I just want to confirm that I caught another shark on March 13th in Borean Tundra open water on my level 10 druid with maxed fishing and effective 555 skill (strong fishing pole and +100 lure). I fish where I can catch dragonfin angelfish. Got it a half hour in, and had only caught 8 pygmy sucker fish up to that point. My previous several catches were bonescale snapper.
It's just luck, folks. That's 3 sharks so far out of about 6 derbys, all fished open water. I think maybe being able to catch fish non-stop instead of hunt for pools and cast and recast until you land in the pool actually makes up for the higher drop rate in pools.
Got a lure, some gold, deviate fish, and a piece of glass junk in my bag. I was going to save it and see if the contents changed with the patch, but I tried to link it in chat and accidentally auto looted it like a stupid noob. Oh well, I guess I'll just have to catch another.