Iceland has been accused of taking an excessively large share of mackerel from the sea, despite its decision to cut its quota for the year.
The North Atlantic country has announced it will reduce the amount of mackerel it takes in 2013 by 15%, the Scottish Government said. But ministers and fishing industry bodies said the stock continued to be damaged and they called for further action to manage it in a sustainable way.
The Faroe Islands and Iceland have both set themselves large quotas of mackerel in recent years, prompted by Atlantic populations of mackerel moving further north west into their waters. Their stance has provoked an ongoing dispute with other countries that target the fish.
Responding to Iceland's decision to cut its quota, Fisheries Secretary Richard Lochhead said: "It is disappointing that Iceland remains intent on taking an excessively large share of the TAC (Total Allowable Catch), a greater share than Scotland, despite their short history in the fishery.
"This will continue to damage our most valuable stock and an opportunity has been missed to show willingness to help bring this dispute to end. It is now clear that further steps have to be taken to manage this stock in a sustainable manner.
"I believe that the best way this can be achieved is by the appointment of an independent mediator who can facilitate co-operation in an objective and neutral manner. I am also calling on the EU (European Union) to deliver on promised action."
Ian Gatt, chief executive of the Scottish Pelagic Fishermen's Association, said: "Whilst Iceland is following the lead of the EU and Norway who have already reduced their mackerel quota by 15%, it is an inescapable fact that Iceland is still taking an excessively large share that is fished unilaterally and outwith any international management plan."
Mackerel is worth millions each year to the Scottish economy and is the fleet's most valuable stock. Last month, conservationists warned that mackerel is no longer a sustainable choice for a regular fish supper, in the face of overfishing of the stock.
The Marine Conservation Society (MCS) said it had removed mackerel, an oily fish packed with omega 3, from its latest version of its "fish to eat" list and it should be eaten only occasionally.
Bernadette Clarke, fisheries officer at the MCS, said at the time: "The stock has moved into Icelandic and Faroese waters, probably following their prey of small fish, crustaceans and squid. As a result, both countries have begun to fish more mackerel than was previously agreed. The total catch is now far in excess of what has been scientifically recommended and previously agreed upon by all participating countries."