This is Jack's first time seeing mermaids up close. He vaguely remembers spotting one on distant rocks as a child, but everyone accused the boy of making it up. So much so, that he began to believe that was the case. He's heard stories of them being both benevolent and wicked and has never been certain of which to believe. Now he knows.
He's running out of air and his pulse is pounding in his skull as the wrestle with him. He would rather not be a meal for either of them, really. The very second he's free, he tries to swim for the surface, only to be batted back down by the stronger male. He tries again and is batted down again. When the thing becomes bored with him, Jack is very dizzy and feels consciousness slipping. He summons the last of his strength to claw his way up through the water. The surface seems miles away until his head finally breeches into open air and he starts gulping in huge breaths.
Jack struggles to pull himself back into the boat and flops onto his back to rest for a moment, panting desperately for air.