The Marine Conservation Society (MSC) said it had removed mackerel, an oily fish packed with brain-boosting omega 3, from its latest version of its "fish to eat" list, and advised consumers to eat it less than once a week. The warning comes after the Marine Stewardship Council, which certifies fish stocks that are managed sustainably, suspended its certification of the north east Atlantic mackerel fishery.
Atlantic populations of mackerel have moved north-west into Icelandic and Faroe Islands waters, prompting their fishermen to take more stock than was previously agreed. Bernardette Clarke, fisheries officer at the MCS , said: "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. Negotiations to introduce new catch allowances have so far failed to reach agreement."
The conservation group said alternatives to mackerel were herring and sardine, and if people wanted to continue to buy mackerel, they should ensure it is as sustainable as possible – for example, fish caught locally using traditional methods.
Also removed from the "fish to eat" list is gurnard, because of a lack of data on population levels and concerns about how stocks of the increasingly popular fish are being managed.
Since gurnard has been historically caught as a "bycatch" by fishing vessels targeting other species, there are no catch restrictions – but if stocks are being increasingly targeted, they need to be managed sustainably, the MCS said.
The latest version of the "fish to eat" advises that herring stocks, coley and Dover sole from the English Channel are all in good supply, while whiting from the Celtic Sea also appears on the list for the first time. Farmed species are also given the green light to eat, including sturgeon caviar from closed fish farming systems, mussels, tiger prawns, Atlantic halibut and salmon and rainbow trout.
However, cod stocks from the North Sea remain below recommended levels. Ms Clarke said: "The importance of knowing what we are eat, as well as where and how it is caught, is essential to allow consumers to make the most sustainable choice."
The Scottish Fishermen's Federations aid the MCS had reacted "far too quickly and not taken into account the broader picture of mackerel stock science and ongoing research".
Ian Gatt, chief executive of the Scottish Pelagic Fishermen's Association, said: "There is a great deal of uncertainty in the current scientific advice."