At least 21 people were killed after a boat carrying migrants sank off the coast of Senegal, with only one survivor rescued so far, authorities said on Sunday.The Senegalese interior ministry said 21 bodies had been recovered by Saturday evening and search and rescue operations were continuing for possible survivors. The death toll was provisional, it added, without specifying how many people were aboard the boat.The boat capsized off Kebemer, about 180 km north of Dakar, near the Loumpoul dunes in northwestern Senegal, according to local media reports.Most of the victims were reportedly from the Leona and Thieppe districts in the Kebemer department, the Le Soleil newspaper reported.The latest tragedy adds to the toll of migrants attempting the perilous Atlantic crossing from West Africa to Spain’s Canary Islands. Thousands have died in recent years while attempting the journey. At least 635 people died along the route in the first five months of this year, according to migrant rights group Walking Borders.The incident came a day after Senegalese authorities intercepted 142 migrants aboard another small boat allegedly attempting to reach Spain. The group included 23 women, two babies and two other children, and comprised nationals of Senegal, Gambia, Guinea-Bissau, Guinea and Nigeria.The Senegalese government said it was determined to combat people-smuggling networks, including through stronger cooperation with neighbouring countries.Meanwhile, authorities on Spain’s Canary Island of El Hierro declared an emergency on Saturday following a surge in migrant arrivals. More than 3,300 people had reached the island aboard around 30 boats since the beginning of November, according to local authorities.Senegal, Mauritania and Morocco have stepped up maritime patrols near departure points, pushing migrant boats further south towards the coasts of Gambia, Guinea-Bissau and Guinea, lengthening an already hazardous crossing.