideas about how eDNA could be used, for instance, and how data are shared by the Rivers Trusts already and how this might develop.

A next step that was discussed would be to embellish the method that Murray has developed with some simple measures of geomorphological change, train several catchment hubs on how to apply the protocol, and trial it to refine a citizen science-based approach. A draft protocol based on the workshop discussions and existing methods (e.g. PRAGMO, Urban River Survey) is being drawn up to ensure the approach will capture key variables associated with restoration that also relate to the ecological variables measured. It will be important to establish, for instance, how local efforts contribute to the catchment restoration plan and how catchment processes (or stressors, e.g. poor water quality) affect local restoration projects.

Updates on this initiative will follow.

On another sentinel species

crayfish conference habitat river restoration invasive species

The first National Crayfish Conference to be organized in five years was held at Giggleswick School, almost on my doorstep. As I have supervised three PhD, and countless MSc and BSc student projects on invasive crayfish species during my 10 years at Queen Mary University of London, it seemed sensible to attend. I was granted time to do so on the WTT’s behalf since white clawed crayfish, the species we consider indigenous, and brown trout can both be considered flagship or sentinel species; that is their abundance / population health can tell us something about the quality of the ecosystem in which they reside. There are also other parallels of course, more of which below.

The meeting was arranged over several days to allow plenty of time for networking and a choice of site visits. The location, a plum candidate for Hogwarts, and the logistics organized by PBA Applied Ecology, were first class. The attendees comprised renowned academics and a good smattering of (hopefully) the next generation of young researchers, research institutions, consultants, charities, practitioners, and stakeholders. The time was broadly split in half; the first part focusing upon white clawed crayfish (continuing) issues, and the second, particularly on the invasive species.

Playing Devil’s advocate, I got the distinct feeling that despite the 40+ years of experience accrued since signal crayfish became established in the UK, there is still too parochial a focus on the impacts of the invader upon the indigenous species in X or Y river. There was also scant evidence of habitat restoration / rehabilitation to promote existing populations of the white clawed crayfish which are clearly affected by pressures other than invasive crayfish. One could draw analogies to trout easily here, as the habitat degradation pressures are exactly the same. Indeed, one could draw similarities in native-invasive crayfish interaction to wild-stocked trout interaction. Don’t get me wrong, ark sites and breeding programmes are important in the face of the crayfish plague, but we shouldn’t forget about doing our best for the populations out there that might be clinging on in sub-optimal, headwater retreats.

Focussing more on the invaders, there was good ‘in silico’ modelling work presented that demonstrated the efficacy of trapping in combination with targeted poisoning and mechanical male sterilization. Such models are beginning to pin-point the weak spots to exploit in signal crayfish population dynamics. There was also some interesting experimental mesocosm work on signal crayfish predation of salmonid redds and fry. Under the simplified experimental conditions, crayfish were able to capture and damage a small proportion of the fry. Such research only highlights the importance of juvenile refugia habitat near to the spawning sites.

However, I think we are in grave danger of being 'signal-centric'. Whether it was a reflection of the current distribution of invasive species, perhaps in conjunction with the northerly setting of the conference, or not (and maybe I am biased by my previous research), but I feel the regulators and policy makers have to wake up to those invasive species waiting in the wings.

Scientifically sound and robust data from at least three different universities demonstrated, using different techniques or looking at different attributes / impacts, that there are ‘worse’ invaders than signals already established in the UK: virile and red swamp crayfish (and one might consider mitten crabs here too) are the clear contenders to the crown. Virile and red swamp crayfish (and a close relative of the latter, the White River crayfish) have a very limited distribution at present (as did signals back in the day and now look where we are!); they should be nipped in the bud asap as they appear more voracious, are highly fecund, can cause worse erosion and bioturbation, can outcompete signals, and oh yes, can still carry the plague around.

Despite the despair in the air around many of the presentations, especially with regard to (not) managing the ‘idiot with a bucket’ scenario, the meeting was an absolute success in getting the blue skies researchers, the applied people on the ground, and some of the regulators in the same room and talking. I, for one, hope it is not another five years until the next meeting.

Diet interactions of brown trout and perch at Malham Tarn

It is believed that brown trout and perch were introduced into Malham Tarn by the Cistercian monks in the 12th century. Further stocking of brown trout for recreational fishing started around 1860, continuing off and on until 1994 when the National Trust pushed for a more natural brown trout fishery. Indeed stocking ceased in 2001 and, since 2002, a strict catch and release policy for all fish has been in place.

A few years ago, Jon Payne, now working for one of the fisheries teams at the Environment Agency, looked at the life history and growth rates of brown trout in Malham Tarn and showed very rapid growth compared to other European populations. OK, it’s a limestone lake so the underlying nutrient base for productivity is good, but the elevation and location might suggest pretty harsh growing conditions for fish.

In a new project led by a Masters student, Tim Eldridge from University College London, we are trying to determine how diet might play a role in their incredible growth rate and whether choice of food and interactions with other fish, notably perch, changed with fish size. For example, we might expect that there is a shift from feeding predominantly on invertebrates and zooplankton to piscivory, or even cannibalism, once the fish attain a certain size. To help answer these questions, we are using stable isotope analysis (SIA), a natural chemical tracer of diet retained from within fish scales (removed so the fish can be returned unharmed). This technique relies on the fact that all nitrogen and carbon making up a fish derives from the food that it eats.brown trout, malham tarn, growth, diet, stable isotopes, perch

Sampling (using rod & line, electrofishing, and fyke netting; all under licence) is now complete and we have length & weight data from 700 fish (all safely returned) and with a sub-sample of scale samples from representative size classes. The ages and growth rates are being estimated from scalimetry (like counting the growth rings on tree). The most recent years of growth are now being separated (fiddly under the microscope) for SIA.

We should be able to ‘map’ the food web of Malham Tarn and plot perch and brown trout within that map to determine their trophic position (their place in the food web). We will also be able to determine whether diet switches occur as the fish get older / bigger, and hence if there are different feeding strategies within the population. We will also be able to determine how energy routes through the Malham Tarn food web and estimate the niche size of the fish species present.

Updates on this project work will follow.

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