I don't know if there'd be any way someone on a boat could deal with something obviously carving away their boat. If anything they might abandon it for the life boats. But then that just puts them closer to the water and easier to grab by anything with the arms to scrap at the bottom hull of a boat.

So it then comes to a matter of if the means justify the effort. We might as well look at the fish people as being someone so ecologically divided they're pretty much completely isolated from surface affairs. There's not much they can both to do that'd be worth the effort.

Of course, this whole lampshading discussion could be avoided if the fish-people in question were more amphibious than not...

[img]http://www.mobygames.com/images/shots/l/267356-the-witcher-windows-screenshot-vodyanoi-the-denizen-of-the.jpg[/img]