What I have seen with hammers is that a lot of people grab them behind the T-Bone and they grip hard as the hammer's writhe around a lot. These hammers dive straight to the bottom or beach themselves. What the guys don't realise is that grabbing and holding tightly behind the hammer you are crushing the gills causing the fish to suffocate.
Interesting reading this, saw a doccie on Hammers, they reckon the actual design of the hammers head works like the wings of an aircraft. The "t-bone" itself is hollow with no organs, and a slight tilt up or down of the "wings" make it the most agile shark in the ocean. Also, because the eyes are on the side of the head, it needs to move it head from side to side in order to see the "full picture" in front of him. Is it possible that when we handle these sharks by the "t-bone" as you said, that we in fact bugger up the alignment of these bones, thus the fish dive straight to the bottom?