k ive caught snappers... 20 lbs is pretty fuckin big but...
lure it with something.. fish heads hotdogs anything.. if you can get it up to something shallow that is better. the key is you gotta pick that bad boy up by the tail.. either that or make a pole and rope snare...
at6 any rate there are some ideas but pick it up buy the tail and put it in a bucket or a live trap like they do with lobster and fish