[Anthony]

It would certainly be possible to have sophisticated underwater grappling techniques, but they simply won't look all that much like the ones you use on the surface because of the whole way footing and leverage work underwater; it's probably a straight-up different skill. Various types of joint locks are probably the most transferable, though a lot of those moves would be specific to the morphology of the target and thus anti-sahaugin moves and anti-human moves might not be the same.