The bodies of 13 would-be migrants have been found on board a makeshift boat off Spain's Canary Islands, an official said on Thursday. Thirty people survived, but three of them were in serious condition and were sent to hospital, a government spokesman in the Canary Islands said. He said the migrants may have died of hypothermia because the weather was cold and rainy. The boat was spotted by Spanish police off the island of Fuerteventura and towed to port, according to news reports. Officials could not say where the migrants were from. Thousands of Africans attempt the treacherous journey to the Canaries or mainland Spain each year in search of a better life in Europe, usually making the crossing on long, low-lying boats operated by smugglers. Moroccan immigrant group ATIME estimates some 4,000 people have died since 1997 in the attempt. Two would-be migrants died while attempting to reach Spain but another 35 were rescued on Wednesday when their flimsy boat ran into trouble off the Canary Islands.