I had discovered this recently, too and almost posted about it.
I was getting tired of missing fish and/or not being able to fish in Outlands. My skill was around 320, plus +20 pole, +2 gloves, and lure, but still was having trouble. So, I decided it was time to head back to the old world to fish for a while and get my skill up. Well, Feralas is kind of a favorite of mine because of the fish types and the nice run of pools along the coast. I was guild chatting and fishing simultaneously, so I was just standing next to the dock at Feathermoon rather than running the coast. And obviously I notice I'm pulling two fish out at once. My thought at the time was it was that it was skill related but, sounds like it's zone related. It's definitely a good way to catch a lot of fish in a hurry. Eels, firefins, blackmouths, winter squid, summer bass, clams with the occasional pearl. Good times.