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ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.
The effects of a post-fire sediment “slug” on the fish fauna of the Ovens River, Victoria
Jarod Lyon and Justin O’Connor
Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, Victoria.
Email: Jarod.lyon@nre.vic.gov.au
Several extremely large fires have affected Victorian public land during the 2002/03 summer, burning approximately 1.08 million hectares of bush in the north-east and Gippsland areas of Victoria, as well as extensive areas of bush in southern NSW. The drastic effects of these fires on vegetation and terrestrial animal communities are often immediately apparent. However the effects on fish populations in and downstream from impacted areas may not be evident for many weeks or even months after the incident. On February 26th 2003, a flash flood occurred in a heavily burnt area of the upper Buckland Valley, causing large amounts of ash and sediment to be deposited into the Buckland River, a tributary of the Ovens River. This material quickly formed into a “slug”, which moved downstream through approximately 100 km of the most important Murray cod and trout cod habitat in Victoria. As well as lowering DO levels to below 0.2 ppm at any one point in the river for approximately 24 hours, the slug deposited huge amounts of fine sediment in its wake (a maximum of 18 000 mg/L suspended solids was recorded during the peak). Several fish species were found dead along the sides of the river, including Murray cod, trout cod, river blackfish, smelt, and carp. We surveyed Sustainable Rivers Audit (SRA) sites, previously surveyed 12 months before the slug, to determine the effects on fish populations. At sites in the upper sections of the affected area, a 100 % reduction in fish numbers was recorded. Further downstream, fish populations were progressively less affected by the immediate impacts of the slug, however huge sediment loads deposited in the river are expected to hinder spawning for several years.
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