Bus route from Port Louis to Mer Rouge ( Rivulet Terre Rouge Bird Sanctuary)

It's walking distance, 9 mins on foot. Check Google Maps:

I haven't travelled by bus for a long time now so your best bet is to ask the bus drivers/conductors at La Gare Le Nord if you really want to know which bus goes there. On a side note, it might cost you roughly the same to go by taxi marron (taxi train) as to travel by bus.

Hope that helps :)