Up to 50 young migrants were "deliberately drowned" by a people smuggler who chose to sacrifice their lives rather than risk arrest, the UN's migration agency said.
IOM staff found the shallow graves of 29 people on a beach in Shabwa province during a routine patrol and provided medical care to 27 surviving migrants who had stayed on the beach, according to the United Nations -affiliated organization.
"The smugglers deliberately pushed the migrants into the waters since they feared that they would be arrested by the authorities once they reach the shore", an IOM emergency officer in Aden told AFP.
Survivors from the boat journey reported they were forced into the sea off the coast of Yemen after the trafficker in charge of their journey thought he spotted authorities.
Then they "simply went back to where they came from to pick more migrants and try to smuggle them into Yemen, again". IOM is working closely with the International Committee of the Red Cross to ensure appropriate care for the deceased migrants' remains. "This is shocking and inhumane", de Boeck said.
"They were all quite young, the average age was around 16", IOM spokeswoman Olivia Headon said.
IOM said around 55,000 migrants have left the Horn of Africa headed for Yemen since the start of the year, most aiming to find work in Gulf countries. It is estimated that a third of those who undertake this perilous route are women.
Some Somalis are desperate to avoid years of chaos at home with attacks by homegrown extremist group al-Shabab and deadly drought.
Despite conflict and a dire humanitarian situation, Yemen is still seen by many Africans as a gateway to the rich Gulf states or Europe, and thousands make their way there every year in crowded boats. IOM and its partners operate across the region to support these migrants and provide lifesaving assistance to those who find themselves abused or stranded along the route.