Steel shot shotgun shells
Shotgun shells won’t penetrate. Probably the best thing would be to have a Coast Guard cutter come by and lace the carcass with 50-cal steel-jacketed rounds out of an M-2, or maybe a LAV with a Bushmaster and some DU rounds. A couple hundred 50cal rounds or a few dozen 25mm DU rounds at sub-200-yard range ought to go deep enough to ventilate the various organs, and provide enough outlets to decompress all the gas pockets. After that, it’ll be the messy job of slicing the thing up.