"Carnival" (Spanish "Carnaval") is held on Shrove Tuesday, known to the Spanish as Mardi Gras (literally Fat Tuesday), which is the Tuesday immediately before Ash Wednesday, 40 days before Easter Sunday. It represents the last available day of feasting before the abstinence of Lent (whose first day is Ash Wednesday). "Carne" means meat, so it is a day for gorging on meat, before then giving it up for 40 days. All stems from Christian (mainly Catholic) dogma, though Shrove Tuesday (to Anglicans) aka Mardi Gras (to Catholics) are most certainly not religious festivals themselves. The next day, Ash Wednesday, is. I don't know what the Spanish call Ash Wednesday, but they most certainly "celebrate" it as it is one of the fundamental days in Christianity. Here (San Pedro) it seems of remarkably little significance.