Community Research and Development Information Service - CORDIS


SILVER EEL Report Summary

Project ID: Q5RS-2000-31141
Funded under: FP5-LIFE QUALITY
Country: Netherlands

Assessment of turbine passage & mortality of silver eel

In the current project, silver eel passage and turbine-related injuries at Linne hydropower station has been estimated in two different ways: The first method is the conventional method by netting eels directly at the outlet of turbine 4 of Linne hydropower station. The second method is a novel telemetry method based on the transponder technique (Nedap Trail System (Registered). The results of the telemetry method provide valuable information on the cumulative damage due to passage of two hydropower stations at Linne and Alphen. The results are summarised in another result section of this document.

In the turbine netting experiments, a total 1196 eel were captured during 17 samplings, most of the silver eel occurred in the length class of 60 – 69 cm. The number of yellow eel passing the turbines is very low, counting 16 individuals (1.34 % of total catch). The increase of the number of silver eels passing the turbine starts late September and correspond to an increase of the river discharge. However, not each increase of river discharge implicated a migration event. The migratory activity of eel, as shown by checking the nocturnal partitioning of turbine passage, started between 19:00 and 20:00, just after the darkness fell and less than 50% of the migrating silver eels passed the turbines before midnight. After midnight the number of eel per sub-sample decreased again. These results fully correspond to the observations made by the telemetry experiment. It is expected that during the night of October 26 – 27, when breakage of the net occurred due to an excess of turbine flow, the amount of eel through Linne hydropower station has been the largest, considering both the detection rate of transpondered eels and the result of the Migromat (Registered).

The total of injured eels (non-lethal + lethal) is 34.0 % of the total of eel that passed the turbine. The total of lethal injuries amounts 24% of the total of eel that passed the turbine, however, this is likely to be an overestimation as part of the injured eels that have been defined as lethally injured still were alive and might survive the injury. The non-lethally injured eels correspond to 10% of the total of eel that passed the turbine. These specimens are likely to be able to, although with an unknown delay, continue their migration. The mortality is clearly related to turbine flow and the mortality rates found at 30 and 50 m3xs-1 correspond to the results of earlier investigations at Linne hydropower station. A clear relation was also found between the mortality and the length of the eel at 30 m3xs-1: larger eel showing higher mortality than smaller eel. At turbine flows of 50 and 100 m3xs-1 only a small length-effect was found. Overall, highest mortality rates are found for the 70 – 79 cm length class.


Bruijs MAARTEN, (Specialist)
Tel.: +31-26-3563573
Fax: +31-26-4454659
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