Since I've been fishing, I realized that only a few places (Summerset) are really good for repeated fishing. The rest once you get the achievement, you needn't ever return. If there were a crafting motif for each type of fishing hole (Foul, Lake, River, Saltwater, and perhaps Oily in Clockwork City), you could interest people in repeated fishing. Perhaps a low % of motif drop that comes in the gunny sacks?

The other idea: replace some seashore sweepers with landing boats / parties of Maomer invaders. So instead of the sudden appearance of Dremora and the like, you'd instead be walking along and a boat would row up to shore and a couple of waves of Maomer would unload, and then a boss. The boss would potentially drop a crafting motif page for a Maomer style, or perhaps a pirate style in waters where the Maomer don't commonly sail.