Prior to installation of a fishway at a road crossing in 2001, a remnant population of endangered Macquarie perch (Macquaria australasica) was confined to a 6-km section of the Cotter River, Australian Capital Territory. The purpose of the fishway was to provide passage past a barrier and to increase the extent of spawning grounds for M. australasica to an additional 22 km of river. The aim of the current study was to quantify the extent of nursery grounds of M. australasica in the Cotter River catchment by developing and applying a rapid, non-destructive technique for surveying juvenile M. australasica. From October to January in 2006–07 and 2007–08, pools were surveyed by snorkelling in the lower Cotter River to detect juvenile and larval M. australasica. The 9-km study reach consisted of the four pools immediately upstream of Cotter Reservoir, seven pools further upstream but still downstream of the rockramp fishway and 14 pools upstream of the fishway. In 2006–07, juvenile M. australasica were detected at 22 of 25 pools, including 13 of 14 pools upstream of the fishway. In spring/summer 2007–08, low visibility conditions frequently occurred throughout the river preventing survey on several occasions. However, recruitment of M. australasica was again detected upstream of the fishway. The increased extent of the nursery grounds of this M. australasica population has proven to be timely as an enlargement of the Cotter Reservoir, due for completion in 2012, will inundate more than 90% of prefishway nursery grounds in the Cotter River. Our study has demonstrated the benefit of installing a fishway in expanding the nursery grounds and the number of recruits of a remnant population of the endangered M. australasica. We also demonstrate the benefits of employing a visual survey technique to quantify the extent of the riverine nursery grounds of a fish population.
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Vol. 60 • No. 2