THREE of the country's biggest supermarket chains are refusing to buy Scottish mackerel – a catch worth about £160 million a year to Scotland's economy.

Sainsbury's, Marks & Spencer and The Co-op say they will not buy Scottish mackerel while its environmental certification is suspended because of a dispute with Iceland and the Faroe Islands.

The decision has prompted a fierce political row, with Scottish ministers under fire for failing to engage with retailers. The fishing industry said it would be "extremely disappointed" if the supermarkets abandoned Scottish mackerel.

The mackerel catch is by far the most valuable of all Scottish fish, with the 146,000 tonnes landed in 2011 worth £163 million. But it has become caught up in an international crisis that is not of Scotland's making.

The crisis was sparked by Iceland and the Faroe Islands breaching the quotas agreed by scientists for mackerel in the northeast Atlantic. Overfishing by the two countries has led to the quotas being exceeded by 25% in the last two years.

As a result, the Marine Stewardship Council (MSC), which certifies that fishing is sustainable, has suspended certification of the entire mackerel fishery. Now, an investigation by the Sunday Herald has discovered this has persuaded Sainsbury's, Marks & Spencer and The Co-op to shelve plans to buy Scottish mackerel.

"In light of the MSC's decision to remove certification, and in line with our own sustainable sourcing policies, we have taken the decision to stop sourcing from the affected fisheries pending an agreement between the parties involved," said a spokeswoman for Sainsbury's.

Marks & Spencer said it would not buy Scottish mackerel unless it was certified by the MSC. "Ensuring all of the fish we sell is from sustainable sources is at the heart of our business," said a company spokeswoman.

The Co-op said that it was "working with our suppliers to find alternatives sources", though it hoped the situation would be resolved before it had to replenish its mackerel stocks. The three retailers said they would still sell mackerel that was caught before the certification was suspended.

However, other supermarkets canvassed by the Sunday Herald said they would buy Scottish mackerel, even without an MSC certification. Tesco said it had no current plans to change its suppliers for mackerel, and Aldi plans to continue offering the same products. Waitrose and Morrisons also said they had no plans to stop selling Scottish mackerel.

According to Labour's shadow environment secretary, Claire Baker, such supermarket confusion was unfair on consumers. "Many will feel caught between wanting to do the right thing in terms of sustainability and supporting the Scottish fishing fleet, which has done nothing wrong," she said.

She accused the Scottish Government of "a woeful lack of engagement with supermarkets". She called on ministers "to urgently engage with retailers in Scotland to make sure consumers and the mackerel fishing fleet can come through this difficult time as painlessly as possible."

But Fisheries Secretary Richard Lochhead responded by saying he needed no lectures on the need to talk to supermarkets. "I have personally raised my concerns over their sourcing of seafood on many occasions," he said.

"Scotland's priority is to have an international deal in place between all parties that protects the sustainability of the mackerel stock – but not at any price."

Ian Gatt, the chief executive of the Scottish Pelagic Fishermen's Association, argued it would be unfair to penalise Scottish fishing boats for a problem they did not cause. "I'd be extremely disappointed if consumers in Scotland can't buy Scottish mackerel," he said.

"The stocks are still high enough for supermarkets to put Scottish mackerel on their shelves."