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What’s Happening:  Snow and Tanner Crab Growth Study, Dutch Harbor, Alaska, 2016

April 27 to April 29

We have molting crab!

Below are a few examples of Tanner crab that have molted.
Note: all photos credit NOAA Fisheries.  Click photos for enlargements.

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Both photos above show a crab in the process of molting by backing out of its old shell.
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Jeff Cox (Bering Sea Fisheries Research Foundation) is checking for molted crab in condos.
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  April 21
  April 19-26
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  April 27-29
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  May 13-17
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The photos below show crab that have successfully molted, and their old shells.  Learn more about each crab below.

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Top: new shell (after molt). Bottom: old shell (before molt).  Note that the crab post molt is missing one leg, you can see it got stuck in the old shell during the molting process.  By losing the leg the crab can still survive molting, and the leg can be regenerated through future molting events.

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Top: old shell (before molt). Bottom: new shell (after molt).  The juvenile female molted into a mature crab.  Notice that the juvenile crab has an abdominal flap that only covers about two-thirds of the ventral surface.  The mature crab has a circular abdominal flap that covers most of the ventral surface.  Female crabs hold eggs on the pleopods, which are attached to the inside of the abdominal flap.

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Top new shell (after molt). Bottom: old shell (before molt).
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(same crab as left photo) When a crab molts, it sheds its shell and all the chitinous linings of various structures, including the gills, digestive tract (esophagus, stomach, ‘intestines’) and portions of the reproductive tract.  This is a picture of of the inside of a shed, molted shell (the exuvium).  The feather-like structures are the shed chitinous lining of the gills.
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Here is a newly molted crab in a condo.


By Vanessa White, NOAA Fisheries scientist

Vanessa White
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