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)