The ‘Cane Toad of Fish’ has been discovered in the Vasse-Wonnerup Estuary, following the first quantitative fish surveys in the area conducted by researchers from Murdoch University.
The mosquitofish (Gambusia holbrooki) has become widespread since its introduction to Australia in the 1920s, threatening native species due to its aggressive nature and feeding on eggs and larvae of native fish and frogs.
However, just as concerning is the discovery of another well known feral fish species, the goldfish (Carassius auratus) in the Vasse Estuary.
Often flushed down the toilet or released into waterways as an unwanted pet, goldfish love conditions in the rivers of South-Western Australia and can grow up to 40 cm in length and weigh over two kilograms!
Their vigorous feeding activities uproot vegetation, silt up waterways and enhance algal blooms. With goldfish present in the Vasse Estuary, there is concern that they may spread into the Sabina, Abba and Ludlow Rivers as well as the Wonnerup Estuary.
Murdoch University researcher Dr James Tweedley led the study carried out in January this year, and will be highlighting the results of this and other recent surveys in the ecologically significant wetland system at a free presentation evening on Thursday, August 16 at Abbey Beach Resort from 6.30pm.
“Apart from the discovery of the two feral fish, our studies also discovered an extremely high density of fish compared to other estuaries in the South-West. For example, in the Vasse and Wonnerup Estuaries the average number of fish recorded exceeded 780 fish per 100 m2 compared to the 169 fish per 100 m2 documented in a similar survey in the Leschenault Estuary,” said Dr Tweedley.
Dr Stephen Beatty and Associate Professor Alan Lymbery, also from Murdoch University, will provide information on the subsequent feral fish control program which is removing goldfish and mosquitofish from the Vasse-Wonnerup Estuaries and tributary rivers.
Other information presented will include an overview of the native and introduced freshwater and estuarine fishes in South-Western Australia. It will also cover the latest known distributions and impacts of introduced fishes of Western Australia aquatic systems with a focus on the South-West region.
This project is supported by the South West Catchments Council, Geocatch and Murdoch University through funding from the Australian Government’s Caring for our Country and the Government of Western Australia.