Native fish can’t jump

Apr 26, 2016 |

Reef Catchments and local landholders are working to improve the health of the O’Connell River through removing barriers and improving in-stream habitat.

To many, paradise is living and fishing in and around the Mackay Whitsunday region with many visitors coming to the region each year for the opportunity to catch a Barra or Jungle Perch. The region is blessed with many beautiful streams and river to explore with the potential to catch a fish in the process. However, over a century of development has impacted on the ability of diadromous fish species migrating up through the river systems.

Diadromous fish move between the fresh and saltwater environments for some aspect of their lifecycle. The movement of Diadromous fish along our waterways is considered crucial to their life cycle and breeding patterns. In Mackay-Whitsunday there are 48 freshwater fish species and half of those are ‘diadromous’, Queensland’s two most important and iconic in-shore commercial net species, barramundi and sea mullet (Williams, 2002) require unimpeded access between freshwater and estuarine habitats to maintain sustainable populations (Mallen-Cooper, 2000)

Native fish species also require the right in-stream conditions to maintain populations including habitat complexity and deep pools for sustaining populations during the dry season.

With funding through the Australian Governments Reef Programme Reef Catchments has been working with Landholders to improve aquatic health and connectivity to implement activities along the regions rivers and waterways. Works being undertaken include revegetation along riparian zones, which will provide shade to cool the river, bank stabilisation and the removal of fish barriers and construction of fish ladders. Undertaking these activates is essential to sustain fish populations and ensure that fish are able to deal with any future pressures.

Fish movements within the river system

Native fish, such as Barramundi, swim up the creeks as small juveniles and then use that safe habitat to find plentiful food away from predators. They may stay there more than a year before they grow big enough to swim back downstream and, as bigger fish, prosper in the major estuaries opening into the sea and spawn. If those juveniles are blocked from migrating upstream, they must instead take their chances among the bigger predators downstream and are much less likely to grow to adulthood.

Taking this into consideration Reef Catchments has been constructing fish ladders on some of the rivers barriers to allow greater migration up and down stream. One fish ladder constructed was at Forbes Rd crossing.

Forbes Road Concrete Causeway Fish Barrier

A concrete causeway on Forbes Rd 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 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.

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

Aquatic habitat improvement on the O’Connell River

Reef Catchments has been working with local landholders to implement a range of activities along the O’Connell River to improve aquatic health and reduce the loss of productive agricultural land. Works being undertaken include revegetation, reprofiling and rock toe reventment to reduce eroding banks and imbedding large woody debris within stream to increase habitat complexity.

The activities being undertaken along the O’Connell River will provide significant benefit to native fish species opening up the rivers and providing habitat and good water quality to ensure healthy and sustainable populations for the years ahead.