The 22-year-old from Slovakia was reported missing yesterday morning from the Fehn Sirius, which was en route from Belfast to Portugal, as it headed past Arklow, Co Wicklow.
According to The Irish Times, he was last seen on the cargo ship around 10pm on Monday night as it headed south of the entrance to Strangford Lough.
Lifeboats from Portaferry and Newcastle in Northern Ireland and Arklow joined the search and rescue operation, which was assisted by the RAF helicopter based at Prestwick in Scotland and an Irish Coast Guard helicopter.
However, most rescue services have now been stood down as the Fehn Sirius continues to backtrack in the Irish Sea, with assistance from the Naval Service vessel LE Ciara.
Only three days ago the body of another mariner was recovered from the Irish Sea off the north Dublin coast, more than a month after he went missing.