WTT Blog

Stocked fish or native invader?

Posted on August 17, 2017

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.

Tags under trees tell a tale

Posted on August 07, 2017

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.

Habitat to Help Trout and Native Crayfish in a Midlands Brook

Posted on July 26, 2017

I was recently able to use the Trout in the Town project to provide two days of training in habitat work for the Friends of Bilbrook (find them on Facebook here: https://www.facebook.com/Bilbrookfriends/ ).


We used some very simple techniques of woody material introduction and stabilisation to help create submerged "cover" habitat for fish (and hopefully the native crayfish that have been recorded in the brook). Some simple tweaks to those techniques also helped to promote more diverse depth over the cross-section of the brook at selected points.

At the same time as creating localised bedscour - the installed material also encourage patches of sediment deposition. The combination of those actions produce a pattern of separation between areas of fine silt and coarser bed material in a patchwork fashion. In this way, a greater variety of micro-habitats are created and this creates many more opportunities for aquatic species. At the same time, it also creates the variety needed for different critical life-cycle stages within individual species such as trout.

Because the materials for the woody material introduction and stabilisation were...

Low flows and salmonid rivers: an update

Posted on July 14, 2017

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!

Malcolm Greenhalgh's June Blog

Posted on July 11, 2017

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.

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

Posted on June 26, 2017

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. 

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

What makes an apex predator: the ferox trout

Posted on June 05, 2017

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.

Malcolm Greenhalgh's May Blog

Posted on June 02, 2017

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.

Guest Blog from Malcolm Greenhalgh

Posted on May 30, 2017

Malcolm Greenhalgh is one of the WTT's Vice Presidents and we will be featuring occasional blog posts from him. This one is from April:

For the first time since 1965 I have bought a brown trout and coarse fish England & Wales Rod Licence instead of a salmon and migratory trout licence. The reason is that I can no longer spend hours cast-cast-casting because of arthritis in my right forelimb. A few years ago, when the arthritis began to hinder my fishing, I went to the medic’s who sent me for some X-rays. Then I was summoned to the clinic at Wrightington where a specialist in the condition told me, as he perused the X-rays, “As bad a case of RSI as one can come across! What repetitive job have you done that has caused such damage to all these joints?”

The riparian invasion: salmonid friend or foe?

Posted on May 23, 2017

The riparian invasion: salmonid friend or foe?

'Tis the season to bash balsam - if you don't know how to, check out the definitive guide from WTT chum, Theo Pike, for guidance! Timely then for a new blog focussing on invasive plants. Alex Seeney from the Centre for River Ecosystem Science (CRESS) at the University of Stirling, is battling with balsam and knotweed from a more academic angle, and below gives an overview of some his research to date. This valuable work is supported by Scottish Natural Heritage.

Some of the most diverse and complex habitat types in aquatic systems are found at the interface between terrestrial and aquatic communities – the riparian zone. These diverse, dynamic systems provide an ecologically important buffer between land and water, and as such they are of particular importance to the health and quality of the waterways they border.

How Volunteers in Sheffield Make Big River Habitat Projects Successful

Posted on April 28, 2017



You've done a big, ambitious partnership project to deculvert a section of urban stream, but now the civil engineering contractors have gone to their next job. The site is left to mature...what next? Very seldom does this kind of project have any budget for ongoing ecological monitoring (which is a frequent and justified criticism of habitat improvement works - the lack of ecological effect data).

The same can be said for general "husbandry" of the site - whether it be litter or invasive plant control; or even fairly substantial running repairs...

Step in SPRITE (Sheffield Partnership for Rivers in Town Environments) whose site you can check out on http://www.sheffieldsprite.com, the Sheffield Trout in the Town group and a supporting donation of pre-established planted coir products from Salix River and Wetland Ltd. (with their site here: https://www.salixrw.com)

You can see SPRITE talking about their aquatic invertebrate monitoring and see their repair and site care works in action in the embedded video below:


Can watercress farming directly impact fish communities in chalk streams?

Posted on April 27, 2017

Can watercress farming directly impact fish communities in chalk streams?

Asa White gets to call wading around in the Bourne Rivulet work! Our research interests in chalk streams have some parallels. While I am curious as to how a colourless, odourless gas (methane) contributes to the fuelling of their food webs, Asa is trying to understand how an equally invisible chemical is affecting invertebrate and fish life. Here, he outlines his research plans and offers up the experience of electric fishing - read on! 

Watercress is native to the chalk streams of southern England, and has been harvested for millennia. In the early 19th century, the advent of the railway made commercial production viable for the first time. A growing London market supplied by trains (the famous ‘Watercress Line’ being one) led to an explosion in the number of watercress farms throughout the south of England. Historically, watercress was grown in gravel beds irrigated by water diverted from chalk streams, but hygiene concerns now oblige growers to irrigate their beds using fresh water abstracted from boreholes. In both instances, the water used to irrigate the beds is discharged into adjacent chalk streams. 

Starting Work on The River Went in Yorkshire

Posted on April 18, 2017

Although this is the start of what is planned to be a wider project that tackles multiple issues throughout the full length of this heavily-modified river, the first set of works are shaping up really pleasingly. 

Click Picture to Launch on YouTubeAlec and the rest of the YWT team have made impressive progress to organise and deliver the program of works that we designed on just around 1 km of the River Went, on a project supported by the Environment Agency. It was particularly impressive due to a last minute loss of the previous project manager due to a career move. In the video you can see how Alec worked with the WTT to power through the first, steep part of the learning-curve on in-river structural improvements to a heavily-modified river. The main challenges stemmed from the historic realignment of the channel (and general lack of in-stream structure/debris necessary to create vital habitat for different lifecycle stages of fish and other aquatic life). Coupled with the relatively low gradient and fine particulate material/potential associated diffuse-pollution inputs from upstream, this had made the channel very uniform (boring) and also lacking in diverse substrate (bed material). While the...

Little weirs and little fishes

Posted on April 11, 2017

Little weirs and little fishes

Jeroen Tummers has been wrestling with more holistic fish passage solutions during the course of his PhD with Dr Martyn Lucas at Durham University (Martyn gave us a few comments about this project on a previous WTT Blog). But below, we hear from Jeroen himself, about his valuable contribution.  

One of the most important components in restoring impacted river systems, given their linear nature, is to reconnect habitat patches separated by obstacles to free movement. Fishes rely on free access to habitat upstream, and downstream, in a river system to spawn, for feeding, or for finding refuge. Since the presence of these three functional habitat types can change both spatially and temporally, it is important that free access is retained.