Good and bad of harbour report

OXYGEN levels in salmonfarming hotspot Macquarie Harbour have partially improved but concerns remain about the number of animal species in some areas of the waterway, new research has found.

Institute for Marine and Antarctic Studies researchers yesterday released the latest results of ongoing surveys of environmental conditions in Macquarie Harbour.

The report provides an up- date on the status of oxygen dissolved into the water and benthic (bottom water) conditions in the harbour. It follows previous reports released in January, May and September 2017, and January this year.

IMAS research fellow Jeff Ross, who leads the research project, said the report showed improved dissolved oxygen levels in middle and bottom waters of the harbour as a result of oxygen “recharge events” caused by favourable weather conditions and lower river flows over the past eight months.

“These improvements in [dissolved oxygen] were most notable in early November 2017 and January and March this year as strong northwesterly winds and lower river flows resulted in more oxygen being mixed into the water column,” Dr Ross said.

However, Dr Ross said the report showed little change from the low levels of faunal abundance and numbers of benthic species recorded in the deeper central area of the harbour from the January 2018 survey.

“Following the sustained period of [dissolved oxygen] recharge over summer and early autumn it will be important to see whether there is a return to higher faunal abundances and number of species recorded in our next surveys this winter,” he said.

“Ultimately … sustained faunal recovery in the deeper central region of the harbour will most likely depend on the return of more stable and higher [dissolved oxygen] concentrations in mid-bottom waters throughout this year.”

CLAIMS that hundreds of thousands of Atlantic salmon have died from disease at Tasmanian aquaculture sites have been dismissed by fish-farmer Tassal.

In State Parliament yesterday, Greens MP Rosalie Woodruff asked Primary Industries Minister Sarah Courtney and Environment Minister Elise Archer whether the industry was expanding too fast for regulation to keep pace.

“We have received reports of a recent devastating outbreak of the pilchard orthomyxovirus in Tassal’s pens at Tasman and Dover, the same virus that has dogged operations in Macquarie Harbour,” she said.

“Allegedly, the Tasman operation is losing around 1200 fish a day and so far, allegedly, have lost 300,000 salmon to the disease.

“There are serious questions being asked about the amount of chemicals being used to try to control the outbreak, with impacts on worker’s safety, fish health and marine ecosystems being posed.”

In lengthy answers, neither minister disclosed any knowledge of such a mass diseasedeath event, but nor did they deny it.

A Tassal spokesman said the company was not affected by high fish mortality.

“POMV is naturally occurring and it is endemic throughout all Tasmania. All salmon farmers deal with it from time to time,” he said.

“Current levels are the lowest they have been for the past three years due to good fish husbandry practices and risk mitigation measures.

“We are expecting good growth and harvest volumes for the current year — more than last year — because of the way we have managed POMV and fish husbandry practices in the past.”

A Huon Aquaculture spokeswoman said the company did not farm in those areas. Neither firm has reported any loss of fish to the Australian Stock Exchange since Tassal responded to claims of 1.35 million fish lost to POMV in Macquarie Harbour in May.

Labor Primary Industry spokesman Shane Broad said disease outbreaks had the potential to wipe out the industry and a biosecurity plan was needed.

“International experience from every major salmon region demonstrates that viral infections in the orthomyxo virus family lead to industry collapse,” Mr Broad said.

“Is Sarah Courtney waiting for the industry to collapse before she takes action?”

In May, the Greens’ claims that 300,000 fish had escaped from aquaculture pens during a storm were roundly ridiculed by the industry, despite an extended bumper catch subsequently being reported for the state’s fishers.