I’ve repeatedly seen documentaries that marvel at sharks and their ability to smell a miniscule amount of water in the ocean from miles away.
From what I’ve seen, this is legit. But how the hell does it work? How does a small quantity of blood, diluted by trillions of gallons of water all around, maintain enough particles that they can be detected through smell at a great distance? And how do the particles travel that far in a short amount of time? Are currents required or just one method? It seems that the smell travels faster than you’d think possible via currents, but is this just poor explanation on documentaries and compressed time (as an editor, I’m aware of that being probable, but usually there’s some idea given as to how much time has passed).
Many animals have well developed senses beyond what humans are used to. Our humble dog has an olfactory membrane of ~150cm[sup]2[/sup] compared to human’s 4cm[sup]2[/sup]. To a dog humans would be considered severely handicapped when it comes to smell.
Sharks, like dogs, simply have a highly developed sense of smell and are programmed to tune in to the scent of blood. Depending where you look for cites (I checked a few) and probably depending on the shark in question they can sense blood anywhere from 1 part per million to 1 part per 10 billion (i.e. 1 blood molecule in 1 million molecules of water). 1 part per million equates to ~1 drop of blood in 25 gallons of water.
Humans make sensors for all sorts of things that are far more sensitive. As amazing as a shark’s sense of smell is it is nothing more than a well adapted/evolved sense.
To smell the blood the blood molecule must travel from the wounded animal to the shark via ocean currents. However, the sharks has a “lateral line” used to detect motion in the water that allow it to tune into animals in distress in the water (thrashing human, spazmodic fish in its death throes, etc.). In some fish the lateral line is so sensitive it can detect ripples in the surface of water to cath water skimming insects. This sensor along with the shark’s electoreception ability is likely what draws it to an area where a wounded animal is much faster than the smell would reach it so it seems the shark appears faster than one would think possible.
I saw in a documentary that humans need about 2 billions scent molecues present to be able to smell something, while bloodhouds need about 5. Molecules, not billions. I figured sharks were similar, but the speed of their response is what confused me. Thanks for the clarification!
PS - Been a while since I saw the documentary, so my molecule figures can easily be wrong. =) But it was a range of somewhere in that magnitude. So the point is valid! Heheheh
Should menstruating girls and women avoid the ocean? You’d think they’d teach this at every school in Florida (& California, & South Carolina, & son on) if this were true.