Geikie Gorge fish deaths
Released 16 Dec 2015
Tests into the water conditions in the remote Geikie Gorge in Kimberley where dead fish were found last month indicate low oxygen levels as the most likely cause of death.
Department of Water Executive Director Regional Delivery and Regulation Paul Brown said the review of all the information gathered from the event indicated this was an event where the first rains after a dry spell had depleted oxygen in the water killing the fish.
The incident was initially reported by a local tour operator visiting the national park to the Department of Parks and Wildlife who initially attended the site to retrieve fish carcasses.
Scientists from Murdoch University’s Freshwater Fish Group and Fish Health Unit were contacted and responded as several of the dead Freshwater Sawfish and Bull Sharks were tagged as part of an ongoing research program. The Department of Fisheries also visited the site after receiving a call to FishWatch.
"This has happened on the cusp of the dry to wet season, and fish kills can often occur in conditions where rains wash organic matter into pools that are stagnant with low water levels and the resulting microbial activity uses up available oxygen causing fish deaths," Mr Brown said.
It is estimated that 12 Freshwater Sawfish, 9 Bull Sharks, a Freshwater Whipray, a catfish, numerous bivalves and Cherabin died over several days around 27 November 2015.
Mr Brown said the remote location, delays between the likely time of deaths and the discovery of bodies, and travel times required to respond meant fish samples were too decomposed for pathology testing.
"Observations from respondents noted the water was black, tannin stained, and likely to have carried large amounts of biologically active matter into the water where rapid bacterial decomposition occurred.
"Measurement of the oxygen levels in the water by Murdoch scientists support this, as do further observations that fish able to swim at the surface where the water is hotter but there is oxygen, such as barramundi, were not affected by the event.
Mr Brown said test results for algae toxic to fish conducted by the Department of Water did not indicate this as a likely cause, but that tests were limited by the conditions in which they were taken.
He said the response to the incident was greatly assisted by Murdoch University staff and students.
"We often rely on the first respondents in these incidents in remote areas, and the quicker the agencies are informed, the better quality evidence we can gather."
Contact with dead fish found in the wild should be avoided and the Department of Health advises against eating or handling of fish found in these circumstances, or fishing or recreating in waterways during a fish kill or algal bloom event.
People are asked to report any fish deaths to the Department of Fisheries FishWatch on 1800 815 507.
Algal blooms should be reported to ALGALWATCH 08 6250 8064 (office hours).
Contact: Peter Collins
Phone: 6364 6848