October 2020 - November 2022 Southern Water

FiveRivers was commissioned by Southern Water, as part of their Asset Management Plan (AMP) 7 Water Industry National Environment Programme (WINEP) investigation, to conduct a five-year trap and transport project targeting invasive non-native species (INNS).

The primary aim of the project was to mitigate fish escape from a reservoir by removing from the waterbody as many of the target INNS as practicable given various constraints. As part of a multi-year project that started in 2020, removal works are carried out over a two-week period each year, and are still ongoing. Two methods were utilised within the reservoir to target invasive fish species of interest; rod and line angling and fyke netting. Any American signal crayfish caught in fyke nets were removed from the waterbody.

Any target fish including European eel caught during the project were translocated from the reservoir to an agreed control point further downstream on the river, as stipulated by the Environment Agency under the European Eel Regulations 2009. The work is a requirement to improve the WFD status of the waterbody, which is a designated Site of Special Scientific Interest (SSSI) and Local Nature Reserve (LNR).

Project requirements

The problem

Each year, FiveRivers undertook two consecutive weeks of boat fieldwork, to remove as many of the non-native invasive fish species as possible within the time frame.

Fyke netting and rod and line angling are the two primary methods of fish removal given the size and nature of the waterbody. Data recorded on numbers of fish caught, length and weight, as well as scale samples were taken to enable ageing of fish caught. Through this, we were able to provide the client an idea as to the different age classes present, and how fast they are growing, and their ability to reproduce in situ.

We ensured strict bio security procedures due to presence of various non-native invasive species known to be prolific on site, and to prevent any further spread.

Our approach

The solution

Our initial approach in 2020 was to carry out two weeks’ worth of fyke netting back to back, however in 2021, there was a methods appraisal and a scope change to allow one weeks’ rod and line angling as a proposed alternative method, as a trial to compare it’s efficacy to that of fyke netting. Rod and line proved to be very effective, and as such we continued to conduct one week rod and line angling and one week of fyke netting to target all the different age classes present.

As always, our approach is to work safely, and as efficiently as possible to achieve the best possible outcome in terms of client deliverables and satisfaction, as well as the best possible outcome for the environment.

Non-native invasive fish species captured were humanely euthanised using anesthetic licensed under Schedule 1 of the Animals (scientific procedure) Act 1986 and disposed of responsibly using registered waste carriers.

Project outcomes

The results

This project was delivered successfully, removing a total of 253 of the target non-native invasive fish species, equalling approx. 62KG, a further 214 Non-target native fish were captured, recorded and released back in to the reservoir.

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Tom Grayling

Director of Monitoring & Natural Capital

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