The Fish Pass, Byron’s pool

Background:

Byron’s Pool is situated on the South-West of Cambridge, where Trumpington becomes Granchester. The reserve is mostly woodland and is adjacent to the river and the now Trumpington Meadow Country Park. The fish pass creation was part of a wider project which seeked to enhance and develop the reserve in preparation for increased visitor pressure due to the building of 1200 new homes in the near by vicinity.

Therefore, as well as habitat enhancement, the ease of access and visitor experience was considered. This entailed; improving footpaths, more picnic benches, bins, interpretation and notice boards, a new bridge, installation of fishing and canoe platforms and resurfacing of the car park.

In this next section however it is the habitat enhancement that will be concentrated on in more detail.

The project:

Two aspects of habitat enhancement were focused on in this project, firstly the woodland environment and secondly the aquatic.

In the woodland selected trees were felled, this was to reduce shading around the 4 woodland ponds and bank sides of the river. But also to reduce the presence of non-native woodland tree species such as Sycamores and Horse Chestnut. Felling created opportunities for ground flora to develop and also ultimately giving the woodland a more complex structure. 1500 young trees of local provenance were planted, particularly Black poplar one of Britain’s rarer trees.https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/black-poplar/

These young trees also helped create more diversity and structure to further enhance the woodland. Glades were created and bat boxes put up to further encourage and support woodland specialist species.

The aquatic element focused on the creation of a fish pass or channel which would by pass the obstacle of the weir. The weir is located on the section of river that runs adjacent to the reserve. The new channel or fish pass would allow fish and other aquatic species to safely navigate upstream to perform vital breeding and feeding behaviours.

The 110m long channel followed the path of the original drainage ditch, water was diverted in by the construction of a small concrete side-weir on the right hand bank of the river. Initially the existing channel was excavated removing the built up silt. After this gravels could be added, these were held in place by retained lengths of the felled timber from the woodland improvements.  Along the channel bed pools and riffles were created, these areas of shallow water would provide breeding and resting places for fish.

Wire gabions filled with larger stones were installed at the start and finish of the channel to provide suitable erosion control. Larger rocks were strategically placed at the weir end of the channel to create a faster flow to attract fish species in and upstream.

Impacts of the project:

The fish pass quickly naturalised and added a much appreciated extra element of interest and intrigue to the site. Particularly the sound of babbling water created a relaxing and usual sound (especially for East Anglia!) that hadn’t been there before. This movement and sound in turn attracted Grey Wagtails to nest,many fish species and consequently King Fishers and even Otters to hunt and forage.

The woodland improvements have particular impacted the bat populations which are thriving.

Common and Soprano Pipistrelle bats have roosts in the wood. Noctules can be detected hunting high over the tree canopy and Daubenton’s very visible gliding low over the river in the summer evenings.

The woodland is also supporting rare fungi and highly specific invertebrate species which specialise in the ephemeral conditions created by the watery seeps that are numerous around the woodland.