Abandonned Cage Sites Show No Recovery After Two Years


JULY 18, 2014

Abandoned location in harbour shows no recovery after two years, scientist says

SHELBURNE - Two years after an aquaculture company's salmon pen location in Shelburne Harbour was abandoned, part of the harbour bottom is still dead, an independent study has revealed.

Inka Milewski, a marine biologist who currently serves as the science adviser for the Conservation Council of New Brunswick, has been studying selected areas of the Shelburne harbour bottom since 2011.

"It's not a good news story, because we don't have recovery," Milewski said this week in Shelburne.

She studied a lease site off Sandy Point where a salmon cage had held fish. The lease site was surrendered back to the province in 2011, Milewski said.

The site was held for several years before that.

No new cages are operating off Sandy Point, but other parts of Shelburne harbour have cages.

The Canadian Council of Ministers of the Environment has established sediment quality guidelines across the country for marine and fresh water.

Milewski said her findings show guidelines have been exceeded.

There's an assumption, she said, "that if you fallow a site for six to 12 months, ... that that will be sufficient time for recovery of the sea bottom."

But on what do industry and government base this assumption?

"That's a good question," Milewski said.

Maybe they measure sulphide levels in bottom goop, she said.

"The amount of sulphides in the sediment is a function of the amount of organic material in the sediment," said Milewski.

"The Nova Scotia government wants farm sites to maintain a level of sulphides in the sediments that are below 1,500 micro-molars of sulphide," she said, using the unit of measure for sulphides.

A farm that begins to exceed that level would have to take action by either having fewer fish or moving the fish to a new site, she said. "They got as high as 11,000 before the (site) was eventually abandoned," Milewski said about sulphide levels.

"It's the organic material, primarily the feces of the fish and the uneaten food that settles on the bottom and begins this decomposition process, that results in the production of these sulphides."

Copper and zinc were also found in bottom sludge at higher levels than expected.

Feed is a probable source and some netting is likely treated with a copper-based solution to help prevent seaweed from growing on the ropes and gear, Milewski said.

"The farm is likely the source of these high copper levels," she said.

The metals may inhibit organisms like some marine worms from coming in and helping to break down the sulphides, which also remain high, she suggested.

Jon Grant, the NSERC-Cooke industrial research chair in sustainable aquaculture at Dalhousie University, is also studying the area. Some of his students were there last week collecting samples.

"We're doing some work there," Grant said Friday.

The site has not recovered readily, he said.

"It does seem to be a little bit exceptional," Grant said. "The question is, if it has not received new material, why hasn't it recovered?

"I think it has to do with the sulphate chemistry," he said about a residual component left behind by the fish pen.

"Metals don't decompose but industrial sites that have been harder hit by metals have recovered."

Milewski said her studies cost about $10,000 per year.

She receives funding from foundations for grant proposals and has shared her results with the provincial Department of Fisheries and Aquaculture.

A department spokeswoman said you just can't with certainty say how long it will take for an area to fully recover.

"We have to review the study," department spokeswoman Krista Higdon said in an email.

The information it contains will be considered as the government develops new regulations for a sustainable and environmentally friendly aquaculture industry in Nova Scotia, she said.

Government also continues to monitor the site in Milewski's study, "which indicates a positive recovery trend," said Higdon.

"Recovery time is site-specific. We do not put a time frame on site recovery."

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