He might not know a lot about Mermaids and humans, but he does know they shouldn't mix. Which is why being forced into a tank with a mer on some random human cruise ship is... concerning, to say the least.
Contrary to popular belief, sirens are nothing like mermaids. Sure, they're both sea creatures with the upper body of a human and the lower body of a sea creature, but that's where the similarities end. Sirens have beautiful singing voices and are a dominantly female species (Dick is a rare exception) found in rough, cold waters where only the riskiest of humans will dare to go. Mermaids are equally balanced in gender and can be found living their best lives in tropical waters near coral reefs or human populations. Sirens are killers and mermaids are human-loving ninnies.
Dick spends his days lounging below the surface, waiting for human ships to sail by. Usually, he goes for boats with single occupants or small crews. It's not smart to go after a big ship with hundreds of people. He skips over cruise lines and cargo ships. He doesn't see many of the large ships due to being in such a rough part of water, but when he sees one he makes sure to go deeper than he prefers. He'd rather be uncomfortable for a few minutes than risk getting harpooned or captured.
Sadly, he's not always fast enough to avoid being seen. He can count on his webbed hand how many times he's been spotted by someone who lived to tell the tale, which is 3 times if you were wondering. When he's seen it's by some eagle-eyed nobody who can't do any real damage or are smart enough to turn tail and run.
With that knowledge, it's a shock to hear that he was not only spotted, by captured as well. He's known a few ships to come by, searching for rare creatures, so a siren, and a male at that, is like a jackpot. He tried to run, but something struck him and he fell unconscious. He doesn't remember much between being dragged out of the water and sloshed around like he was a dead fish.
He woke up in a strange place with the strong smell of chlorine. That probably explains why he feels so poor. He looks around and frowns when the only thing around him is pale walls and.... the reek of humans. He swims to the top of what seems to be a container. He flops out and alarms sound. He thrashes and tries to hide before anyone can flood the room, but it seems the humans who've captured him have other plans. He flops onto a false floor and falls through it. He gasps and flips midair to land on his stomach, belly-flopping into a new container. His head hits a decorative rock and he goes limp, unconscious.
He wakes up again for the second time that day to the god-awful ~~beautiful~~ face of a mer. He groans and tries to sit up, only to be kept down by a hand. He stares at them. "Get your dirty grippers off of me. Don't you know what I am? I could eat you alive and you wouldn't stand a chance." Oh, he can feel something in his mind going off. That's probably the chlorine he can still feel in his gills.
"Where am I? Why am I in a tank with a dirty human lover? What is this- are those humans staring at us?!" He backs away and thumps against the glass furthest from the new human faces that were staring in awe. Don't they know he's a killer?