Contact TPWD with the TX numbers and let them know. I'm sure the owners will be driving around and attempt to recover them before long. I found a johnboat in my front yard in Terramar, I'm sure it came from across the canal. I'm not too worried about thieves stealing boats, I'd guess their more interested in things to sell easily, like electronics.
I called TXPW and asked for the owner info on a set of TX numbers. They told me I had to fill out a form in person and would not tell me any info over the phone. Nice way to help out these lost boat owners don't you think ? Very dissapointed.