I'm glad to see that I'm not the only one stuggling on those ascalonian fishes !
I takes some times before dusk/dawn to "load" the fishing strength, get every possible buff, and get nothing...
The dusk/dawn fishes should have a better drop percentage than the other legendaries, as the dusk/dawn time window is already a difficulty : getting enough fishing power, trying to optimize the nodes to get as much as possible...
Still, I disagree on the mobs problems : it's part of the game to be attacked by mobs. You just have to jump off your boat, kill them, then jump back on your boat.
I really think i'll give up on ascalonian fishes success... It's really frustrating