I tame these on Scorched Earth in the blue ob cave. Just kite it into the water and come back later, it should have (for whatever reason) drained it's stamina swimming which also drains it's food completely (and does not have an affect on it's health) which will also make it's torpor rise. Just slaughter an ovis and throw the meat on AND GET IT OUT OF WATER ASAP BECAUSE WHEN TAMED IT DOES START TO DROWN... and if you're lucky you'll even just find these dudes at the bottom ready to tame randomly

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