I noticed that while catching Olgois, it's easier when u got gathering stat between 350-360. Never over 360. Also u can forget the perception food and buffs.
U need HQ Storm Rider for mooch, but the HQ rate for it is max 15% (I think, since it's 15% max for botanist and miner too) and u have already capped it since it's only around lvl 40 fish.
Rumors say that perception makes the fishes bigger, and harder to catch. So no need to buff ur perception, just in case. + u don't need the Olgoi-Khorkhois HQ
Also, for some fishes, too much gathering might be bad thing. I have Halcyon Rod Supra, and I don't use foodbuffs, unless the fish I'm hunting, requires high gathering rate. And for now, I have still been able to catch Olgois just fine.
So, just make sure ur gathering is around 350+

Ofc they might still escape, but u should be able to catch some =) Good luck!