Rocky Dam Catchment Fishway Monitoring 2020

In February 2020, Catchment Solutions conducted fishway monitoring at a cone-ramp fishway which provides fish passage between upper-tidal estuarine habitats and a significant wetlands complex, at Koumala in the Rocky Dam catchment south of Mackay. The wetlands are surrounded by an extensive earthen bund wall, which features two fishways allowing fish to enter the wetlands. Importantly, the extensive wetlands provide an abundance of food and refuge habitat for fish and bird species and also provide habitat for saltwater crocodiles.

Figure 1. Image of the large wetlands which provide an abundance of habitat and refuge for native fish communities.
The cone-ramp fishway was constructed at the site in November 2015, along with a formal causeway and spillway allowing water to exit the wetlands during wet-season flows. Fish utilise the fishway through firstly being instinctively attracted to the freshwater flowing out of the wetlands. They then enter the fishway and use their burst speed to ascend through the ridges of the fishway, whilst also being able to rest in the large pools between the ridges as they make their way upstream. In central Queensland, it is generally the juvenile young-of-year recruits which migrate from upper estuarine habitats into freshwater wetlands, meaning that providing sufficient resting areas and suitable conditions throughout the fishway is critical to ensure small fish are able to ascend.

Figure 2. Left; cone-ramp fishway following dry-season construction in late 2015 and right; during fishway monitoring, with the fish trap visible at the top of the fishway.
The monitoring was strategically timed to coincide with wet-season flows during the warmer months, in the anticipation that these conditions would result in a high number of juvenile fish migrating up the fishway to enter the wetlands. Overall, an average of 1410 fish/day were captured migrating up the fishway, which was made up of ten species. This includes an average of 86 barramundi captured per day, which is among the highest numbers of barramundi ever recorded migrating up a fishway per day. Perhaps more importantly, the size range of these barramundi ranged from as small as 25mm through to 108mm, showing these fish are likely only weeks old, and utilising the fishway for life-cycle dependent migrations into the wetlands to utilise the abundance of food and refuge to grow rapidly. The results obtained show the value of providing aquatic connectivity at sites such as this, between fresh and saltwater habitats. This is not only of critical importance for general fish community health, but also for ensuring sustainable populations of species of socioeconomic value to commercial and recreational fisheries.

Figure 3. Top; image of a typical trap haul during the monitoring showing barramundi amongst other species, bottom left; typical size range of young-of-year barramundi recorded ascending the fishway and bottom right; the smallest individual barramundi recorded at only 25mm.