WTT Blog Posts

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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