EXPERTS have responded to the rising popularity of calamari as the "prawn cocktail of the 21st century" with new information on whether it is sustainable.

Calamari - also known as the humble squid - is now appearing on the menus of many popular chain restaurants, prompting the Marine Conservation Society to increase the number of ratings for the seafood as part of its Good Fish Guide.

There is little information for squid fisheries, according to the wildlife charity, with the seafood in the north-east Atlantic classified as a non-pressure species so no assessments of stock have been carried out.

But with more imports and a growing number of queries about the seafood, the MCS has provided ratings for some of the more commercial fisheries, with more new ratings set to published at the beginning of 2017.

Japanese flying squid is on the "fish to eat" list, owing to the way it is caught, but heavily fished species caught in the Pacific or off Argentina should only be eaten very occasionally, the MCS said.

The MCS said squid stocks were thought to be as much affected by environmental pressures as fishing, but fisheries still needed to be well managed while the effects of industrial fishing of squid on ocean food webs were unclear.

Squid are caught by "jigging", which uses a jig or grappling hook on a line which is jerked in the water to snag the fish, usually at night using the aid of lures or light attraction. It can be done on an industrial scale.

Elsewhere, fishing vessels trawl the open ocean to catch squid using big "purse seine" nets on an industrial scale, often using small meshes which can catch protected species such as sharks, marine mammals and turtles, as well as other fish.

The advice from the MCS is to choose squid from fisheries using low-impact methods of small-scale jigging, such as the fishery in Sennen Cove, Cornwall, where fishermen go out in punts.

Among imported squid, Japanese flying squid scored a "two" in the one to five rating system.

Bernadette Clarke, MCS Good Fish Guide manager, said: "This is generally due to the highly selective and low-impact fishing method known as jigging used in the fishery and the fact that stock assessment has been carried out.

"There is also a low vulnerability score for the species and management measures are applied in the fishery.

"On the other hand, we have given both Humboldt or Jumbo squid, jigged in the East Central Pacific, and Argentine short fin squid, caught by purse seine or by jigging method in waters off Argentina and the Falklands a "four" which means it's not as sustainable and should be eaten only very, very occasionally."

She said the two species were the most heavily fished squid in the world and, because fishing took place on the high seas, management of the fisheries were complicated by illegal, unreported, unregulated fishing.

Elsewhere in the Good Fish Guide listings, cod caught in the Celtic Sea and the Kattegat - an area forming part of the connection between the Baltic and North Sea - have come off the red list with a rating upgrade from five to four.

Mackerel from fisheries which have been newly certified by the Marine Stewardship Council as sustainable are back on the fish to eat list.

But there is bad news for plaice, especially if it has been caught in the Irish Sea using a form of trawling the bottom of the sea known as demersal otter trawl which now has a "five" rating and is one to avoid.