Pete Bevington

9 January, 2009

A MAJOR outbreak of the sea lice parasite amongst caged salmon off Shetland’s west coast led government inspectors to detect a deadly virus on a site there last week, it has emerged.

Yesterday (Thursday) the Scottish government’s Fisheries Research Service said they had used new powers to investigate sea lice problems when inspecting the Scottish Sea Farms site east of Hildasay, west of Scalloway, where Infectious Salmon Anaemia (ISA) was found.

Reports of a major sea lice infestation off the south west coast of Shetland were confirmed when Shetland’s largest salmon producer, Hjaltland Seafarms, owned by Norwegian company Grieg Seafoods, reported “extraordinary high mortality … as consequence of biological issues (sea lice)”.

Shetland Islands Council meanwhile confirmed that its landfill site had received 1,300 tonnes of dead salmon from across the isles for disposal, between October and December, a figure “a lot higher” than in previous months.

Inspectors turned up at the infected site east of Hildasay to investigate two reports of serious problems with sea lice and were surprised when tests revealed the presence of the highly infectious ISA virus.

ISA last struck in Scotland ten years ago, costing the industry £100 million and 200 jobs. The source was never discovered, though it was widely blamed on a well boat carrying the disease from site to site.

Yesterday Charles Allan, group leader of the Aberdeen-based Fish Health Inspectorate, said it would be “very unusual” for sea lice to be the source of the ISA in Shetland.

“What is far more relevant is that sea lice infestations are stressful and we do know that increased stress levels in fish will leave them more open to infections, just like if you have been working hard and are permanently tired you are more likely to get a cold,” Mr Allan said.

He said they had inspected the site east of Hildasay to check up on sea lice problems following contact with Scottish Sea Farms and another “non attributable” source.

While the fish had appeared “moribund” and “not very well”, none of the clinical signs normally associated with ISA were evident, so the virus has not yet been blamed for any fish deaths.

Mr Allan added that they might never find “a definitive source” of the infection, and his team’s job was “to contain and eradicate”.

The fact sea lice have been a major problem in Shetland was highlighted by a report to the Oslo stock exchange by the Norwegian owners of Shetland’s biggest salmon producer Hjaltland Seafarms, who have cages near the infected site.

Bergen-based Grieg Seafoods told the Oslo Børs: “Extraordinary high mortality in the Shetlands (UK) as a consequence of biological issues (sea lice) has caused extraordinary write downs.”

Overall harvest in the fourth quarter was down 2,500 tonnes on the previous three months, predominantly because of the Shetland problem.

Last night no one from Hjaltland Seafarms or Scottish Sea Farms, which is also Norwegian-owned, could be contacted.

David Sandison, of the trades body Shetland Aquaculture, said he could not comment on the scale of the sea lice problem in Shetland in recent months, but admitted it had got worse of late.

“Control of sea lice is the biggest problem the industry faces. We have not had a situation for several years where we have had a large scale challenge, but the last year was very challenging for sea lice,” he said.

ISA was detected in fish from just one site, which has since been harvested and will remain fallow. There is no evidence the disease has spread beyond this site, but two nearby SSF cages are under suspicion of carrying the disease and are also now clear of fish.

Strict movement controls have been enforced within a control zone containing 11 cages and a wider surveillance zone with 31 cages, all of which will have been inspected by today. Only 11 of these cages actually hold salmon.

Three companies have cages within the control zone – Scottish Sea Farms, Hjaltland Seafarms and Skelda Salmon Farms. The Scalloway-based NAFC Marine Centre and Shetland Halibut Company also have cages in the surveillance zone, one of the densest fish farming areas in Shetland waters.

It is likely to be some weeks before inspectors can give a verdict on how widespread the ISA problem is.

Mr Sandison said local firms had been planning to leave cages empty in this area prior to introducing a new management regime, where everyone was growing the same generation of fish. Similar moves were made 10 years ago after the last ISA outbreak.

“The big immediate hope is that (ISA) is contained to this one area. When we know that’s the case then we have to make sure the controls are in place and as effective as possible.”