The UNHCR said another 71 people - from Somalia and Ethiopia - were missing after Thursday's incident.
Some of the 293 survivors said the smugglers ordered some 450 migrants to jump when their boats hit rough seas near the coast town of Ras al-Kalb.
They said those who refused to jump were stabbed and beaten with clubs.
"We are horrified by this latest tragedy," said UNHCR's Assistant High Commissioner Erika Feller after returning from a visit to Yemen.
"These brutal smugglers care nothing about the fate of the people they prey upon, both refugees and... migrants who are desperate to escape persecution, violence and poverty in the Horn of Africa," Ms Feller said.
'Attacked by sharks'
Some of the 293 survivors said four smugglers' boats approached the Yemeni coastline on Thursday morning in rough seas and strong currents.
They said the passengers were then ordered to jump into the sea.
Some of the migrants were attacked by sharks, and several recovered bodies showed signs of severe mutilation, the survivors said.
The incident is the latest in a series of tragedies involving smugglers' boats carrying people across the Gulf of Aden from Somalia.
It brings the total number of dead and missing so far this year in Yemen to 262, the UNHCR said.
Some 27,000 people made the crossing from Somalia in 2006, but 330 others died and 300 went missing, according to the UN agency.The town of Boosaaso is the main point of departure for people fleeing Somalia.