ASEA Ecology Mitigation and Flood Defence Project

Eel migration is going swimmingly in local water outfalls thanks to steps taken by the Avonmouth Severnside Enterprise Area (ASEA) Ecology Mitigation and Flood Defence Project team to support them.

Over the past few months, the team has been busy upgrading eel spring retarders at tidal gates at outfalls across the 17km project, including Cake Pill, Chestle Pill and New Pill tidal outfalls in South Gloucestershire. The retarders are a spring or tension device used to hold the tidal gate open and slow the closure of the gate on the incoming tide. This means that eels can pass through more easily over a longer period.

European eels once thrived in the UK, but the population has dropped dramatically since the 1980s, declining by 95 per cent. The species is now classified as critically endangered. One of the reasons for this is that eels’ migratory pathways are frequently blocked. Removing barriers and installing eel spring retarders and eel passes in places where migration has been disrupted helps to conserve this species. It is a legal requirement to maintain eel passes to a functional standard under the Eel Regulations 2009.

Tidal gates are an example of structures that prevent eels from moving into a watercourse. Eel spring retarders solve this problem by holding tidal gates open for longer at the point at which the water level on either side is equalised. Eels can then migrate upstream where the gate would otherwise be closed. Spring retarders are easy to install, require minimal maintenance, and are a low cost, flexible way to improve eel and fish passages at tidal gates.

The refurbished spring retarders are the latest in the project’s work to conserve endangered species. This spring, the project team released water voles onto a new home at one of the project’s new wetlands at Hallen Marsh near Bristol. Water voles are also amongst the most endangered species in the UK. The wetland, at Hallen, is part of over 80 hectares of new wetland habitats created by the project.