The number of migrant deaths in the Mediterranean, a sea with many busy shipping lanes where international law and centuries of custom oblige ships to assist those in need, is shocking.

The United Nations High Commissioner for Refugees (UNHCR) estimates that 1,500 people died in the Mediterranean in 2011 alone, making it the deadliest year on record. Fortress Europe, an internet blog that tracks deaths of those seeking to reach Europe, puts the number at over 2,000. The real number may be even higher.