In interviews, survivors provided harrowing accounts of their ordeal: an attack helicopter that passed overhead six times, spraying them with bullets; fishermen jumping from flaming boats into flaming waters; survivors drifting in the water for days on end, watching helplessly as friends and brothers slipped under the waves.

Of the 86 fishermen on the six boats, 50 died.

Identifying the perpetrators of maritime attacks is notoriously difficult, especially in a war as chaotic and opaque as the one in Yemen. Both the Saudi-led coalition and its Houthi foes, who are backed by Iran, have carried out attacks at sea.

But maritime experts, a former United States Navy officer, United Nations investigators and several Yemeni officials said there was little doubt that the Saudi-led coalition was responsible for some if not all of the violence against fishermen.

Saudi and Emirati naval boats dominate the Red Sea waters where the shootings and bombings took place. Five involved attack helicopters, which the Houthis do not have. In one instance, Saudi officials made cash payments of nearly $500,000 to the families of fishermen killed in an attack.

In another, coalition sailors detained 12 survivors and held them for three months in a Saudi prison, where the fishermen said they were interrogated and tortured. Eight of those detainees were recently released after receiving a payment of $1,300 each from their Saudi captors.

“A soldier posed with us in the prison for a photo and said, ‘Sorry if we hurt you,’” Yaqoub Okad, 20, said in an interview after his return to Yemen.