Rivers & Streams
Case study: Understanding eel ecology of a whole Norfolk River catchment
The Sustainable Eel Group put in a bid to the European Maritime and Fisheries Fund (EMFF) to undertake a comprehensive study of European Eel within the River Glaven catchment. ECON's role within this project has been to carry out electrofishing surveys, analysis and reporting, coordinating with colleagues at University College London and the Zoological Society of London, who are carrying out fyke-net surveys and tagging eels respectively.
The aims of the project are to provide an understanding of eel distribution, movements and habitat use in the Glaven catchment, to inform conservation and management measures, and to provide an assessment of methods used for monitoring eels in this context.
The fieldwork entailed catchment wide eel surveys using fyke netting, electrofishing and PASE (Point Abundance Sampling by Electrofishing). The latter technique involves fishing a specific location (or point) without moving the anode. At least 5 electrofishing and fyke surveys were constant between years, and 10 of the fyke net sites were sampled by electrofishing each year in order to compare methods.
Tracking was used to understand eel movements, and eel habitat use was investigated by using macro and micro habitat scale descriptors.
The results showed that eels were generally present in low numbers at most sites. Bayfield and Thornage appears to provide some of the best habitat. Examination of length frequency showed that a range of lengths were caught, with most small fish from Natural Surroundings, and larger fish from a variety of locations.
Analysis of habitat variables showed some possibility of habitat selection. Eels were found to avoid gravel, and select roots. There was also a weak link with silts.
It is anticipated that further work and analysis to be conducted in 2018/19 will result in a greater understanding of eels ability of pass engineered river infrastructure during migration, to quantify the intrinsic value of floodplain wetland, lakes and ponds, to provide a rigorous scientific basis for selection of conservation measures, and to produce a methodological toolkit for monitoring eels.