The Lost Island, I can't remember the movie?

I think It's title is "The Lost Island" but when I search it none of them is what I'm looking for. I'm searching for the movie... the story was... There are a group on the boat and suddenly a mermaid (I think it's a mermaid or octopus man) attacked the boat then the boat has a hole. So, they need to move on.. Then they went to an island that is not recognized, I remember the protagonist one male and one female... They went to look for a hotel and they noticed the neck of the guy who's managing the hotel has fins on his neck.. and then when the protagonist went to his room, he saw a black blood on the bed then he looked at the window he saw a group of people looking for human to eat. So, they saw him looking on the window and then run to go to his room but he jumped on the window. So, when he figured out that people there are man eater, he sneaked and he looked for the girl. When he entered a room, he found a girl lying on bed with a blanket on her feet.. suddenly someone knocked and the protagonist did a sign to the girl that she must not tell where he is. So the girl lied, and when they got away, the protagonist fell for the girl and kissed her, but when she took off the blanket he saw a tentacle, so she's half octopus? That's all, I think the people there on the island did a ritual and did a sacrifice at the church and that happened to them... and they eat people. They look like human but has fins on the neck. At the ending, the girl was about to use as a sacrifice but the guy protected her and burned his belly but he jumped to the water and he saw his belly that he's one of them.. his belly has fins.. and neck.. he realized...End. This is old movie I think. ._. Please help.