I've fished up the turtle mount twice on two different characters. Both we're in Northrend, in WOTLK days. My first was a Druid who maxed her fishing and eventually got it. The second was my DK who went from 1 to about 200 something and got it.
Now, I'm on my Goblin hunter, been fishing in Northrend for a week- stopped leveling, fishing nonstop, I want this mount before Vashj'ir. What I'm trying to ascertain now is whether or not you can still catch the mount in Northrend? Are we sure it's not JUST Cata pools, can we confirm it is still Northrend and Cata content?
And for what it's worth, I did manage to fish up the Dustbringer. :/