A couple M-80s or cherry bombs would really hurt their ears.
Hey, if a cherry bomb can wreck a toilet...
Some fishermen in the Monterey Bay region are using essentially a waterproof concussion explosive called a seal bomb to scare away seals and other small sea mammals from their fish catches. I believe that some sailors around Gibraltar are starting to carry M-80 and M-100 waterproof bombs that create a underwater concussive blast to scare away orcas.