Ibn Hazm (may Allaah have mercy on him) said in al-Muhalla (6/50): As for that which lives in the water and cannot live anywhere else, it is all halaal no matter what state it is in, whether it is caught alive and then dies, or it dies in the water and then floats or does not float, whether it was killed by a sea creature or a land animal. It is all halaal to eat, whether it is the pig of the sea (i.e., a dolphin), a mermaid, or a dog of the sea (i.e., shark) and so on. It is halaal to eat, whether it was killed by an idol-worshipper, a Muslim, a kitaabi (Jew or Christian) or it was not killed by anyone. The proof of that is the verses in which Allaah says (interpretation of the meaning): “And the two seas (kinds of water) are not alike: this is palatable, sweet and pleasant to drink, and that is salt and bitter. And from them both you eat fresh tender meat (fish)”
and “Lawful to you is (the pursuit of) water game and its use for food — for the benefit of yourselves and those who travel” . Allaah spoke in general terms and did not exclude anything, “and your Lord is never forgetful” . End quote.
Al-Durayr – a Maaliki scholar – said in al-Sharh al-Sagheer (2/182): Sea animals in general are permissible, whether it is dead meat or a ‘dog’ (shark) or a ‘pig’ (dolphin), and they do not need to be slaughtered properly. End quote.
Al-Saawi said in his commentary on that: The words “or a ‘dog’ or a ‘pig’ also include a ‘human’, referring thereby to mermaids. End quote. http://www.islam-qa.com/en/ref/103991/mermaids emphasis mineNeat stuff on that site. Did you know that the way to atone for accidentally killing someone is to either buy a Muslim slave and set them free or fast for two months? I didn't.