Alarm Phone personnel spoke with one of the three survivors, who confirmed the nine passengers from Senegal died after the boat capsized in the Strait of Gibraltar, activist Maurice Stierl said.
The boat left the Moroccan port city of Tangier early Tuesday. Stierl said his network of activists informed Moroccan and Spanish authorities the migrants needed rescue shortly after the hotline received a first distress call that same morning.
A Moroccan team didn't reach the capsized boat until Wednesday, according to the survivor interviewed by Alarm Phone personnel. He said he was the first person pulled out of the water with a rope, while a woman who had tried to hold onto the same rope eventually drowned.
Spain's Maritime Rescue Service said it dispatched a helicopter to help search for missing passengers Wednesday, when a Moroccan crew retrieved the survivors and recovered one body.
A humanitarian group in Morocco, Walking Borders, reported four migrants missing Thursday from a different boat in the Strait of Gibraltar. Fisherman rescued eight people who had been on the boat that issued a call for help Wednesday, Walking Borders activist Helena Maleno tweeted.
Spain's government has increasingly ceded sea rescues to Morocco as part of efforts to reduce the number of migrants reaching Europe from the North African kingdom.
But activist groups such as Alarm Phone have argued Morocco's coast guard lacks the means and training to safely rescue migrants at sea.
The number of people arriving in Europe via the western Mediterranean route was down to 588 in March, the lowest monthly tally since 2017, according to the United Nations' migration agency.
More migrants appear to be making the trip as weather gets warmer. The International Organization for Migration reported 729 from April 1 to April 28.