Assessing the requirement for fishways on Gingin Brook
The fish fauna upstream and downstream of four barriers (dams) on Gingin Brook were sampled during November 2003 in order to determine whether such barriers pose a significant obstruction to fish migration. A total of 773 fish from eight species were captured during the sampling period. Six of these species are endemic to the freshwaters of south-west of Western Australia including (in order of abundance): western pygmy perch, nightfish, western minnow, freshwater cobbler and mud minnow. Two further species are essentially estuarine and are also restricted to this region: Swan River goby and big headed goby. The feral mosquitofish, a native to eastern and south-eastern United States, was also relatively common throughout Gingin Brook. There were greater abundances and mean densities of all native fish species at sites immediately downstream of the major obstructions on Gingin Brook than upstream, with the exception of the big headed goby, which had similar densities. Overall, there were significant differences between the density of fish (all species combined) below the barriers than above (P = 0.001).
Between sites upstream and downstream of obstructions, there were significantly more western pygmy perch (P ≤ 0.05) and nightfish (P ≤ 0.1) below structures with the mean density of these two species at sites immediately downstream of obstructions being 0.46 (±0.13) and 0.33/m2 (±0.14), respectively, compared with densities of 0.08 (±0.05) and 0.05/m2 (±0.05), respectively, immediately upstream of the obstructions. There was also a considerably greater mean density of western minnows below the obstructions compared with above, however, due to a high variation in number, this was not found to be significant.
It appeared that the major obstruction to fish movement on Gingin Brook, as reflected by the greatest difference in abundances in most native fishes downstream and upstream of the obstruction, was the town weir. The western pygmy perch, western minnow, nightfish and Swan River goby were all recorded in far greater density downstream of the weir when compared with upstream. The gauging station at Mortimer Rd and the weir at Cheriton Estate also pose significant barriers to fish migrations.
It is therefore recommended that initial consideration be given to the most costeffective design for the greatest impediment on Gingin Brook, the town weir, and its effectiveness assessed by an ongoing monitoring program similar to that which has occurred on the recent fishway projects (see Morgan and Beatty, 2004 a, b, c). Once the effectiveness of this initial fishway has been assessed and confirmed, it is recommended that consideration then be given to fishway constructions on the Mortimer Rd gauging station and the Cheriton Estate weir.
|Murdoch Affiliation:||Centre for Fish and Fisheries Research|
|Series Name:||Murdoch University Report to the Gingin Land Conversation District Committee|
|Publisher:||Murdoch University. Centre for Fish & Fisheries Research|
|Copyright:||2004 Murdoch University. Centre for Fish & Fisheries Research|
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