I do not mean to single out Jack - he is a fine person, writer, and waterman. But this post is a continuing example of confusion on this topic and it needs to be cleared up and disposed of.
The fish didn't get her when she [shed] on the last full moon...
Kindly indulge my continuing effort to disabuse you of this fantastical connection between a moon and a shed. Let's examine this step-by-logical step:
1. Crabs do not shed in winter. To those of you who will claim something like, "oh they can't see the moon..." there is a simple reply:
a) How do you know they cannot see winter moonlight? Crabs burrow into the mud in the winter months but their antennae, eyes and mouthparts remain slightly above the surface bottom to maintain gill circulation. In the clear, cold, winter water some light would penetrate. Do you seriously imagine that a wintering crab "sees" a full moon, jumps up, and sheds her shell?
b) As noted below, molting begins two full weeks before the shell is shed. Do you seriously imagine that a wintering crab is sitting on the bay floor, observing the lunar cycle, and anticipating the full moon?
Of course not, crabs do not shed in winter because they are in a hibernation state and their growth rate is slowed or stopped. Therefore the moon can have no effect.
2. From a reproductive standpoint, it would be impossible for all or even most crabs to be shedding simultaneously. Since the female must be in a post-molt soft state to mate, the male by definition must be...er...in a hard state. Jokes aside, the male must possess a hard shell as he mates and protects the soft sook while fertilization takes place. If at every full moon every crab were molting, mating would never take place and the species would soon go extinct. Therefore the moon can have no effect.
3. Crabs do not suddenly molt; there are several physiological steps that take place before the final molt. For example, the preparatory "white sign" appears two weeks prior to molt. There are at least three possibilities for this development:
a) there is a biological imperative (i.e. the crab is growing) and a hormonal/mechanical process intitiates.
b) the crab "knows" that a full moon will appear in two weeks, and the crab begins her undressing process 14 days before the ball.
c) assuming the moon has anything to do with molting, since we have learned that molting begins 14 days prior, perhaps it is the waxing moon to blame for the molt, and not the full moon.
Which of these three, a), b), or c), do you seriously believe is actually the cause of molting?
4. It is an indisputable fact that even during the full moon, you can catch crabs in all states of shell hardness. Therefore, the moon cannot be the sole influence (if at all) on crab molting.
5. It is an indisputable fact that crabs shed at different rates depending on age and size. [Jack and others with fish tanks can easily test this: place one, two, three, four, five and six-inch crabs together and observe rates of molting. Of course, there is the risk of cannibalistic
crustaceicide with this arrangement, so try the experiment in separate tanks if possible.] Of course, this homemade observation is unnecessary as the literature is clear on this point: the molting rate is an energy-dependent process which is only begun as a physiological imperative, i.e. the crab would not survive unless he grows into a new shell. This happens weekly when young, and bi or tri-monthly when older. Therefore, the moon can have no effect.
6. Even assuming the lunar theory, what can the cause possibly be? What evolutionary process could have caused the blue crab to gain an advantage by shedding on the full moon? If you believe the reflected light is the answer, why would a crab wish to expose his soft shell to predators, including other crabs, when the night light is brightest? Crabs try to hide when molting, maximum exposure would be fatal rather than protective. Well, maybe you imagine there is some gravitational cause...but you forget that the moon is always there regardless of how much light is reflected and whether you can see it or not. The gravitational attraction between a 4 oz. crab and the lunar body approx. 239,000 miles away is effectively a constant zero. Therefore, there can be no lunar gravitational effect on crab molting.
7. You have neglected to consider the most likely answer to this delusion: the
anthropocentric fallacy which causes all of us to mistake our biased observations for causality. We see the small proportion of crabs in our traps, pots, pilings which are shedding; we do not see the millions of others which are not shedding. Like primitive peoples who thought that their dances brought rain and didn't realize that their propitious storm formed many days prior and many miles away, we forget that crabs begin molting two weeks before the full moon peeks out (there is an example of anthropomorphism - the moon doesn't "peek" even if we like to imagine it does). We see more or fewer crabs in the traps, and imagine all sorts of reasons why this is so: rain or no rain, luck or lack of it, wind or no wind, a moon with more or less sunlight bouncing off it. All of these old wives' tales can be fun to bandy about, but there comes a time when grown men have to accept reproducible scientific tests, facts, and observations - and to bequeath the fables to the simple, the gullible, and Tattoo.
