Downstream Passage Performance of European Silver Eels ( Anguilla anguilla ): The Importance of Phenotypic Variation and Rack Design

This is the authors' abstract. We don't add key points for this paper.

Anthropogenic structures such as dams, weirs, and hydropower plants constitute adverse obstacles to diadromous fish migrating between their rearing and spawning grounds. During their downstream spawning migration, catadromous European eel ( Anguilla anguilla ) frequently encounter hydropower plants, often resulting in severe injury or mortality. Accordingly, promoting successful passage is necessary to improve migratory conditions for this critically endangered species. In large‐scale flume trials, we used time‐to‐event analysis to compare the passage rate of eels encountering three types of angled racks with 30 mm bar spacing and bars oriented (i) horizontal and streamwise, (ii) vertical and streamwise, and (iii) vertical and angled. In addition, we investigated the effects of eel individual behavioral type, as measured by distance travelled in an open field test, on passage rate. We found that passage rate was positively affected by individual activity in the open field test, whereas rack type played a less important role. However, the vertical and streamwise rack allowed more eels to pass through the racks (30%), instead of being guided into a bypass, compared to the horizontal and streamwise and vertical and angled racks (9% and 4%, respectively). The results imply that fish passage solutions should be designed to guide as many individuals of different phenotypes as possible to the bypass, but that currently used downstream solutions for silver eel may instead favor more active individuals.