According to this page,
You must be registered for see images
Whitebeard's words: shanks already was yonkou tier back then. It's almost confirmed that he could use Armament Haki, so why did'nt he just use armament haki on his arm for a beast like that? He just, apparently, used conquerors haki instead of armament haki, that just does not make any sense. It wasn't a strong sea-monster, luffy pre-timeskip defeated him with his weakest punch
Is this the first Oda's plot-error or Am I not seeing something like he was too busy using his haki to allow him to move in the water?
I found this question on a site and I quite agree with some of the answers there. And from some multiple answers I framed my answer.
But I am just excited to get some responses from the base.