Fish prefers less wind in the willows
From the August 2006 edition of Agriculture Today.
More than 2100 exotic tree species, such as willow, tree of heaven, honey locust and privet, have been poisoned along the banks of the Upper Castlereagh River, in a bid to improve the health of the waterway, home of the increasingly rare river blackfish (Gadopsis marmoratus).
This work is part of a two year project funded through the Central West Catchment Management Authority to establish demonstration reaches in the river.
“River blackfish are secretive bottom dwellers and can grow to around 30 centimetres,” Shaun Morris, NSW Department of Primary Industries conservation management officer at Dubbo, said.
“They feed mainly on aquatic insects such as caddis fly larvae and beetles but are also known to consume small crustaceans, molluscs and fish.
“River blackfish deposit their eggs in hollow logs and rock crevices and are highly susceptible to sediment accumulations resulting from the spread of exotic tree species such as willows,” Mr Morris said.
As willows establish themselves along a river bank they also spread into the channel habitat, retarding stream flow and increasing the amount of sediment laid down during flooding.
This shallows out deep pools, filling in rock crevices, hollow logs and other structures.
Exotic tree species are also known to inhibit the establishment and growth of the preferred native riparian vegetation that helps to mitigate sediment runoff from adjacent agricultural activities.
These works are the start of a range of actions to improve the health and biodiversity of the Upper Castlereagh River.
“Future activities will include fencing off riparian zones and establishing off stream water points with tanks and troughs, to preserve bank stability and improve water quality,” Mr Morris said.
In addition, sediment slugs and willows that have established within the stream will be removed at specific sites.
There will be improvements to local road crossings as well as the creation of a log deflector jam (purpose built snag complexes) to protect eroded banks, maintain deep pools and provide habitat for fish and other aquatic organisms.
As part of these activities local landholders have provided in-kind contributions by poisoning exotic tree and shrub species, fencing off riparian zones and putting time and physical effort into improving the scope of works associated with the project.
The local community can learn about the results of the project through open field days planned for later this year.
Contact Shaun Morris, NSW DPI Aquatic Habitat Rehabilitation, Dubbo, (02) 6881 1270.
