Do female dolphins menstruate like other mammals? If so, why aren't they killed by sharks being attracted to their blood?

Oh, well, I'm talking about menstruations so often that on some ocassions I jest with the idea of recalling the blog vadereglas instead of vadebichos.
This is another approach to the matter of menstruation in mammals. I find this topic of menstruations not only interesting and important but also poorly investigated and explained so far. While docs continue telling that only women menstruate and there are only two models of reproductive cycles in  placental mammals, with or without menstruations, scientific proofs against this dualistic model are acumulating. So an urgent revision of this dual model (estrous cycles versus menstrous cycles) is needed, and a more generalistic view of the different cycles mammals have.

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Dolphins don't menstruate, however they bleed during labor. There is no data about how they manage to avoid sharks attacks, but it is a good question:

 They don't menstruate, I mean that they don't spell menstrual blood through their vaginas. I'm being very graphic in order to be very clear.
But there is a especially delicate moment when they do bleed, the delivery, as you may have guessed. I'm afraid that I don't know how they manage to avoid sharks attacks, as far as a few as almost none wild dolphin labor as been documented.  But it is a very reasobable question.

Image from http://imgur.com/gallery/fvJ1UfN, however i would like to know the author to give them credit. Love the vision of actual blood in this image of a dolphin labour.

Although female marine mammals don't mentruate, other mammals, besides women, do: 

 Coming back to menstruations and female mammals, generally speaking there are two different types of reproductive cycles called estrous cycles and menstrual cycles. Although they differ in a number of characteristics, the most significative one is that females with menstrual cicles shed the endometrium during the menstruation if they haven't became pregnant, while femaless (lucky them) with estrous cycles reasorb it or just maintain it.While it's very commonly believed that  many mammals menstruate, menstruation is only found in a few disparate  mammalian groups. Humans, other apes, and Old World monkeys menstruate.  (These groups form clade Catarrhini.) Some other primates may  menstruate. Although some scientists opine that only primates mensturate basing it in a very narrow vision of this phenomenon, menstruation has been found in four bat species in  two bat families, Phyllostomidae and Molossidae, and elephant shrews/sengis, relatives of elephants and aardvarks.

However, only women menstruate so copiously. Menstruation is such a great taboo that very few scientists have wondered how early women could cope with it in a enviroment full of predators. And none has answered this question.
But menstruation is only copious in human females.
I suffer my own bunch of problems related to menstruation, as many other women do. Due to them I have wondered many times how was it possible for early women to cope with abundant blood discharges in an enviroment full of predators, with the logical danger of attracting them.
I have not found any paper related to it. It seems that it is not a matter many investigators have thought worth to be studied.
There are tones of anthropological papers that describe ad nauseam customs related to menstruatio in tribal people, such as mentruation huts, celebrations of first menstrual bleed, etc. But they don't get into describing if those menstruations are abundant, painful or regular.
I have discussed these items with a friend who is also interested in menstruations, I have kinda of scientific background while she is more on the multicultural perspective. She said to me that some of her African friends, who have a totally different diet from ours, have reported her that they menstruate every two or three months (instead of monthly) and that their menstrual bleed is by no means so copious as ours. And they are fertile.

In my opinion, mentruations shouldn't be so copious or painful at all. It is an indicative that something is wrng in our lifestyle and many women are suffering for it. Menawhile this seems to follow unnoticied, talking about menstruation is minded as disgusting and even sceintits are unable to break the enourmous taboo we have with it.