Fresh water systems
Monitoring and surveys

Elver Finder (ELFI)

ELFI has been developed by Waardenburg Ecology from the need to nvestigate the migration of the glass eel in a standardised, reliable and continuous manner. Therefore, we developed the glass eel detector (or ELFI), which we have used in a wide variety of locations and in both fresh and salt waters, and at weirs and fish passages, in large and small waters.

Glass eels are young eels that migrate from the sea up the rivers and mature in fresh water systems. Due to barriers such as weirs and dams, few glass eels ultimately reach their maturing areas. The eel now has the status of 'critically endangered' on the international IUCN Red List.

Migration research

ELFI is a collaborative product of Waardenburg Ecology and Visserij Service Nederland. ELFI is used for monitoring eels migrating upstream, in the life-stages from glass eel to yellow eel. ELFI is often combined with VIE tagging (Visible Implant Elastomer), a method of colour-coding animals. These two techniques answer questions such as:
  • Where, when and how many glass eels migrate?
  • How long do glass eels spend trying to pass a certain barrier?
  • How quickly, and in what quantities do glass eels use a fish passage?
  • What are the migration routes of glass eel?

For whom?

We conduct research with ELFI for governments, water authorities, interest groups (NGOs) and various research institutes.
Check out the ELFI website here