Conservationists have expressed concern following the arrival of the world's second largest supertrawler off the Irish coast.

The 'Margiris' is capable of hauling up to 250 tonnes of fish per day.

The 142m vessel has been operating 50 miles off the Irish coast for the last week. Environmental and conservation groups have expressed their alarm and have called for a ban on such fishing activity due to the risks it poses to the sustainability of fish stocks and the wider marine environment.

The Dutch-owned vessel which is registered in Lithuania has been involved in a number of controversial incidents around the world.

It has been banned in Australian waters and last year found itself at the centre of an investigation by French authorities when a large "slick" of 100,000 dead fish, believed to have been discarded by-catch, was photographed near the vessel.

The supertrawler arrived in Irish waters earlier this week and has been slowly progressing north along the Irish coast. Its activity has been criticised by environmental and conservation groups such as the Irish Wildlife Trust, Fair Seas Ireland and Greenpeace.

Dr Kevin Flannery, a marine biologist who submitted a report on factory vessels operating of the Irish coast to the Department of the Marine in 2012, said the presence of such supertrawlers is having a devastating impact on the marine environment.

"This vessel tows a net the size of Croke Park hoovering up hundreds of tonnes of fish every day and nobody knows what it takes in. The size of these vessels and the lack of monitoring on board is a serious issue and a serious fault in the Common Fisheries Policy," said Dr Flannery.

"If it doesn't like the species, it simply dumps it at sea. On top of that there's a strong possibility of by-catches of marine mammals such dolphins, porpoises and small whales. Environmentally factory ships have to be monitored, they have to have observers on board," he added.

The Irish Sea Fisheries Protection Authority said it regards such large-scale pelagic freezer trawlers as posing "particular non-compliance risks." The agency said it is aware of the presence of the Margiris off the Irish coast and is closely monitoring its activity.

"The SFPA continues to monitor the activity of such vessels with the assistance of the Air Corps and the Naval Service. Under the Common Fisheries Policy, any vessel can fish in any EU waters where they have quota, apart from the territorial waters of an EU Member State," a statement said.

"We regard large-scale pelagic freezer trawlers, fishing in Irish EEZ but not landing into an Irish port, to pose particular non-compliance risks, and consequently we devote available resources in that direction. They also pose particular control challenges," the statement added.

Green Party MEP Grace O’Sullivan has called for an overhaul of EU fishing regulations, including a complete ban on such supertrawlers in EU waters.

"Very large industrial supertrawlers like this wipe out huge quantities of fish stocks, very often at the cost of the small-scale fishers. We should ban these large trawlers in all EU waters.

"There is a huge amount of subsidies given to these large operations like this. That is public money. I think subsidies should go it to genuine sustainable fisheries."

Ms O'Sullivan, who sits on the EU Fisheries Committee, said that there is an urgent need for new regulations to assist in the monitoring of supertrawlers. The committee is currently working on legislation that would allow for additional control mechanisms on supertrawlers, including remote electronic monitoring.

"There should be CCTV cameras on board so we can see the quantities of fish they are taking on board, the species of fish and also the by-catch because the by-catch is a huge issue."

The Dutch fishing giant, Parlevliet and Van der Plas, which operates the vessel has said the company has an excellent record for sustainable fishing and operates within its quota allocations.

It said accusations in relation to the levels of discarded by-catch are exaggerated and that the practice it engages in of mid-depth trawling rather than dragging a net across the seabed reduces the impact on the marine environment.