Jason Higham provides us with an overview of work underway in the Coorong and Lower Lakes Ramsar Site that is trying to keep the Murray-Darling Basin’s only estuary connected to the river for some enigmatic fish species.
The Coorong, Lakes Alexandrina and Albert wetland (the site) is a ‘Wetland of International Importance’ under the Ramsar Convention. The site is well known for its importance nationally and internationally to waterbirds, but less for its highly diverse fish population, unique within the Murray-Darling Basin (MDB). Many of the endemic fish are species of national and state conservation significance, and are also important to the Traditional Owners of the site, the Ngarrindjeri.
The international importance of a Ramsar wetland for fish is determined by the diversity of fish species it supports (biodiversity) as well as the range of morphologies and reproductive styles (biodisparity).
In the case of the Coorong and Lakes, the site supports 43 fish species across a range of fresh water, estuarine, marine, and diadromous (fish that migrate between the sea and fresh water) species not found elsewhere in the MDB. Crucially, this represents more than 50 per cent of the fish species found within the Basin, highlighting the site’s importance nationally and internationally, but also to the Basin and Australia.
Not only does the site support a high level of species diversity, fish of the region also display a range in size at maturity from 40 millimetres, to more than 1 metre. They also possess contrasting body shapes, from benthic (bottom dwelling) flat fishes to pelagic species (fish that swim in the water column and are wider in the middle and taper toward the ends of their body). This biodisparity is another example of the high ecological value of the site.
In addition to a high level of biodiversity and biodisparity, the site also provides feeding areas, dispersal and migratory pathways, as well as the spawning sites that are so critical to its diverse fish population. The site is the only estuarine habitat for the MDB, and, as such, is the only access point for diadromous fish species within the Basin.
Diadromous species are those for which migration between freshwater and marine environments is required for the completion of their life cycle. Within the Coorong and Lakes, five species of diadromous fish can be found, including the Pouched lamprey, Shorthead lamprey, Common galaxias, Southern shortfin eel and Congolli.
The Murray barrages were constructed between 1935 and 1940 to keep salt water from entering the lower reaches of the River Murray system, as consumptive demand across the Basin increased. The barrages were not originally designed with fish passage in mind, and have hindered diadromous species from completing their life cycles. Water flowing swiftly through open barrage gates presents a physical barrier to the upstream migration of fish. Similarly, when closed, they create a barrier for fish to move between the MDB and the Coorong or the Southern Ocean.
Passage through the Murray mouth and the barrages is essential for facilitating the recruitment and sustaining populations of diadromous species. This is why environmental flows and fish passage are so critical to maintain the fish community and the site’s ecological character.
To address this issue, as part of a broader program to restore health to the pre-existing biodiversity of the Murray, the Murray-Darling Basin Authority (MDBA) implemented a program to reinstate fish passage along the River Murray from the sea to the Hume Dam. This saw the construction of fishways at 11 weirs along the river, together with fishways at Goolwa and Tauwitchere barrages, as well as on the mouth of Hunters Creek on Hindmarsh Island.
Building on the success of the program, six additional fishways are now being installed by the ‘Coorong, Lower Lakes and Murray Mouth Recovery’ project, funded by the Australian Government and the Government of South Australia, with the help and assistance of SA Water and the MDBA. Three fishways are now completed at Goolwa, Ewe Island barrage and Boundary Creek barrage,with the program to result in the construction of at least one fishway at each barrage by 2017, supporting the diadromous fish communities into the future.
Recent and previous fishway monitoring has shown how important and successful fishways, together with the provision of environmental flows, are in supporting diadromous fish populations. Monitoring has shown significant improvement in the site’s fish communities since the end of the Millennium drought.
This year has seen catches of Congolli and Common galaxias at historical highs, and this can be directly linked to the fishways and continuous flows through the barrages provided through environmental water. The delivery of water ensured connectivity between the Coorong and the Lakes was maintained.
Monitoring of the fishways during winter 2015 found an increase in Pouched lampreys moving through the barrages, with scientists from SARDI Aquatic Science tagging 55 fish with microchips to track their movement up the River Murray. Of the 55 tagged, 25 were tracked and recorded at fishways between Locks 1 and 11. One lamprey travelled a distance of 878 kilometres to Lock 11.
Not only are fishways important for maintaining connectivity, the provision of environmental water through the fishways and barrages is vital to support the broader ecology of the region. A recent study by the Goyder Institue in South Australia, highlighted the value of environmental water to estuarine productivity and food for fish predators like larger fish and waterbirds. The fishways not only provide passage, but also the opportunity to deliver modest environmental flows for longer to the Coorong, a result that is critical to maintaining the health of the site’s ecology, and which was not previously possible.
With the construction of the fishways at the Murray barrages and the ongoing provision of environmental flows through the Basin Plan, the ability to support the diverse fish communities of the region and therefore the MDB are well placed into the future.