[neilep (OP)]

Dear Sharksters,

This is a happy shark:

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Notice how happy he is ?..he's having a jolly happy time because he'd detected a load of this:

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Now apparently Hubert(That's his name) can detect the red stuff up to a whole mile away !

How does he do that ?...I assume he MUST be down current of it yes ?..if not then how ?...and how long does it take for the detection of the blood from it's original location ?..a generalist guestimate will be nice

[dkv]

Living in the water is no easy.
Half a mile is not a big distance to search for the food when there are miles and miles to cover.

[neilep (OP)]

Thanks DKV,

I am trying to understand how, after so much dilution, does the shark pick up the taste/smell.  Clearly he must be down current from it yes ?...if he's not down current then I am really confused as to how he detects the blood !

[Karen W.]

Here is where I found this!

http://www.amnh.org/learn/pd/sharks_rays/gallery_week4/

   

blood in the water!
A drop of blood...


Myth:

Sharks Can Detect a Single Drop of Blood in the Ocean!

Sharks are often portrayed as having an almost supernatural sense of smell. However, reports that sharks can smell a single drop of blood in a vast ocean are greatly exaggerated. While some sharks can detect blood at one part per million, that hardly qualifies as the entire ocean. Sharks do, however, have an acute sense of smell and a sensitive olfactory system--much more so than humans. Sharks' nostrils are located on the underside of the snout, and unlike human nostrils, are used solely for smelling and not for breathing. They are lined with specialized cells that comprise the olfactory epithelium. Water flows into the nostrils and dissolved chemicals come into contact with tissue, exciting receptors in the cells. These signals are then transmitted to the brain and are interpreted as smells.

Because of the extreme sensitivity of these cells, as well as the fact that the olfactory bulb of the brain is enlarged, sharks can detect miniscule amounts of certain chemicals. This varies, of course, among different species of sharks and the chemical in question. The lemon shark can detect tuna oil at one part per 25 million--that's equivalent to about 10 drops in an average-sized home swimming pool. Other types of sharks can detect their prey at one part per 10 billion; that's one drop in an Olympic-sized swimming pool! Some sharks can detect these low concentrations of chemicals at prodigious distances--up to several hundred meters (the length of several football fields)—depending on a number of factors, particularly the speed and direction of the water current.

Predation is not the only behavior in which olfaction plays a crucial role. Evidence exists that this keen sense of smell is also instrumental in sexual behavior. Males are able to detect pheromones produced by females, even in low concentrations, helping them locate potential mates.

See also:

The Sensory World of Fishes
http://www.csuchico.edu/~pmaslin/ichthy/Snsry.html#start
This site presents the basics of shark's senses, including smell.

Topics in Shark Biology: The Nose Knows
http://www.reefquest.com/topics/nose.htm
This site provides a thorough discussion of shark olfaction.
   back
   

[dkv]

How long the "smell" travels is debatable... it must be an easy task for sharks. They live in a vast space. The degree is freedom in very high.
Sharks motion is horizontal vertical both.
Therefore saying that current is required to determine position is short sighted.
The answer lies in extraordinary ability to distinguish between waters..Waters at home and water far away.
How much of change produces a signal will be interesting subject of research.
Consider some medicines like Homoeopathic ones.They dilute a drop of poison in Ocean to make it a medicine...(some claim it is placebo effect but the issue is debatable as horses and animals also get benefitted.)