So, how I've been taming them without a skiff is figure out how many cannonballs it'll take less then or equall to 4 place down four cannons or 3 or how many itll take more then 4 place half the amount down (6 cannonballs/ 3 cannons, 5 cannonballs 3 cannons) load them up find your space whale gain aggro and run straight at the cannons (grappling hook helps for getting to cannons) the fire all as quickly as possible for 4 shots, for more then 4 fire them all (3 for 6 etc) reload and fire again as quicly as possible

Do not use rockets you lose over 50% taming effectiveness. Use a skiff and cannons

It only takes 9 kibble to tame a 140, please update

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

"Incomprehensible Whãle Noises"

Then Wåla! It is tamed!

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.

Its much easier to knock out with a Mek cannon all you need is one shot to K.O. if you can make a mek on your server its the easiest method by far.

Singleplayer taming is so hard. I had nobody to aim the cannon, and I'm currently waiting for the astercetus to wake up. I struggled so hard. He's a blue level 8. LEVEL 8. Dododex says there's a 93% chance of death for the cannon for a level 8.. Pretty lucky, eh? Singleplayer taming is.. Hard. Not impossible, though. I managed!

The best way is to use the Tek skiff which you unlock after the boss fight(like the saddle) and have cannons mounted on it. Probably easier with multiple people

Don't use mek because the astrocetus takes first the torpor and then the damage. The effectiveness will go down.
We tamed a 130 with mek and Kibble and get a 136 -.-
I think the stronger the weapon the more you loose the effectiveness, so the "best" way is to knock out with rocket launcher.
It's the same effect with rock elementals.
Wildcard should repair that.

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