Some fish, like sharks, don't posses an air bladder to help keep them afloat and must either swim continually or rest on the bottom.  

Bull•Shot/Drop Shot Rig

May 23, 2011 | Categories: Fishing Tips

This rig not only brings up winners, it’s also a great value because Bull●Shot works better than regular drop shot at a fraction of the cost. When working your bait off rocky bottoms, tie a palomar knot with a 2-3 foot tail and a Bull●Shot attached to the end. If your rig gets caught in the rocks, tug on the line until the Bull●Shot slides off and your bait is set free. Adding another Bull●Shot is a lot better than replacing your entire rig.