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.... to be entirely cursory & not compelling as written.
This is not to say that she is incorrect, only that she does not prove the case & that a more scholarly treatment appears warranted.
The scientific truth is that the smell & taste receptors of many carnivorous sharks routinely permit the recognition of one part of blood in 100 million parts of water. With some species under some conditions, e.g., food deprivation, this sensitivity can be very much higher. Those expert in the central nervous system of the shark have suggested that two-thirds or more of its brain may be devoted to smell. I, for one, believe that there is a sound evolutionary reason for this.
Unfortunately, no studies of which I am aware have specifically tested for menstrual blood. However, the extensive research findings on fresh human, animal & fish blood, other human bodily fluids, e.g., urine, and a wide variety of water-borne organic chemicals found in human fluids (e.g., amino acids, amines & small fatty acids) indicate to me that the carnivorous shark's exquisite sensory capabilities can in fact detect menstrual blood, and at a considerable distance.
Although the blood lost during menstruation typically is small & occurs over several days, there simply is no argument but that, most especially on the days of heaviest discharge, it is more than enough to be detected by a creature that not only can sense one part of blood in 100 million parts of water or better, but also often can tell which of its nostrils that part is closest to.
So much for detection, as "ratherbediving" is inquiring about any increased risk of shark attack during menses. Again, to the best of my knowledge there is no research on this, and for obvious reasons controlled studies would be difficult.
Dr. McComb's short paragraph on the subject includes the sentence, "The hemolytic blood associated with menses may instead act as a shark deterrent (Edmonds, et al., 1992, p. 65). " One will want to be aware that Dr. Edmonds arrived at this conjecture based solely on the statistical finding that women are attacked by sharks less often than men. Clearly there a many possible reasons for this statistic having nothing to do with menstruation.
There as well are several credible sources who opine that risk may be increased. These include George Burgess, Director of the International Shark Attack File, and Divers Alert Network (DAN). An article on shark attack in the Feb '02 issue of their "Alert Diver" magazine states: "Although there is no positive evidence that menstruation will increase risk, it is best not to tempt a predator that finds its prey via smell" (p.15). As with Dr. Edmonds' comment, this other position also is without direct research support.
In addition, in the thread cited above by "Walter," http://www.scubaboard.com/showthread.php?s=&threadid=340, you will find several anecdotal reports of menstruating divers being hassled by sharks, and I can provide others if you like. And while we are here, I'd like to expand upon a reference made by Walter within that thread concerning the work of H. David Baldridge & his colleagues back in the 1970s. To the best of my recall, this work in essence demonstrated that sharks prefer fish to mammalian blood, not that mammalian blood isn't of interest to them.
My personal opinion is that there may be a very small increased risk of shark attack related to menses. But, as the risk of shark attack on a diver is already so infinitesimally small, and even smaller on women, it would be extraordinarily difficult to prove the matter one way or the other even if controlled studies were easily done.
This having been said, if I were a woman & was otherwise feeling up to scuba I would not alter my dive plans due to menstruation.
Of course for you hardy ladies diving cold water in drysuits, the whole discussion lacks relevance.
Best regards.
DocVikingo
This is not to say that she is incorrect, only that she does not prove the case & that a more scholarly treatment appears warranted.
The scientific truth is that the smell & taste receptors of many carnivorous sharks routinely permit the recognition of one part of blood in 100 million parts of water. With some species under some conditions, e.g., food deprivation, this sensitivity can be very much higher. Those expert in the central nervous system of the shark have suggested that two-thirds or more of its brain may be devoted to smell. I, for one, believe that there is a sound evolutionary reason for this.
Unfortunately, no studies of which I am aware have specifically tested for menstrual blood. However, the extensive research findings on fresh human, animal & fish blood, other human bodily fluids, e.g., urine, and a wide variety of water-borne organic chemicals found in human fluids (e.g., amino acids, amines & small fatty acids) indicate to me that the carnivorous shark's exquisite sensory capabilities can in fact detect menstrual blood, and at a considerable distance.
Although the blood lost during menstruation typically is small & occurs over several days, there simply is no argument but that, most especially on the days of heaviest discharge, it is more than enough to be detected by a creature that not only can sense one part of blood in 100 million parts of water or better, but also often can tell which of its nostrils that part is closest to.
So much for detection, as "ratherbediving" is inquiring about any increased risk of shark attack during menses. Again, to the best of my knowledge there is no research on this, and for obvious reasons controlled studies would be difficult.
Dr. McComb's short paragraph on the subject includes the sentence, "The hemolytic blood associated with menses may instead act as a shark deterrent (Edmonds, et al., 1992, p. 65). " One will want to be aware that Dr. Edmonds arrived at this conjecture based solely on the statistical finding that women are attacked by sharks less often than men. Clearly there a many possible reasons for this statistic having nothing to do with menstruation.
There as well are several credible sources who opine that risk may be increased. These include George Burgess, Director of the International Shark Attack File, and Divers Alert Network (DAN). An article on shark attack in the Feb '02 issue of their "Alert Diver" magazine states: "Although there is no positive evidence that menstruation will increase risk, it is best not to tempt a predator that finds its prey via smell" (p.15). As with Dr. Edmonds' comment, this other position also is without direct research support.
In addition, in the thread cited above by "Walter," http://www.scubaboard.com/showthread.php?s=&threadid=340, you will find several anecdotal reports of menstruating divers being hassled by sharks, and I can provide others if you like. And while we are here, I'd like to expand upon a reference made by Walter within that thread concerning the work of H. David Baldridge & his colleagues back in the 1970s. To the best of my recall, this work in essence demonstrated that sharks prefer fish to mammalian blood, not that mammalian blood isn't of interest to them.
My personal opinion is that there may be a very small increased risk of shark attack related to menses. But, as the risk of shark attack on a diver is already so infinitesimally small, and even smaller on women, it would be extraordinarily difficult to prove the matter one way or the other even if controlled studies were easily done.
This having been said, if I were a woman & was otherwise feeling up to scuba I would not alter my dive plans due to menstruation.
Of course for you hardy ladies diving cold water in drysuits, the whole discussion lacks relevance.
Best regards.
DocVikingo
