The population of the European eel (Anguilla anguilla) is at a dramatically low level. One significant risk for the descending parental fish on their way from the fresh water habitats to the spawning area in the ocean is to pass hydroelectric power plants with turbines. The fact that the migration of eels is a mass event that appears over a few days/night per year, providing an opportunity for an early waning based “eel protecting operation” (EPO) at hydropower plants, without the necessities for time and cost intensive structural changes. An EPO may consist of a limited reduction of the flow velocity in front of a trash rack, an episodic opening of weir fields and/or a shutdown of the turbine.
The prerequisite for such measures, however, is the knowledge of when an eel migration will take place. The MIGROMAT®, invented and developed in 2000 by the Institut für angewandte Ökologie GmbH is the only early warning system for generating temporally precise and reliable predictions of downstream migration events.
For this purpose, the behavior of indicator eels is controlled continuously in order to detect significant indicators of a pre-migration restlessness, which affects the eels in the MIGROMAT® as well as wild conspecifics in the river. A MIGROMAT® consists of two tanks, each 4 m long, to keep 60 indicator eels for about 7 months. Each eel is individually marked with a 12x2 mm small RFID-transponder. The flow-through tanks are equipped with dividing panels with square openings surrounded by an RFID antenna to detect the movement patterns of the eels. If the PC detects characteristic changes in behavior and certain thresholds are exceeded, the early warning system alerts the power plant control center. This way, an EPO can be initiated before migrating river eels arrive at the hydropower plant. At the end of an operating season, the indicator eels are released.
Construction of the MIGROMAT®
MIGROMAT® at a hydropower site
Numerous and independent monitoring studies confirm that the MIGROMAT® protects between 75 - 95% of migrating descending eels. Actually, a total of 13 early warning systems are operating on the German rivers Regnitz, Main, Fulda, Werra and Weser, and at Maas and Lek in the Netherlands.
ADAM, B. & U. SCHWEVERS (2019): Effizienz des aalschützenden Betriebs der Kraftwerke Offenbach und Kesselstadt. - Wasserwirtschaft 109 (in Vorbereitung).
ADAM, B. (2018): Mit dem Frühwarnsystem MIGROMAT® abwandernde Aale schützen. - ZEK 6/2018, 68- 70.
THALMANN, M. (2014): Aalschonendes Betriebsmanagement. - Düsseldorf (Statkraft Markets GmbH), 33 S.