He was wandering through the deep sea in search for food coming up to the surface spotting a group of fish close to the top though noticing it wasn’t a group of fish & it was a net as he got tangled in it before he could realise and rushed upwards to where he thought he spotted food

Your crew pulled the net throwing the shark merman on the dry wooden deck as he flailed his tail fin around trying to get out of the net failing, clearly mad, spooked and slightly scared