WHAT'S not to like about mackerel?

The humble scomber scombrus is cheap, healthy and even fashionable thanks to celebrity chefs from Jamie to Nigella, who have taught us to griddle it with a courgette and bean salad or bake it with fennel and pastis.

Above all it's plentiful – or so we used to think.

Earlier this year the Marine Conservation Society (MSC) downgraded mackerel in its list of fish to eat. On the MSC's traffic light system it went from green, showing it was sustainably fished, to amber, a sign that stocks are declining. Consumers were advised to eat mackerel "only occasionally".

The reason was simple. In recent years Icelandic and Faroese fishermen have taken advantage of a westwards migration of mackerel populations, possibly connected with climate change, to target the fish like never before. Encouraged by governments willing to ignore international concern and sign off ever-more generous quotas, they filled their nets with 300,000 tons last year, almost as much as the total permitted EU catch of just under 350,000 tons.

For the Scottish fishing industry this is fast becoming a disaster. Of the entire European quota, more than half is allocated to Britain and that effectively means Scotland: the vast bulk of our mackerel is caught by 25 boats registered in Fraserburgh, Peterhead and Lerwick. It is the industry's most valuable catch, worth £164m in 2011, or one-third of all the fish landed.

The response of Scottish fishermen to the Marine Conservation Society has been diplomatic. The MCS's warning is unnecessary, they say. Mackerel stocks remain healthy. We should carry on enjoying our affordable super-food, is the message. But their furious attack on the Icelanders and Faroese shows how seriously they are taking the long-term threat. "A mugging job" is how the Scottish Fishermen's Federation describe their rivals' actions.

The dispute has been escalating for three years. Ministers and officials from the EU, Norway, Iceland and the Faroes, who jointly manage fishery, have met 12 times already but failed to reach a compromise. The EU has agreed sanctions – including a ban on landing Icelandic mackerel in European ports – but has not yet imposed them. The Icelanders and Faroese, meanwhile, accuse the EU of trying to freeze them out of a fair share of the fish in their waters.

The longer the stalemate persists, the worse it is for the Scottish fishing industry and the communities it supports. That's why Rural Affairs Secretary Richard Lochhead's constructive proposal yesterday for a neutral mediator to be appointed makes sense. With both sides so deeply entrenched an impartial figure, acceptable to all, may have the best chance of breaking the impasse. If the Icelanders and Faroese are genuinely willing to accept a fair quota, as they claim, they should accept the idea too.

It is to be hoped agreement can be found. It would be a tragedy for consumers and the hard-pressed Scottish fishing industry alike if mackerel goes the same way as cod, once so abundant it was as cheap as its good friend the chip but now a luxury thanks to decades of overfishing.