How the Proposed Traveston Dam on the Mary River will affect Endangered (EPBC Act )Aquatic Species
by Dale Watson, Mary River Catchment Co-ordinating Commitee (MRCCC)
The Mary River Catchment is home to several rare and threatened freshwater aquatic species. The recently proposed dam at Traveston on the main trunk of the Mary River will drastically affect four of these very important species, the Mary River Cod (Maccullochella peelii mariensis – Endangered under the EPBC Act 1999), the Mary River Turtle (Elusor macrurus - Endangered EPBC), the Queensland Lungfish (Neoceratodus forsteri – Vulnerable EPBC) and the Giant barred frog (Mixophyes iteratus – Endangered EPBC).
The Mary River Cod and the Mary River Turtle occur naturally in the wild nowhere else in the world. The Queensland Lungfish, now occurs naturally only in the Burnett and Mary river systems. This article will briefly look at the threats the proposed large dam at Traveston may have on these already threatened species that live along the Mary River and its tributaries.
Upstream Effects
Fish Passage: Although the knowledge and technology now exists to build suitable “fish transfer devices” (fish ladders and fish lifts), it is widely acknowledged that they are very difficult and expensive to construct for barriers with high dam walls (such as the proposed dam at Traveston). It is also recognised that, even with a fish transfer device, fish passage, genetic distribution and migration for spawning will never be returned to its natural state after the construction of a dam. This impediment could severely impact on the Mary River Cod and Queensland Lungfish (both of which are know to migrate over long distances, especially during spawning times). Recent electronic tracking studies have established that turtles do not enter fish transfer devices. This dam would also impede the flow of genetic material between upstream and downstream populations of the Giant barred frog as it will disappear from most of the impoundment perimeter
Flooding of Existing Habitat: The proposed dam site contains known habitat for the nationally endangered Mary River Cod, Queensland Lungfish and Mary River Turtle. Although these species can survive within impounded areas, they cannot breed in these impounded areas.
The Mary River Cod relies on deep, cool, shaded pools containing large woody debris (snags) for it to successfully breed. The Traveston dam will flood several of these known habitats on the Mary River and will not provide any similar habitat once completed.
Queensland Lungfish requires shallow flowing riffles and glides amongst dense beds of submerged aquatic plants to lay its eggs on. Again suitable lungfish spawning habitat will not exist within the new dam.
The Mary River Turtle utilises only sandy river banks to lay its eggs. The proposed dam will flood several known locations of this rare and critical nesting habitat. It is also believed that poor water quality due to a process known to occur in dams known as stratification (where deep, cooler waters, with little dissolved oxygen turn over when surface waters heat up) will also have dire effects on any Mary River Cod, Mary River Turtle or Queensland Lungfish that may survive within the dammed area.
The Giant barred frog is found in the tributaries of the Mary River where undercut banks, vegetation and deep pools are present. As the lower sections of many tributaries will be flooded riparian vegetation will be lost. Undercut banks are essential for egg deposition and these too will be lost. The frogs will disappear from the impounded areas.
Aquatic Weed and Algal Growth: The Traveston dam site will create a large expanse of relatively shallow still water, where the lack of flow, increased water temperature and stratification will create optimal growing conditions for aquatic weeds and algae. Excessive aquatic weed and algal growth create very unfavourable conditions for aquatic life (such as the Mary Cod, Lungfish and Mary River Turtle) in still water bodies by severely depleting the dissolved oxygen levels within the water. There are many sources of aquatic weeds already in the Mary Catchment (for example Cabomba, a weed of national significance, in nearby Lake McDonald) that will be very easily spread to the proposed dam. Once established in the dam these aquatic weeds and associated problems will be very easily transported downstream.
Exotic Fish Species: It is well documented that an impounded dam environment is far more suited to many exotic fish species, such as Carp and Talapia. The Mary River is one of the few remaining rivers in South East Queensland without an infestation of large exotic fish. If exotic fish species entered the proposed dam, they could be expected to proliferate in a short period of time and out compete any remaining native fish species (such as the Mary River Cod and Queensland Lungfish). Some exotic fish are known to predate on frog eggs and tadpoles and would add to the pressures on Giant barred frog populations living along tributaries of the Mary River. There would be a high risk of exotic fish species spreading both up and downstream of the proposed impounded area.
Downstream Effects:
Reduction in Flow: It is estimated that the mean annual flow of the Mary River will be reduced by up to 20 percent as a result of the proposed dam. There are studies that have directly linked the decline in the health and productivity of fish species to a reduction in flow volumes. Reduced flows would negatively effect populations of the Mary River Cod and Queensland Lungfish and other native aquatic species.
Loss of Riffles and Pools: The combined effect the proposed dam will have of reduced mean annual flow and the loss of channel forming high flows will dramatically change the shape of the Mary River downstream of the dam. The major impact expected from the change in flows will be the loss of the riffles (shallow water rapids) and pools along the Mary River. Riffles and pools are essential habitat for the Mary River Cod and Queensland Lungfish, with the Cod relying on deep shaded pools to breed and spawn in and the Lungfish needing riffles with aquatic plants to lay their eggs on. Riffles also provide the river with dissolved oxygen through aeration of the water. A loss of riffles will mean a reduction in the dissolved oxygen levels directly affecting the Mary River Cod, Queensland Lungfish and Mary River Turtle. Riffles are also very important breeding areas and habitat for many species of macroinvertebrates (waterbugs), which are a very important food source for the Mary River Cod, Queensland Lungfish and Mary River Turtle.
Channel Contraction: The lack of high flows that will result from the proposed dam, will also result in channel contraction and bed scouring downstream of the dam. As the channel contracts and the bed deepens, vegetation will likely begin to encroach further towards the river. The Mary River Turtle uses the sandy banks of the Mary River to lay its eggs and, as the vegetation encroaches into the contracting river channel, these important sandy banks will be lost to the Mary River turtle, making reproduction impossible.
Loss of Floodplain Connectivity: The decrease in high flows downstream of the proposed dam will mean less events where the floodwaters breach the high banks of the Mary River. The breaching of these high banks is very important to many aquatic species that rely on an interaction between the river waters and the water of off-stream wetlands.
Loss of Epiphytic Algae and Phytoplankton: The changes in flow caused by the proposed dam, especially release of water during normally low flow periods, will cause flushing of the natural epiphytic (attached) algae and phytoplankton that are an essential component of the food chain and important for juvenile Mary River Cod and Queensland Lungfish.
Sedimentation During Construction: The construction of the proposed dam will undoubtedly cause a large increase in sediment entering the Mary River. This will increase the river’s turbidity downstream of the proposed dam site, and directly affect the health of the Mary River Cod, Queensland Lungfish and Mary River Turtle, through decreased water quality, decreased native submerged aquatic plant growth and infilling of habitat pools.
Decrease in Large Woody Debris: The proposed dam will create a barrier to the transport of large woody debris downstream of the dam. Large woody debris is essential for the spawning and refuge of the Mary River Cod and habitat for the Queensland Lungfish and Mary River Turtle.
Release of Cold Water: If water releases from the proposed dam are not managed correctly and multi-levelled releases are not incorporated into dam operations there will be impacts on the Mary Cod, Queensland Lungfish and Mary River Turtle through thermal pollution. Water is often released from the bottom of a dam, where the water has a much lower temperature. Many studies have shown that cold water releases can be detrimental to many aquatic species spawning and life cycles (such as the Mary River Cod and Queensland Lungfish) and disrupt the availability of food throughout the food chain.
Decreased Riparian Seed Dispersal: The reduction in flows caused by the proposed dam may also decrease the natural ability of the Mary River to disperse very important creek-side (riparian) tree species (such as the Weeping Lilly Pilly). These tree species are essential in maintaining cool water temperatures and providing large woody debris essential habitat elements for the Mary River Cod.
Tributary Channel Incision: It is probable that the decreased flows caused by the proposed dam will cause channel incision (or stream bed erosion) as the normal flow of the tributaries enter the lower flows of the Mary River. Channel incision of the tributaries entering the Mary River will alter the habitats of the Mary River Cod, Mary River Turtle and Queensland Lungfish within these tributaries.
Increased Aquatic Weeds and Algal Growth: The stable base flows and reduced incidence of flood flow created by the proposed dams will create far more favourable conditions for aquatic weeds invasions and algal growth. As already mentioned, excessive aquatic weeds and algal growth create very unfavourable conditions for aquatic life (such as the Mary Cod, Lungfish and Mary River Turtle) in Stillwater bodies by severely depleting the dissolved oxygen levels within the water. With a very high likelihood that aquatic weeds and algal growth will become a problem in the impounded water above the dam wall, it is likely that the problems will be transferred downstream.
Mortality from Spillway: Sudden falls in water levels, caused by dam operation procedures, can cause fish stranding on and below spillways. There are also many reported cases of fish and turtles dying after being washed over dam spillways during high flows. The Mary River Cod, Queensland Lungfish and Mary River Turtle are very susceptible to this threat. | 
