I've only done ~4 locations but it seems you can get through 2/3 of the fishing log and then you get left with 1 or 2 stubborn blanks. Like in Limsa Lower, I had two blanks until I caught an anchovy then mooched it to catch a Blue Octopus. The other one I think must be from using mooch with the ocean cloud (at work, forget its exact name).
They need to add a tacklebox; FSH just blows up your inventory between all the bait and random fish + HQ fish taking up another spot.
At work, but I plan on spending a lot of time tonight fishing.