ZIPPING across the choppy Aegean in his powerboat, Nassos Karakitsos, a volunteer with a search-and-rescue NGO called Emergency Response Centre International, scans the horizon for refugees. He spots none. A few months ago the seas around the Greek island of Lesbos were filled with overstuffed rubber dinghies (“balloons with engines”, Mr Karakitsos calls them) carrying Afghans, Iraqis and Syrians from the Turkish coast. Today they are home only to the more forbidding vessels of the Greek coast guard, Frontex (the European Union’s border agency) and NATO, lately arrived to help with maritime surveillance. The quiet seas are the result of a deal struck between the EU and Turkey to reduce migrant flows, which came into effect on March 20th. It took everyone by surprise, says a European official on Lesbos, and there were teething troubles: the police tailed a Turkish liaison officer stationed on the island, suspecting he was a spy. But for now the migrants have stopped coming. Some of the scrappy volunteer groups that flocked to Lesbos last autumn, when 6,000 refugees might clamber ashore in one day, are closing shop. Larger organisations are moving...