Well, for starters, you don't need HQ olgoi for Supra

And secondly, I found that when I was on the lower end of the gathering requirement, I caught far more Olgois, then when I maxed my gathering.

At 350~ gathering, I caught 9-10 olgois with maybe 3 "fish gets away".
At 390~ gathering, I have only had "fish gets away" on about the same number of attempts.