Fish farming. Picture: 123RF/NADOTCHIY
Fish farming. Picture: 123RF/NADOTCHIY

Sydney — The salmon farms in the far south of Australia, where icy winds roar in from Antarctica, seem an unlikely casualty of global warming. But as tropical waters flow further south, ocean temperatures are rising even around the island state of Tasmania — stressing fish and stunting their growth.

That’s prompting companies such as Huon Aquaculture Group  and Tassal Group to find new ways to mitigate the impact of climate change.

Both belong to an industry and government partnership that’s selectively breeding fish to tolerate the warmer waters. Huon is experimenting with “fortress pens” to withstand mild weather so it can farm further offshore where the water is colder. It’s a further sign that agriculture in all its forms must adapt to survive human-induced climate change — from breeding heat-tolerant cattle in Florida to growing salt-resistant crops in Egypt.

While Australia represents only about 2% of worldwide salmon production, the nation is providing valuable lessons to a global industry worth $15.4b. Huon’s pen designs are being studied by salmon producers as far away as Norway and Chile, according to deputy CEO Philip Wiese.

“There’s a lot of interest in this technology,” said Wiese. “People like coming to visit us because we are on the forefront of change in the industry.”

Warmer waters

Tasmania’s salmon farmers are facing a serious problem. Surface waters have warmed by 2ºC in the past 60 years, and will rise another 3ºC in the next half-century as a tropical current running down Australia’s east coast brings warm water to the deep south, according to government forecasts.

Marine heatwaves that have stunted fish growth in two of the past five years will become more prevalent, government scientists say.

UN report on oceans

The salmon industry’s selective-breeding programme, overseen by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), is having some success.

The programme has improved growth rates and tolerance to amoebic gill disease by more than 10% in every three-year breeding cycle since it began in 2004

Waters in a test hatchery are warmed to see which fish thrive despite the stressful environment, and they’re sent to farmers’ test pens. DNA samples of fish that grew more, and had a higher tolerance to a disease that’s prolific in farmed salmon, are sent back to the hatchery. Those families are then selected for commercial production.

The programme has improved growth rates and tolerance to amoebic gill disease by more than 10% in every three-year breeding cycle since it began in 2004, according to the CSIRO.

Salmon farmers are also shifting production from sheltered inlets to further offshore. That’s partly being driven by the state environment regulator halving the production cap in Macquarie Harbour on Tasmania’s west coast to prevent the estuary from collapsing from over-farming.

Concerns about the environmental impact of intensive salmon farming have spurred a campaign by community groups and commercial and recreational fishers against the companies. Campaigners at the Tasmanian Alliance for Marine Protection (Tamp) non-profit organisation want an immediate halt to the expansion offshore until the impacts on wild fisheries are known.

They complain that debris from the farms clutters waterways and shorelines and that fish waste alters the biodiversity of areas. Tassal and Huon say they’re creating local jobs and are environmentally responsible.

The shift offshore is also prompted by the search for cooler waters. And it’s a risky move.

Damaging storms

Work can’t be done in harsh weather and pens can be destroyed by violent storms. Huon lost 120,000 fish last year when 6m  waves and wind gusts in excess of 100km/h from the Southern Ocean tore through the aptly named Storm Bay.

Huon spent two years developing a twin-net pen, at a price of A$1m a piece, to withstand the weather and keep seals out. Moorings help anchor an outer predator net as far as 7m from the inner net, which contains the fish. The company said it’s working with global equipment suppliers to export the technology to Norway and Chile.

Tassal, which also has a lease in Storm Bay, is developing “sanctuary” pens to keep seals out. The company, Australia’s largest salmon producer, is also investigating farming off King Island in the Bass Strait, a notoriously rough stretch of water, according to its 2018 sustainability report. The company didn’t respond to requests for comment.

The climate mitigation efforts appear to be working. Tassal sees gradual growth in salmon production from about 33,000 tonnes last financial year, according to company filings. Huon expects production to climb almost 60% in the next two years from just less than 19,000 tonnes in the 12 months ended June 30.

It’ll only happen if the fish aren’t stressed, said Wiese. “Happy fish, happy customers.”

Bloomberg