Forbes Road Rock-ramp Fishway

Case study

The Mackay Whitsundays region is blessed with a diverse array of freshwater fish species, many of which undertake migrations during their life history.

reef-catchments-forbes-road-oconnell-river-rock-ramp-fishway

Fish Barriers & Mackay Whitsunday Fish Species

The Mackay Whitsundays region is blessed with a diverse array of freshwater fish species, many of which undertake migrations during their life history. Some of these migrations are short and confined wholly to freshwater habitats, while some migrations occur across vast distances and between varying habitats, including between freshwater and near-shore marine environments. Of the 48 freshwater fish species found to occur in the MW region (Moore and Marsden, 2007), almost half (48%) require unimpeded access between freshwater and estuarine habitats to complete their life cycle or maintain sustainable populations.
Migration strategies between key habitats have evolved for a variety of reasons, including;

  • Feeding and reproduction purposes,
  • Avoidance of predators,
  • The utilisation of nursery areas (juvenile fish),
  • Dispersal – to avoid being trapped in drying waterholes
  • Maintain genetic diversity

However, barriers such as culverts, pipes, road crossings, weirs, dams, flow gauging structures, bunds (or ponded pastures) and sand dams prevent connectivity, impact fisheries’ productivity and create environmental conditions favourable for invasive fish species. Barriers to fish migration have the greatest impact on diadromous fish species – those that migrate between the sea and freshwater habitats to breed and/or sustain fish populations. These include important commercial, recreational and indigenous fishery species such as barramundi (figure 1), mangrove jack, sea mullet and jungle perch.

Man holding huge barramundi.

One metre long barramundi sampled (electro-fishing) while undertaking fish community monitoring in the lower freshwater reaches of the O’Connell River.

Forbes Road Concrete Causeway Fish Barrier

A concrete causeway on Forbes across the O’Connell River in Bloomsbury was preventing the migration of fish species and impacting local fish populations. The causeway barrier consisted of a series of pipe culverts which ‘dropped’ into the river below. The velocity of water flowing through these culverts was too fast for fish to swim through and the drop on the downstream side of the pipes into the river was too high – as native fish, unlike their northern hemisphere cousins; Atlantic salmon, can’t jump.

So in November 2013, Reef Catchments funded Catchment Solutions to construct a partial width rock ramp fishway (Figure 1) so that the fish can ascend through the fishway, negotiating the causeway barrier into important upstream habitats. Fish are then attracted to the fishway as flows pass through it. The fishway consists of a series of pools interspersed by rock ridges. The rock ridges consist of large 1.5 m boulders, with small gaps in-between. The drops between the pools are 75 mm. Fish use their ‘burst speed’ to negotiate each rock ridge in the fishway, before resting in the pool.

O'Connell rock-ramp fishway.

Nature-like rock ramp fishway, Forbes Road, O’Connell River.