Environmentalists are calling on the Tasmanian salmon industry to explain why more than 1,000 tonnes of salmon died in fish farms in Macquarie Harbour over seven months last spring and summer.
A government document published after a request by the Neighbours of Fish Farming, a group that campaigns against commercial salmon operations, suggest 1,150 tonnes of fish died in farms in the vast harbour on the state’s west coast between September and March.
The highest mortality rate was in January (314 tonnes) and December (266 tonnes). The group’s president, Peter George, said the figures suggested more than 10% of salmon stocks in the harbour had died, possibly due to overstocking and disease, which he described as a common issue in the industry.
“The actual causes need to be publicly disclosed,” George said. “As these mortalities have occurred in Macquarie Harbour, a public waterway, we need an explanation from the industry about what the hell is happening there.”
Luke Martin, the chief executive of the industry group Salmon Tasmania, said the figure was not related to the health of Macquarie Harbour, which has been under question due to the impact of fish farms on the Maugean skate, an endangered ancient ray-like species endemic to the area.
A group of some of Australia’s leading scientists this week urged the federal environment minister, Tanya Plibersek, to remove fish farms from the harbour to save the skate population, which fell sharply last decade as salmon stocks increased and dissolved oxygen (the amount of oxygen present in water) levels fell.
Martin said the state Environment Protection Authority had found conditions in the harbour were the best in more than a decade, and accused George of “muckraking” and “openly co-hosting events with the Greens”.
“Like all livestock farming, mortalities happen in our industry for many different reasons,” he said. “Mortality rates in Tasmania’s salmon farming industry are regularly reported to and publicly disclosed by the Tasmanian government under the strictest regimes applied to any farming sector.”
Guardian Australia asked Martin what would be considered a typical and reasonable mortality rate at salmon farms. He did not respond, but industry observers said 10% to 20% was a common figure internationally. In Scotland, it is 14.5%.
A Tasmanian government spokesperson said questions about typical livestock mortality rates should be directed to salmon companies. They said the industry was subject to a “comprehensive biosecurity program” and there were “routine reporting requirements” to ensure significant or sustained stock mortalities were reported to the chief veterinary officer and the EPA.
The Tasmanian Greens MP Vica Bayley said the number of mortalities was “enormous” and “most likely the result of overstocking and not environmental factors”. He said Macquarie Harbour carried only a fraction – about 13% – of the state’s salmon industry, suggesting the total number of “dead fish hauled out of our waters and dumped” would be far higher.
Bayley said the EPA chief, Wes Ford, had told a state parliament estimates hearing that there were 66 “elevated mortality” events at Tasmanian salmon farms last summer, but only seven were in Macquarie Harbour. A mortality event is when more than 0.25% of salmon die over three consecutive days.
Ford said the dead fish were dealt with by salmon companies in two ways: either through a Tassal rendering process facility, or treated with formic acid, turned into a liquid and spread over farmland. Some bodies went to landfill if the rendering facility was over capacity.
Bayley said: “We need the exact numbers of mortalities, we need to know what these poor animals are dying from and we need to know what effect this is having on our precious waterways and native wildlife.”
Plibersek is reconsidering the future of salmon farm licences in Macquarie Harbour after environment groups made a legal case alleging that an industry expansion in 2012 had not been properly approved.
In a letter on Monday, more than 30 scientists – including five fellows of the Australian Academy of Science and a past chair of the government’s threatened species scientific committee, Helene Marsh – encouraged Plibersek to revoke the licences to prevent the skate’s extinction.
The Guardian revealed in August that the threatened species committee had concluded fish farms were the greatest threat to the skate’s survival and suggested the industry should be either scaled back or removed from the harbour.
The reconsideration process has been criticised by the industry and the Tasmanian Liberal and Labor parties, which argue it is a threat to jobs at Strahan on the state’s sparsely populated west coast.
