Maybe it’s an exaggeration that a shark can smell a drop of blood from a mile away, I’ve read that they do have a remarkable sense of smell. But wouldn’t it take a long time for molecules of blood to spread so far in the sea to reach a shark that’s, say, a half a mile away? If I’m bleeding in the ocean a mile from shore, I assume that it would take a very long time for a shark to smell the blood unless it was already pretty close.
So what you are saying is that the sharks aren’t actually smelling blood that’s a mile away because they need the blood molecules to be in their nose. They are actually smelling blood that is in their nose? And it would take some time for the blood to travel that far?
Seems a fair assessment. I’ve more often heard the ability as being able to smell blood that is 1/ (some large number) water.
Yeah, it would take some time for the blood to spread through the water.
Mythbusters actually tested this. Sharks can smell one drop of blood in 25 gallons of water, and when they tested it, the sharks did react to that tiny amount of blood. But they didn’t react as soon as the blood was dropped into the pool. The sharks didn’t react until they actually swam through the area where the blood had been released. They did have a noticeable reaction to a very tiny amount of blood though, so that much is true.
Mythbusters also found what while the sharks did noticeably react to both a drop of fish blood and also to fish juice squeezed into the pool (literally, the guy just squeezed a dead bait fish over the pool), the sharks didn’t react much at all to human blood. I guess it just didn’t smell like food to them.
They tested lemon sharks, for what it’s worth. Most folks don’t have any great whites just swimming around in a tank that they can test with. Great whites typically don’t survive more than a few days in captivity. One aquarium managed to keep one alive for a few months, but the record prior to that was something like 16 days.
First, I have to recover from the 90’s style website that Grrr! linked to. Didn’t expect that.
I’d suggest that they update the “smell blood 0.25 mile away” to “smell blood when they swim through it” but I doubt that website updates very often.
Apparently some of the stuff I’m reading says sharks usually hear their prey thrashing about before they smell it.
I’ve always thought there was a popular science combination of a sharks keen sense of smell, and their more unique Ampullae of Lorenzini. Also a sharks hearing is particularly acute.
In my diving experience, sharks investigate primarily to electric stimulation I. E. A fish is distress, or certain audible queues, such as a fish swarming on coral, but when they swim directly thru the pool of blood, that’s what gets them frenzied.
So you prefer the modern websites that insist on running 5 million scripts, none of which actually improve the end-user’s experience on the site?
It’s only possible to smell things when the smell is right there under your nose. That’s how the sense of smell works - the molecules have to pass across your olfactory sensors in order to interact with them.
So ‘sharks smell blood at X distance’ here must really mean something like ‘sharks can smell blood that has travelled X distance from the organism that was bleeding, becoming typically diluted on the way’
Not really, it’s just that I was taken aback for a couple of seconds when that page loaded. I like seeing old websites like that, but I don’t see them very often.
It makes sense that a shark could smell blood and then use ampullae of Lorenzini to assist in locating the source. The ampullae look to be located on a shark to be sensitive to direction.
Sharks are said to be “living fossils” so the site is very appropriate. 
That’s what I figured. So when you smell a fart or dog poo, yadda yadda…
… your olfactory bulb is reacting to volatile gas molecules given off the fecal material or in the flatus - thiols, sulphides, indoles, skatoles etc at very low concentrations.
Yeah, not actually airborne solids, well, probably mostly not.