Ellie’s Weir…ed Blog

In this post our GIS whizz Ellie Spilsbury outlines some of the work we have been doing to identify ways to improve the sustainability of the fisheries in our rivers and hopefully aid the return of salmon for the first time since the Industrial Revolution.

*Look closely and you will see hundreds of Minnows collecting at the bottom of this weir, unable to ascend. See the area in the water that looks dark brown; they are Minnows.*

Visit each of the three sections for more detail:

A familiar Story

Data analysis with a Salmon Splash of professional opinion

(Tr)outcomes expected

A familar story

Once upon a time, our River Aire had the highest Salmon population of any Yorkshire river. Then came the Industrial Revolution, which saw the wool and fabric industry boom throughout Yorkshire. Mills were constructed accompanied by weirs to harness our river’s energy. Although the mills are now closed and are becoming swanky new flats, the weirs often remain, isolating ecosystems that lie between them. Weirs disrupt the natural transport of sediment downstream, causing a build-up of silt and gravel behind the weir, which is detrimental to the habitat of spawning fish. Since 2011, one of the Aire River Trust’s goals has been to increase the connectivity of our river and its tributaries by removing or re-configuring weirs to allow fish passage. Following earlier work to install fish passes through and downstream of Leeds, significant steps towards this goal were made in 2022 with the successful construction of four fish passes as part of the DNAire project.

When we see water flowing over weirs, creating the sounds of waterfalls and visually pleasing white waters, it is easy to forget their man-made heritage and artificiality. It is hard to imagine seeing through the eyes of a migrating trout or salmon; every cell in its body instinctively directing it upstream to spawn, using both the stars and the earth’s magnetic field for navigation and then facing an unpassable wall of Yorkshire-dressed stone. It is often not just the height of the weir that presents the issue but the combination of weir height and the shallow depth of the concrete sill below the weir. The height at which salmon and trout jump is directly affected by the relative depth of the water at the foot of the barrier and the “hydraulic jump,” which boosts their leap.

The Environment Agency (EA) has identified around four hundred river obstacles within the Aire Catchment. However, we believe there to be many more. For example, the EA recorded two barriers to fish passage on Pitty Beck, yet on our Bradford Becks Walkovers, we found 11. This pattern is most likely repeated on each beck. Currently, tackling the removal of every weir in the catchment is unattainable. So, how did we prioritise them into a workable top twenty?

Data analysis with a Salmon splash of professional opinion

With help from The Rivers Trust, we are the first regional rivers trust to code an ArcGIS tool to accurately calculate the length of a river (including tributaries and forks) that would be opened and re-connected by the removal of every mapped weir in the Aire Catchment. Alongside this, we analysed ecological assessment data, invertebrate biodiversity, local community data (including deprivation), and weir visibility to the public. We assigned a score to each outcome and designed a weighted decision-making matrix that identified the weirs that scored the most highly. The data only tells us half the story, so we took our results to our expert team and discussed those weirs for which a solution in the short(ish) term might be feasible.

Once we had twenty feasible weirs, it was time to ground truth our ideas. The purpose of site visits is to add or, more often, diminish our confidence in the feasibility of the weir so that we only carry the most achievable sites to the next stage. We evaluated the weirs’ condition, site access, utility services or abstraction points, and landowner engagement by photographing and recording the area, our thoughts, and encounters.

The most surprising discovery for me was the actual size of a weir. After months of viewing photographs without visual perspective, weirs can appear to be half the scale of the real-life structure. Take a moment to analyse this photo: how tall do you believe it to be? See the very bottom of the blog for the upside-down answer.

(Tr)outcomes

We are fast approaching the end of the site visits and write-up stage. It is time to narrow our shortlist of twenty weirs down to four. So, it will be back around the table for our professionals to decide on the four “leak” proof projects to invest in. These four weirs will be subject to a comprehensive feasibility study and design process. I hope my next blog post will include more designs, machinery, hard hats and re-naturalised rivers.

TROUT

The Wild Trout Trust contributes to several Aire Rivers Trust projects and initiatives, such as the Better Becks programme. It helps that Prof Jonny Grey, the WTT Research & Conservation Officer, is an Airedale resident and has a good working knowledge of his local system. One of his projects (TROUT), independent from ART but with similar aspirations and goals as the Better Becks project, is producing some very encouraging data.

TROUT – or Tackling Resilience on Underperforming Tributaries – is a 5-year project funded under the Yorkshire Water Biodiversity Enhancement programme. It aims to do what it says on the tin by improving habitat both instream and within the riparian zone and boosting trout fry numbers as a result. The WTT use brown trout as a sentinel species – if there is a healthy, wild, sustainable population of trout in a stream or river, it suggests that there is sufficient water of sufficient quality flowing through a mosaic of sufficient quality habitat to fulfil the various requirements of the trout life-cycle. And being in the middle of the food chain, lots of trout suggests plenty of food (mostly riverine and land-based invertebrates such as mayflies, shrimp & worms) and also plenty of food for predators of trout (otter & heron etc).

*Young of year trout fry ~70mm in length*

What form might habitat improvement take? Because I have been focussing mostly on headwater tributaries to boost spawning, it generally involves methods to sort and keep gravel free from silt so the trout can lay eggs and they’ll incubate safely. Adding wood, wiggling channels, providing cover and shade, and preventing fine sediment from washing in are all important, as is ensuring adult fish have free access in and out!

TROUT involves 3 sites in each of the Aire, Nidd & Wharfe catchments and I measure success against a number of control becks. I will focus on the Aire outcomes here, but it’s useful to place these in the wider context of other Dales rivers – see my summary of the overall project on the WTT pages, here.

One site is the goit in Hirst Woods at Seven-Arches and it is slightly atypical to the other sites in the project in that the focus is for ‘coarse’ species rather than trout per se. I posted a blog about early developments last year, here. In a nutshell, the work resulted in a doubling in the species count and increased the abundance of fish from 10s to 1000s! Build it and they will come…..

Haw Beck flows between Embsay and Skipton behind the Skipton Quarry and from there into Eller Beck. Tarmac Ltd and another local landowner have allowed us to exclude livestock, plant trees, introduce wood and generally diversify the habitat, as well as remove a redundant low-head weir. Indeed, ART volunteers helped me with the trees. In 2 years, we have boosted the trout fry numbers by 10x.

*Pinning woody deflectors into the upper reaches of Haw Beck*

The third site, Flasby Beck, flows into Eshton Beck and ultimately into the Aire below Gargrave. It just needed a good dose of wood, big wood, to kick the channel about a bit and provide refugia. So it wasn’t terrible, to begin with, but it was underperforming! There are now 6x the number of trout fry able to reside at the site.

*Volunteers measuring trout fry next to a deposition bar created by introduced wood still visible in the bankside herbage*

Relatively simple interventions give rise to big wins over a relatively short time frame. TROUT runs for 2 more years and I will be monitoring until the end to see if those population boosts are sustainable. More information is available, here.

Electrofishing in Hirst Woods

A guest blog by Prof Jon Grey from the Wild Trout Trust.

Back in May, the new footbridges constructed by Aire Rivers Trust in Hirst Woods over the old mill goit made an immediate and obvious impact on the walkers, both two and four-footed. But they were also built to reduce the human impact in the goit itself. Over the past months and with input from the Wild Trout Trust, members of Saltaire AC have been working steadily towards reinstating the flow and reintroducing some habitat features to benefit the flora and fauna of the goit.

This has involved the removal and relocation of accumulated boulders and freeing up the compacted sediments in between to allow fresh water to flow through the goit even under summer conditions. The water bubbling over the riffles (shallow gravelly stretches) provides a very different habitat to the slower deeper stretches which remain quite silty on the bed.

Volunteers from Saltaire Angling Club installing brush mattresses

It is hoped that with some higher flows over winter, much of the silt that accumulated when the goit was blocked up will be flushed out or relocated to the sides where we have installed some ‘brash mattresses’. These are densely packed branches and twigs tucked behind chestnut posts on the inside of bends to accentuate the sinuosity of the channel (make it more wiggly) and create dead zones into which the silt will percolate and eventually stabilise the material. As the woody material breaks down over time, marginal plants should colonise and further stabilise the structure.

Brash mattresses also provide excellent nursery habitat for young fish with plenty of protection from both flood flow and predators. More physical diversity in the channel allows for more biological diversity too.

The impacts on fish are much harder to ‘see’. However, part of the funding for the habitat-focussed project from the Yorkshire Water Biodiversity Enhancement Fund was ring-fenced for monitoring pre and post works. On Friday 19^th Sept, we electric-fished the full goit in exactly the same manner as we did last year prior to any improvements.

Last year from the relatively stagnant water of the blocked goit, we caught very few fish (~60) from only three species: three-spined stickleback, stone loach, and minnow. The stickleback is characteristic of slow or stagnant waters and the stone loach favours a more silty bed. Hence, the impoverished fish community reflected the sorry state of the goit then.

This year, we caught six species, adding chub, bullhead, and gudgeon to the list. All of these ‘new’ species favour more flow, especially the bullhead that was typically found around the new riffles on the cleaner gravel and cobble. Furthermore, the goit was teeming with fish this year. We did not bother to net minnow after the first 10m and I would estimate we would have had several thousand if we had continued. The small chub (~100mm) and fry of all the other species indicated that the goit was once more offering suitable nursery habitat.

The results speak for themselves. Good news. No wonder the local kingfishers have been far more frequent visitors of late! I’m excited to see what further changes will bring to the goit in 2022.

Prof Jonny Grey (Wild Trout Trust)

Electrofishing with Saltaire Angling Association and the Aire Rivers Trust in September 2021

The Electronic Aire

Brown trout after being tagged below Newlay weir

Lockdown. Restriction. Isolation. Are a few of the many words used to describe 2020. However, these words may also be used to refer to our river systems and the challenges faced by many of the fish populations that reside within them. Whilst many of us were house bound in 2020, construction of four fish passes to help reconnect habitats for river resident and migratory fish species in the River Aire commenced. Here I hope to give you all an insight into how I tagging fish by implanting electronic tags allows us to find out what is going on beneath the water surface, and what difference these fish passes are having on the lives of our fish.

The effect of weirs on wildlife

Barriers such as weirs and dams disrupt fish migration routes, fragment fish populations, and are a major contributing factor to the extinction of fish species globally. In 2020, a scientific paper (Belletti et al., 2020) highlighted how there are over 1 million barriers that fragment European rivers, with an estimated 48,293 barriers in UK waterways, each restricting or halting the movements of native fishes in some form.

The River Aire has 34 major weirs situated along its 114-km length that are barriers to resident and migratory fish. Fish passage solutions (fish passes) have been installed on many of these weirs to help improve movements of fish along the River Aire. The DNAire project is constructing fish passes on another four weirs (Armley, Newlay, Kirkstall & Saltaire), with the major aim of enabling upstream migrating adult Atlantic salmon to reach spawning grounds at Skipton.

These fish passes do not just open up migration routes for the iconic salmon, they will hopefully provide passage routes for river-resident coarse and salmonid fish species too.

How efficient are fish passes?

In conjunction with the DNAire project, the University of Hull International Fisheries Institute (HIFI) together with the Environment Agency are investigating the movements of fish in the Aire.

One of the key aims of this investigation is to assess the efficiency of the DNAire fish passes at Newlay and Saltaire weirs. To achieve this aim, HIFI have spent the last three years capturing and tagging fish (brown trout, barbel, roach and chub) between Armley and Hirst Mill. In addition, efforts are being made to capture and tag Atlantic salmon in the lower Aire that will hopefully migrate upstream and pass through the DNAire fish passes. Passive Integrated Transponder (PIT) tags, similar to those put in cats and dogs, enable us to identify individual tagged fish.

These tags do not have a battery – and thus last the life of the fish – and emit a unique ID when activated by an electromagnetic antennas installed inside the fish passes. The antennas are strategically located to detect when fish approach, enter and ascend each fish pass. With this data, we can calculate the fish pass performance as well as provide additional information on environmental conditions when particular species move through the catchment.

Saltaire fish pass during construction. The baffles in the Larinier fish pass (left) can be seen with PIT antennas mounted on wooden beams across them. The plastic eel pass can also be seen (right).

Building knowledge for the future

Investigating fish pass performance and factors influencing passage is key to understanding effectiveness of fish passes constructed during the DNAire project and for developing future fish passes. We are all working towards a more natural and healthy River Aire that both fish and society can benefit from. We will continue to collect data in the coming months and will hopefully share results with you in a future blog.

Find out more about the work of the Hull International Fisheries Institute Here >

Salmon Safari

Open Aireways