My band always sang, in verse 2 "Some old portly porpoise sporting in the foam" (better alliteration) and in verse 3 "Sharks all sang in chorus, splashing in the brine" (marginally better cadence)--and both of these are how I remember Regal Slip singing it, though that was a long time ago...

Oh, and I think it's "lockjawed" -- a better rhyme with "board."

We also sang "Six sharp shivering sharks are sure to snap your limb" even though that's not how Regal Slip sang it, because we thought "sure to" sounded better than "gonna" (also it's another sh sound, so it increased the tongue twister factor).