[Belongings of dead migrants, which were recovered by the Libyan coast guard, are seen after their boat sank off the coastal town of Zuwara, west of Tripoli]By Aidan Lewis and Ahmed Elumami TRIPOLI (Reuters) - After a flurry of boat departures that sent hundreds of migrants to their deaths in the Mediterranean, survivors told police they had been kept for weeks on one meal a day in holding houses near the Libyan shore. As calmer summer weather begins, European officials who struck a deal with Turkey to block crossings to Greece have been scrambling for ways to shut down flows on the other major sea route into the EU from Libya.