Im sure at one point or another you have been swimming and had this incredible yet vile feeling come over you, a feeling that you were being watched and scoped out from beneath. For you at the time, this was probably just a feeling, but it could be a reality. So how do sharks smell blood from great distances? Here is the science and anatomy as we know it.
As sharks swim through the water, they are constantly taking samples. When they are swimming, water passes through their nostrils and into a tube shaped organ, where it is then led into their nasal sacs which is lined with millions of receptor cells. As you may have heard before, a sharks sense of smell is incredibly sensitive- so sensitive, in fact, that the sharks receptor cells can pick up an average of one part blood in 25 million parts water. Incredible! Given the right scenario, a sharks sense of smell can be even greater.
One particular Test done with Black Tip Reef sharks showed how incredible the sharks nose really is. After these test sharks had not eaten in a while and were really hungry, they went to drastic measures. Because of the particular circumstances, these sharks could detect one part blood in 10 billion parts water. Quite a scary thought if you are in the ocean while you are bleeding.
Not to worry, sharks do make use of their other senses, but not nearly as much as their sense of smell. They use sight and hearing to home in on their victims, but other then that, its up to their nose.
The Quirks and Quarks Question Book