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Extensive science has demonstrated 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. And, while the research does show that sharks seem to be more attracted to fish than human blood, they most certainly do respond to the latter.
The solid research findings on fresh human, animal & fish blood, other human bodily fluids, including "dead" ones like urine, and a wide variety of water-borne organic chemicals found in such 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.
The claims you see about menstrual blood repelling sharks are not substantiated by any studies that I have been able locate. Those making such claims to whom I have written have not provided any.
Dr. Richard Martin has asserted that "Menstrual fluid does include 'old' (hemolysed) blood, but it has been shown experimentally that sharks are simply not interested in it," but does not give any supporting references.
A brief and uncompelling piece on the topic by Dr. Jacalyn McComb 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 & collegues 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, and it most assuredly does not meaningfully support Dr. McComb's contention.
So much for detection/attaction. As to any increased risk of shark attack during menses, to the best of my knowledge there is no research on this.
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. Martin's and Dr. McComb's comments, this other position also is without direct research support.
In earlier threads on the subject within this forum, you will find anecdotal reports of menstruating divers being hassled by sharks, and I can provide many others if you like. Of course, such reports are a very weak form of argument as far as science is concerned.
As you can see, as with much in scuba, research and the "experts" really haven't settled the issue as yet.
My personal opinion is that there probably is a very, 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 divers, 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 safe 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
The solid research findings on fresh human, animal & fish blood, other human bodily fluids, including "dead" ones like urine, and a wide variety of water-borne organic chemicals found in such 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.
The claims you see about menstrual blood repelling sharks are not substantiated by any studies that I have been able locate. Those making such claims to whom I have written have not provided any.
Dr. Richard Martin has asserted that "Menstrual fluid does include 'old' (hemolysed) blood, but it has been shown experimentally that sharks are simply not interested in it," but does not give any supporting references.
A brief and uncompelling piece on the topic by Dr. Jacalyn McComb 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 & collegues 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, and it most assuredly does not meaningfully support Dr. McComb's contention.
So much for detection/attaction. As to any increased risk of shark attack during menses, to the best of my knowledge there is no research on this.
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. Martin's and Dr. McComb's comments, this other position also is without direct research support.
In earlier threads on the subject within this forum, you will find anecdotal reports of menstruating divers being hassled by sharks, and I can provide many others if you like. Of course, such reports are a very weak form of argument as far as science is concerned.
As you can see, as with much in scuba, research and the "experts" really haven't settled the issue as yet.
My personal opinion is that there probably is a very, 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 divers, 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 safe 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
