The construction of large infrastructure in tropical river systems that alters habitat from lotic to lentic can significantly impact local fish communities, however, the details of this alteration remains poorly understood. As part of the Rookwood Weir Project, which included the construction of a 20 m high weir on the Fitzroy River in Central Queensland, we conducted comprehensive studies to establish a baseline of fish communities both upstream and downstream of the project site prior to construction. This baseline sampling, carried out at 22 sites, employed electrofishing techniques to assess fish communities before and after the wet season, reflecting periods of high and low fish community populations.
To date, pre-construction sampling has recorded 10,316 individual fish from 35 species. Diadromous species dominated downstream of the Fitzroy Barrage at the tidal interface, with a diverse array of lotic species occurring upstream, particularly in the footprint of the future weir. Endemic species such as Leathery grunter and Southern saratoga were relatively common, while introduced species, particularly Tilapia, were also prevalent, especially in existing weir pool habitats.
This baseline data is crucial for ongoing future assessments, aiming to demonstrate the impacts of habitat changes within the weir pool on fish communities, as well as potential changes in pest fish species. The current findings indicate that the Fitzroy River sustains a diverse and generally healthy fish community, which ongoing environmental flows and rehabilitation programs aim to preserve.