(We're allowed to find this disturbing, right? Because even though I know I must be missing something somewhere...this scares the living spit outta me!)
It was squarely intended as black humor. Seeing beautiful mermaids being clubbed to death couldn't be anything less. Of course, the idea was that the mermaid killers have perfectly legitimate reasons for what they do, and that our society somehow needed something from the slaughter.
On the one hand I have to say that once again you've managed to make wonder about your thought processes, on the other hand a film like this, if properly done, could turn a handy profit so if you need investors call me.
That's always the trick. Done right, a weird idea is a cult masterpiece. Done wrong, it's just tripe - or even worse, annoying tripe.
I will be your DP, Andrew ~ but the running time is a little short.

Are there any nice, white sand beaches in your neck of the woods?
Recommendtaion: Theatrical running time: 102 minutes. Director's cut DVD: 206 minutes.
Ha! Your suggestion is more practical than the idea merits.