Saleh Saeed Nasser has been patrolling Yemen’s coastline for 15 years. For most of his career, he’s seen migrants arrive on the pristine shores of Shabwa province from the Horn of Africa. But in recent years, as his country's three-year civil war has brought on terrorism and the world's worst humanitarian crisis, something counterintuitive has started happening: More migrants from Africa are rushing to shore and overwhelming the coastline he patrols as a member of the country’s Coast Guard. More than 87,000 migrants arrived last year alone.