NOUAKCHOTT, March 6 (Reuters) - More than 40 African migrants heading for Spain's Canary Islands drowned at the weekend when their boats sank off the West African coast, Mauritania's Red Crescent organisation said on Monday. More than 40 other migrants were rescued in the incidents, which took place in waters north of the Mauritanian coastal city of Nouadhibou, off the coasts of Western Sahara and Morocco, a Red Crescent spokesman said. "There were two shipwrecks from Saturday to Sunday," Ahmedou Ould Haye told Reuters, speaking by telephone from Nouadhibou, Mauritania's second city and biggest port. Most of the Africans involved...