Hi Bob, looking forward to seeing the photos of the huge snapper that you caught. As to marking snappers for your research project I'm not sure what to do without harming the snappers. I thought of rubberbands at the base of the tail or in between the tail keels. I would be worried about the bands cutting off circulation though especially on growing snappers. Or a permanent black marker on one of the claws might work temporarily. What kind of a reasearch project are you thinking of doing? Hope this helps.