That's for northern hemisphere islands I'm pretty sure. Most sites default to the northern hemisphere dates since that's where most people play. I could be wrong though!
I'm in the northern hemisphere. They're everywhere. If you haven't caught one yet, then we can conclude that March is not accurate for your location and that yukimin is right about this one.
Don't trust those websites too much. The game is out for less than a week and they know hardly anything at all, but they provide (often false, inaccurate or incomplete) information anyway because they know people will be looking.