The Unexpected — 23 December 2000

If it’s the unexpected that keeps naturalists energized when conditions would dictate a good book and a raging fire, then I guess I hit jackpot this afternoon.  Temperatures hung in the twenties with sustained 25-knot winds whipping across the bay from the northwest.  The wind chill plunged to zero and below, and several feet of slush ice had formed at the intersection of the channel and the shore.  The last thing I would expect to encounter, other than a stone-cold terrapin of course, would be a live horseshoe crab.  Yet, here was an adult male, sporting a decorative colony of parasite shellfish and burrowed into the low tide exposed beach off Lieutenant Island’s north shore.

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Live, Exposed Horseshoe Crab in Sub-Freezing Temperature

Last season began an important research program on the Cape to formally study our native horseshoe crab population.  In the face of substantial harvesting of these critters for biomedical purposes, as well as for conch and other fishing bait, we felt obliged to nail down some concrete data to underpin any future policy changes.  As part of this project, nearly a thousand adults were tagged to study migration and behavior and physiology, and to obtain a rough population estimate through capture-mark-recapture efforts over a number of years.

As I patrol wrack-strewn beaches and marshes in the study area, I routinely examine molted shells and horseshoe crab remains, which wash ashore with the tides, to see if they are marked or not.  So, this afternoon at dead low tide as I walked the shoreline and spotted a horseshoe crab shell, I stopped to check it.  I realized at once that this one was quiet alive and had dug itself into the beach sand about two feet from the receding tide line.  I flipped the crab over to determine gender and its reactions were anything but sluggish.  It seemed to move as normally as in the summer.  I saw that he had the telltale “boxing glove” clasper at right front, but the end of the left “boxing glove” appendage was missing.  On his back, the tail immediately went into action to right himself.  I saved him the trouble and returned him to his repose, reburying his shell with moist beach sand.

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Male Horseshoe Crab with “Boxing Gloves”

What the heck a horseshoe crab was doing out of his hibernacula in these conditions is beyond my ken.  But it’s these little surprises that keeps us outside our winter hibernacula, too.

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