Use a bloodstalker and a rocket launcher, jump around to its face and shoot it with rockets until it knocks out. Jump off the stalker and land on the whale to quickly feed it.

Mek cannon one shot KOs any level. Also they seem to tame about 3x faster than what dododex says here... Needs more testing though

To tame these, you have to learn Whãle from, Dory.
Ahem.
"Ooo Ooo" "OoWaoooo" "Huff. Huff."

"Incomprehensible Whãle Noises"

Then Wåla! It is tamed!

You can actually knock it out with a Mek Cannon if you do not have the Tek skiff.

Obtain a Tek replicator from tier 3 crates in the shop, and craft the Mek from the engram

I used a ufo with a canon didn't take long to knock out and was able to do solo