I've had one leave the plastic end cap down the hull tube, but not a piece of the aluminum tubing. That's nasty looking.
You need to get it loose first - and from the looks of it, it's pretty well corroded / welded to the fiberglass tube.
Fortunately, the fiberglass is impervious to almost all solvents, so you might as well try soaking it in a penetrating lube like Kroil (
http://www.kanolabs.com/). Soak it for a day, give it a few light taps with a long screwdriver and see if it moves. Repeat. It could take a while.
Theoretically, an acid solution will dissolve the aluminum (eventually, depending on how strong the acid is), but using severely corrosive / caustic liquids isn't to be taken lightly. You don't want to do this if the tube leaks at all - you'll have acid inside the boat.
Once it's loose, you should be able to fish it out with a bent coat hanger.