Seven bodies were found on the boat and an estimated 56 people were missing at sea and presumed dead, said International Organisation for Migration spokesperson Safa Msehli on Thursday.
The Spanish migration advocacy group Walking Borders said the vessel was a large fishing boat, called a pirogue, which had left Senegal on July 10.
Families in Fass Boye, a seaside town 145 kilometres north of the capital, Dakar, reached out to Walking Borders on July 20 after 10 days without hearing from loved ones on the boat, group founder Helena Maleno Garzón said.
Cheikh Awa Boye, president of the local fishing association, said survivors called home from Cape Verde after the rescue. Boye said two of his nephews were among those missing.
Spain's Maritime Rescue Service confirmed that a Spanish fishing boat named the Zillarri rescued 38 people and recovered seven bodies from a Senegalese pirogue on August 14 after spotting it adrift north-east of Cape Verde.
An official of the tropical tuna fishing company PEVASA, which operates the Zillarri, said the survivors were asking for help and were in a "bad state".
The route from West Africa to Spain is one of the world's most dangerous, yet the number of migrants leaving from Senegal on rickety wooden boats has surged over the past year.
The boats try to reach Spain's Canary Islands, an archipelago off the northwest coast of Africa that has been used as a steppingstone to continental Europe.
Nearly 1,000 migrants died while trying to reach Spain by sea in the first six months of 2023, Walking Borders said.
Worsening youth unemployment, political unrest, violence by armed groups and climate change push migrants across West Africa to risk their lives on overcrowded boats.
Nearly 10,000 people have reached the Canary Islands by sea from the north-west coast of Africa so far this year, according to Spanish Interior Ministry figures.
On August 7, the Moroccan navy recovered the bodies of five Senegalese migrants and rescued 189 others after their boat capsized off the coast of Western Sahara.
In 2021, an AP investigation found at least seven migrant boats from north-west Africa had become lost in the Atlantic and were found drifting across the Caribbean and even off Brazil, carrying only lifeless bodies.
Sign up here to receive our daily newsletters and breaking news alerts, sent straight to your inbox.
