What is likely happening is that the sharks can smell the blood but it’s just not in a quantity that is interesting to them especially since they don’t love human blood that much (btw, I spoke with a marine biologist and mammal blood is all the same from a chemical marker stand point so cow blood is a suitable substitute for human blood). If I did the experiment again, I would want to test human blood vs. fish blood.

This is the most definitive study done to date in a control lab environment on what is least and most interesting to them: The Biology of Sharks and Rays Peter A. Klimley and Steven Oerding; ISBN-13: 9780226442495. Particularly pages 134-140. Figure 6.7; Table 6.2

t’d be super interesting to repeat this experiment off the beach (anchoring boards so they don’t drift back inland) without the presence of a distracting boat, where people are most concerned about shark attacks and less likely to be as shark informed as the ocean divers. Though I imagine at places like the Bahamas the scenario Mark tested on would be more common.I think the reason sharks disnt catch so much to the blood experiments was that prey move when hurt and bleed, just having stationary boards is like.. well the sharks are smart also Mindblowing video as usual! Maybe the sharks had already learned from the previous experiment that there was nothing of interest at the surfboards despite the blood and that’s why they didn’t investigate again…