Monitoring changes in the Crawford River fish community following replacement of an effective fishway with a vertical-slot fishway design: Results of an eight year monitoring program
Non Technical Summary
Many fish that live in coastal streams and rivers need to migrate at some stage in their life cycle. In streams with barriers such as weirs, this migration can be inhibited or prevented, and fish species can become locally extinct. Providing passage for migrating fish is therefore a fundamental tool in rehabilitating degraded fish habitat in coastal waterways.
The Buladelah weir had an ineffective submerged orifice pool and weir fishway for nearly 30 years. Sampling in 1992 found only 9 fish species in the Crawford River upstream of the weir compared to 15 in the adjacent Myall River which had no weir. The fishway on Buladelah Weir was upgraded to a vertical-slot design in February 1993 and the response of the Crawford River fish community was monitored over the next 7 years. This is one of the longest evaluation periods for a fish rehabilitation project in NSW.
Seven years after construction of the vertical-slot fishway, the fish community of the Crawford River is still significantly different to that of the Myall River. However, a trend of significant improvement was documented, with 16 fish species recorded in the Crawford River. Further, significant improvements have been demonstrated for three species, with populations of migratory empire gudgeons and striped gudgeons having greatly increased in the Crawford River and juvenile striped mullet (which were previously inhibited by the original fishway) are now present in the Crawford River.
Fishway trapping in October 1999 demonstrated that all species and size classes of fish were capable of moving up and through the new fishway. Therefore, the lack of a rapid recovery of the Crawford River fish community is not due to an ineffectiveness of the fishway itself. Rather, natural water quality differences between the Crawford and Myall Rivers may be responsible for the different fish communities.