Fishery takes on sea lice without drugs
‘Hydrolicer’ pulls salmon into tank, then pressurized water dislodges parasites
Marine Harvest Canada Inc. says it has successfully treated fish in a net-pen Atlantic salmon farm near Campbell River with a drug-free, chemical-free method for controlling sea lice.
A “hydrolicer” barge pulls fish from the pens into a tank where it uses pressurized water to dislodge sea lice. The pests then are collected by filters for disposal, according to company spokesman Jeremy Dunn.
“Our veterinarians and operations people say the treatment went very well and so it is now part of our integrated pest-management system,” he said. “It’s the first time the hydrolicer has been used on the West Coast.”
B.C.’s fish farmers are keen to reduce their reliance on drug-based treatment, after DFO confirmed resistance to the feed-based treatment Slice, in sea lice taken from Cermaq’s Bawden farm in Clayoquot Sound earlier this year.
The unit is most effective on fish through the middle of their growth cycle, Dunn said. “It doesn’t work on very big fish and it doesn’t work on very small fish.”
Having a drug- and chemicalfree treatment option will help the company meet the requirements of the Aquaculture Stewardship Council, which certifies farms for environmental performance and sustainability, he said.
A recent report from SeaChoice noted that about half of B.C.’s ASC-certified farms have difficulty meeting the certifier’s sea-lice thresholds.
Since 2009, salmon farmers such as Marine Harvest and Cermaq relied on the drug in Slice for sea-lice control.
Since 2013, companies have been able to apply to Fisheries and Oceans Canada (DFO) to use hydrogen peroxide baths when Slice is ineffective.
“The hydrolicer is now the third tool we have and in January we expected to receive our freshwater well boat, which is our fourth tool,” said Dunn.
The 75-metre well boat draws fish into a tank equipped with a desalinator.
Sea lice die after a few hours in fresh water.
“We can use that same vessel for (contained) peroxide treatments,” he said.
Cermaq will take delivery of its own $12-million, custom-built hydrolicer early in 2019, the Canadian operation’s biggest ever capital investment.
“We need plan B, C and D, so we can mix up our approach and avoid being reliant on treatments that can lead to resistance,” said Linda Sams, sustainable development director for Cermaq Canada.
Cermaq Norway also began testing on a new semi-closed containment farm design in Norway late in September, said David Kiemele, managing director of Canadian operations.
The pens, made from a flexible composite, cost four to six times as much as traditional net pens and cost about 10 per cent more to operate, due to higher energy requirements.
The farm pumps water from a depth of 13 metres — well below where sea lice larvae lurk — to prevent sea-lice infestations.
Cermaq is working with DFO and the provincial government to approve the design so it can begin trials here in Canada.
“If it reduces our treatment costs, it’s a business case we are prepared to make,” said Kiemele.
Resistance to Slice was documented by DFO in farms at Klemtu in 2013, in Esperanza Inlet in 2017 and again this year in Clayoquot.
Lice from Klemtu showed a genetic signature for Slice resistance seen in other fish-farming regions, said DFO biologist Simon Jones, who specializes in parasites.
Marine Harvest reduced Slice applications and implemented hydrogen peroxide treatments at the Klemtu farms, which are operated in partnership with the Kitasoo/ Xai’xais First Nation.
Researchers found that two years after the initial outbreak, Slice resistance began to fade away, said Jones.
This year’s sea-lice infestations at Clayoquot affected seven of Cermaq’s 14 farms in the area and one, the Fortune Channel farm, will be shuttered for a full year.
Ocean conditions were noticeably different at the Clayoquot farms as early as November, said Sams.
When the company began Slice treatments in response to elevated sea-lice counts in January, there were signs of “increasing resistance,” she said.
They followed up with peroxide treatments using a well boat supplied by Grieg Seafood.
The company harvested fish early to depopulate some farms. The fish from Fortune Channel also had damaged gills due to plankton and algae blooms and were destroyed rather than subjected to further treatment.
Wild salmon tend to spread sea lice to fish farms when they return from the ocean in the fall, said Jones.
After that, local salinity and water temperature as well as the number of active farms in a given area are factors in how successfully lice spread inside the farms, he said.
Relatively low rainfall last winter led to higher than normal salinity in Clayoquot, rather than the usual cycle of low salinity that naturally suppresses sea lice.
If sea lice are not well-controlled on the farms by spring, they can spread to wild, juvenile salmon as they migrate from our rivers into the ocean.
Sea lice can harm or kill juvenile salmon.
Most years, about 90 per cent of farms are below the treatment threshold of three motile sea lice per fish during the wild salmon out-migration period between March 1 and June 30, according to DFO.
“The Clayoquot farms exceeded that threshold by an awful lot,” said Jones.
“There may be areas of the coast that are more prone to see resistance developing, so we need to look at that more closely.”
The treatment failures at Cermaq farms in Clayoquot are still under investigation by DFO.