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.

DONT AND I REPEAT DONT USE THE ROCKET LAUCHER ON THE SKIFF IT WILL DESTROY THE SKIFF AND KILL YOU

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

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.

Taming with a mek makes it loose roughly 40% efficiency, if you have got a skiff its better to use that

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

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

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!