Presas is a word in feminine plural form and could mean one of three things in Portuguese: prey, arrested/tied/stuck (as in 'two women were arrested' - "duas mulheres foram presas" or 'we're stuck' - "estamos presas"), or claws/sharp teeth/fangs.
I've never seen it used as a surname, but if I had to guess which of the three meanings is the one you want, I'd say it's the last one, since it seems to make more sense than the other two.