Promising results so far for LIFE

The Natural Resources Wales (NRW) Four Rivers for LIFE project aims to improve the habitat structure and function of four SAC Rivers; Teifi, Tywi, Cleddau and Usk.

Two years since its launch and to celebrate World Water Day on 22 March, the project wanted to share some encouraging results.   

In this blog, Four Rivers for LIFE Monitoring Officer Sophie Gott explains the importance of continuous monitoring for the project and how the results so far are signalling the positive impact the work is having on river ecosystems.

We have undertaken a lot of baseline monitoring throughout the project, all tailored to the specific restoration interventions and the target species.

For example, River Habitat Survey (RHS) to monitor physical changes to the riverine habitat where we have reintroduced wood or boulders to a river; or electric fishing surveys where we have installed a fish pass.

This baseline monitoring gives us a good idea of what the site is like before we do any work, such as how many fish are there, what the bank structure is like and the make-up of the riverbed substrate.

We can then compare this data to data collected post-interventions, and use this to demonstrate the impact and effectiveness of the work.

We are now at the stage where we are doing post-intervention monitoring at some of our sites, it’s still early days with more analyses of data needed, but we’re seeing some promising results.

Cleddau River work

We’ve reintroduced boulders to one of our river restoration sites on the Cleddau River (you can read more about this work here), where they had previously been dredged out.

Image: Boulders introduced in the Cleddau River (NRW).

At this site we have monitored the fish populations, aquatic plants and river habitat. 

The fish data have been particularly impressive, as shown in the graph below, with big increases in the number of brown trout at the site, and more modest increases in salmon and bullhead numbers. 

Image: Graph shows big increases in the number of brown trout on the Cleddau River (NRW).

The boulders provide local areas of scour, cleaning gravels and increasing the variety of substrate and flow types. This improves the habitat for fish and invertebrates, providing shelter and feeding and spawning areas.

Usk River work

On the River Senni (which is a tributary of the River Usk), Powys County Council with support from the Four Rivers for LIFE Project replaced an old pipe bridge with a clear span bridge (more information here). The old bridge was prone to blocking and too small for the river.

 

Image Left: Electric fishing surveys taking place upstream of the old bridge on the Senni River (NRW).

Image Right: Upstream of the new clear span bridge on the Senni River (NRW).

We have carried out electric fishing surveys at sites upstream of the bridge, and have seen a big increase in the number of juvenile salmon in the river after the works, see graph below.

Image: Graph shows big increase in the number of juvenile salmon in the Senni river (NRW).

Whilst this is only the first year of post works monitoring at these two sites, we are cautiously optimistic that these data show our river restoration work is doing what it was intended to do, helping fish populations to thrive.

New fish tagging programme

It is important to maintain a flexible approach to monitoring, especially when it comes to new or novel techniques.

2024 saw us start a programme of tagging shad on the River Usk with tiny acoustic tags, which we can detect with receivers deployed in the river. 

Tagging shad is a relatively new technique, successfully carried out by the Unlocking the Severn project for the first time in the UK in 2017.

Image: shad 

Although NRW routinely tag salmon smolts on the Usk and smolts and lamprey on the River Dee, we have never tagged shad before. So 2024 was a chance to trial the techniques and see what worked, and what tweaks would be needed to give us the data we needed.

Shad are not able to jump or negotiate very fast water speeds, and the bridge footings at Llanfoist bridge are known to impede their migration, particularly at low flows, and the bridge footing at Crickhowell bridge are impassable.

We hoped to better understand the extent of the shad migration on the River Usk and their behaviour at barriers like Llanfoist and Crickhowell bridges by tracking tagged fish.

We successfully tagged 40 shad at our site downstream of Usk Town. Receivers were deployed at 11 sites from Isca in the tidal reaches, to upstream of Crickhowell Bridge (see map below for location of receivers and tagging station).

Shad were detected at just four of these stations, all in the lower reaches with only one fish reaching as far upstream as Trostrey gauging weir.

Image: Map shows location of shad receivers and tagging stations (NRW).

We are pleased with the success of the tagging methods, all fish were returned safely and 39 left the river post spawning, giving a 97.5% escapement to sea rate.

We gained some valuable data on fish movements in the lower river, however, we did not get sufficient data to determine the impact of the bridge footings - none of our tagged shad made it that far up the river.

Learning lessons to improve our work

On the back of this lack of data relating to the bridges, we are now looking at what changes we can make to our methods to help us get more relevant data.

Firstly, we need to be patient! It is possible that the shad may show a different migratory pattern on their return in 2025 and 2026 – tag batteries last for about 3 years.

Secondly, we know from egg surveys that some shad spawned just downstream of Llanfoist in 2024, but they also spawned in large numbers in the lower reaches of the river, from Usk downstream.

By moving our tagging station upstream of Trostrey, we can catch those shad which are more inclined to migrate further, and with luck, target some of those intent on migrating up to and possibly past Llanfoist.

We also plan to increase the number of fish tagged to 60, and the number of receivers in river.

Finally, one key aspect of monitoring is talking to others who are doing similar work. We have worked closely with Swansea University, who are carrying out shad tagging in the Tywi and Wye, to share knowledge, skills and data.

Their receiver array in the Severn Estuary is providing us with an insight into the behaviour of our Usk shad at sea, where they migrate, how long they spend in the estuary etc. And our work can contribute to their growing dataset on the shad population of the whole Severn Estuary and associated rivers.

Looking forward

We have a few interventions planned that we are still gathering baseline data for in 2025, including fish passage works on the Cleddau, and a large scale river restoration at Cors Caron on the Teifi, as well as continuing the shad and smolt tracking work on the Usk.

We will also continue to carry out post intervention monitoring, gathering the data and evidence to show the positive impact of our schemes so far.

To keep up to date with our work you can follow us on as Facebook, X (formerly Twitter) and Instagram or subscribe to our newsletter here