The boat carrying 300 people had left The Gambia and capsized near Nouakchott, according to UN migration agency.
Dozens missing after fishing vessel left from border of Senegal and Gambia with 170 believed to have been on board.
Ghazouani secured 56.12 percent of the vote, well ahead of his rival Biram Dah Abeid, says the electoral commission.
President Mohamed Ould Ghazouani won 55.7% with more than 91% of votes counted, electoral commision data shows.