Recent fishway monitoring across the 2015/16 wet season has revealed some interesting results with a high abundance and diversity of juvenile fish species recorded successfully ascending the regions fishways (Figure 1). Fishway trap monitoring was undertaken on Lagoons and Fursden creeks within the Pioneer River Catchment (Mackay) and on Boundary and Tedlands creeks in the Rocky Dam Creek Catchment (Koumala).

Fishway assessment revealed large numbers of fish, with up to 5764 fish successfully ascending the Lagoons Creek full width rock ramp and culvert baffle fishway (Table 1) in just under one day (21.45 hours) and 3863 fish ascending the Boundary Creek partial width concrete cone fishway (Figure 3) in just over one day (28.5 hours (Table 2)). Tedlands Creek partial width rock ramp fishway (Figure 5) in Koumala recorded 2454 in 24 hours (Table 4) and Fursden Creek full width rock ramp fishway (Figure 4) recorded 2407 fish in 26 hour period (Table 3).

Significantly, the large numbers of fish migrating through Lagoons Creek full width rock ramp (Figure 2) and culvert baffle fishway (5764 in 21.45 hrs) were higher than fish numbers recorded migrating through vertical slot fishways on Australia’s two largest rivers, the Murray River (maximum 4415 fish per day) in Victoria (Stuart et al. 2008a) and Fitzroy River (maximum 3317 fish per day) in Queensland (Stuart et al. 2007). These recent fishway sampling results highlight the importance of facilitating fish passage in small ordered waterways for maintaining fish populations in the Mackay/Whitsunday region.

Based on the ‘river continuum concept’ whereby large ordered rivers such as the Murray and Fitzroy rivers contain a greater amount of energy sources and habitats types than low ordered short coastal streams like Lagoons Creek (Strahler stream order 1), and therefore should contain a higher diversity and biomass of fish species. You would therefore expect there to be a higher number of fish migrating through these larger river systems compared to small ordered streams (1-3). However, these latest fishway monitoring results suggest this may not always be the case.

These results raise several questions:

1. Why do these fishways on small ordered waterways pass comparable, and in the case of Lagoons Creek, greater numbers of fish than fishways on the two largest river systems in Australia?
2. Are fish, particularly small bodied and juvenile fish species purposely selecting small ordered waterways to undertake upstream migrations – as these waterways potentially offer refuge habitats with less apex aquatic predators than larger rivers, and therefore offer fish a greater chance of evading predators and reaching sexual maturity?
3. Or do smooth- sided vertical slot fishways (≥97 mm head difference between cells) provide adverse swimming conditions for some small bodied and juvenile fish species?

Recently constructed fishways in the Mackay Whitsunday region were designed with deep pools and small drops between ridges (57 mm for the smooth sided concrete cone fishway, and 80-90 mm for the rough finish rock ramp fishways) to reduce turbulence and provide conditions suitable for juvenile and small bodied fish species, such as empire gudgeon. In Queensland, juvenile empire gudgeon undertake a mass migration from estuarine environments to upstream freshwater wetland habitats during the summer wet season (Dec-April), and were recorded successfully ascending all four fishways. These fish can be very small (12 mm), and possess weak swimming abilities, so smooth sided fishways with large drops between pools (i.e. vertical slot fishways constructed in QLD pre 2010) may create adverse conditions for this species to successfully migrate through.

Other interesting fishway monitoring results included the capture of juvenile barramundi, as small as 43 mm (average 57 mm), migrating through the Boundary Creek concrete cone fishway. These are some of the smallest barramundi ever recorded successfully migrating through fishways in Australia. The smallest was a 38 mm barramundi successfully ascending a partial width rock ramp fishway on Alligator Creek, a short coastal 5^th ordered Strahler stream 20 km’s south of Townsville (Moore & Marsden 2013).

The small size of juvenile barramundi migrating through the Boundary Creek fishway (in just 3.5 days of sampling) when compared to the Fitzroy River Barrage vertical slot fishway is significant. Stuart and Mallen-Cooper (1999) monitored the vertical slot fishway on the Fitzroy River (38 paired samples (24 hr) – top and bottom) across 16 months and only recorded barramundi >200 mm successfully ascending to the top of the fishway. The average size of barramundi recorded migrating through the Boundary Creek concrete cone fishway was 57 mm (n=19). The Boundary Creek fishway (Figure 1) comprises a head difference of 53 mm between cells and is located on a Strahler stream order (SSO) 3, while the Fitzroy River comprises 97 mm head difference between cells and is situated on a SSO 9.

This again raises further important questions:

1. Are small juvenile barramundi (< 200 mm) purposely targeting small ordered streams to migrate upstream into wetland habitats i.e. Boundary Creek (SSO 3) and not the Fitzroy River main channel (SSO 9)?
2. Or, do vertical slot fishways with a ≥97 mm head difference between cells produce characteristics that prevent small juvenile barramundi (< 200 mm) from successfully ascending to the top of the fishway?
3. Or is it the attracting flows and/or the fishway entrance design that prevents small juvenile barramundi (< 200 mm) from locating fishways in large rivers?

Table 1. Lagoons Creek fishway monitoring results

Table 2. Boundary Creek concrete cone fishway monitoring results

Table 3. Fursden Creek fishway monitoring results

Table 4.Tedlands Creek fishway monitoring results.

References

Stuart IG, Baumgartner LJ and Zampatti BP (2008a) Lock gates improve passage of small-bodied and crustaceans in a low gradient vertical-slot fishway. Fisheries Management and Ecology 15, 241-248.

Stuart IG, Zampatti BP and Baumgartner LJ (2008b) Can a low gradient vertical-slot fishway provide passage for lowland river fish community? Marine and Freshwater Research 59, 332-346.

Stuart IG and Mallen-Cooper M (1999) An assessment of the effectiveness of a vertical-slot fishway for non-salmonoid fish at a tidal barrier on a large tropical/sub-tropical river. Regulated Rivers: Research and Management 15, 575-590.

Moore M and Marsden T (2013) Alligator Creek fishway and fish community sampling report.
Fisheries, QLD, Mackay