Abstract:
Fish passes, traditionally designed to facilitate upstream migration,
are now increasingly recognized for their potential to support
bidirectional fish movement and to improve habitat availability for
potamodromous fish. This four-year study at the Ottensheim-Wilhering
Hydro Power Plant on the Austrian Danube tracked the migration patterns
of the common nase (Chondrostoma nasus ) using five PIT tag
antenna arrays installed in a 14 km long, near-natural bypass system,
which integrates two natural tributaries.
A total of 190 nase were tagged and released in the Danube upstream the
hydro power plant, and fish movement data were collected from November
2020 to June 2024. A large percentage of the tagged individuals entered
the fish pass from upstream. Over the years, many individuals utilized
the bypass system for extended periods and were observed repeatedly
visiting the fish pass, highlighting its role not just as a migration
corridor but also as a spawning and feeding habitat.
These findings underscore the multifunctionality of near-natural fish
passes, which not only restore longitudinal connectivity but also
provide critical habitats for various life stages of rheophilic fish.
The study challenges the assumption that fish passes are ineffective for
downstream migration and suggests that such systems can play a
significant role in supporting potamodromous fish populations in highly
regulated rivers like the Austrian Danube.