Turtle Journal

Don Lewis Studies Two Tiny Juvenile Horseshoe Crabs

The Turtle Journal team revisited our “secret” horseshoe crab nursery on Thursday afternoon.  We last checked this spot on April 18th; see Salt Marsh Awakening: Juvenile Horseshoe Crabs Active on Outer Cape Cod. 

Rufus Examines Tiny Juvenile Horseshoe Crab

We wanted to get a sense of how well these ancient creatures may be doing, particularly in this long, chilly Spring.  In the decade we have been checking this location each Spring for juvenile horseshoe crabs, we have never before seen so much activity.

Three Tiny Juvenile Horseshoe Crabs

Dozens of juvenile crabs from tiny to small to mid size bounced around the salt marsh tidal pool like Tonka Toy bulldozers plowing through a playground sandbox.

Juvenile Horseshoe Crabs Bulldoze Serpentine Mazes

We can only laugh at their antics as they carve serpentine mazes in the oozy bottom.  Adult horseshoe crabs are beneficial auto-tillers of tidal and subtidal zones, a skill they obviously seem to practice from birth.

Juvenile Horseshoe Crab Left Compound Eye

The exceptional compound eyes of horseshoe crabs never cease to amaze us.  Much of our knowledge about human eyesight came from studies of these compound eyes.  Dr. H. Keffer Hartline received the Nobel Prize for his research on horseshoe crab vision in 1967.

Two Tiny Juvenile Horseshoe Crabs in Nursery

While documenting the science of this horsehoe crab nursery is rewarding per se, we confess that watching these juveniles spin around the tidal pool like pre-teens driving their first amusement park bumper cars can be mesmerizingly delightful.  So much so that you forget that you’re even doing science.

Rufus Discovers First Spawning Horseshoe Crabs

The Turtle Journal team patrols SouthCoast beaches each morning throughout the Spring season.  This morning, as Sue Wieber Nourse and Rufus the Turtle Dog walked a Buzzards Bay barrier beach, they spotted pairs of spawning horseshoe crabs scatter along the shoreline in the morning high tide. 

Spawning Horseshoe Crab Pair (Female in Front)

This morning’s ~ 7:30 am high tide brought the first evidence of spawning horseshoe crabs this season.  The pair above well illustrates a spawning pair.  The larger female is in front with the smaller male grasping onto her shell, so that he can be Johnnie-on-the-spot when she deposits her eggs along the tide line.

Spawning Horseshoe Crabs on SouthCoast Barrier Beach

Sue has been observing these SouthCoast barrier beaches for many years now as principal of Turtle Journal and formerly as director of Tabor Academy’s Marine Science Center and as inaugural holder of the Jaeger Chair for Marine Studies.  She reports that today’s spawning burst, while only containing a handful of crabs, still represents the largest number of specimens she has yet seen in this location.  Horseshoe crabs had nearly been extirpated on the SouthCoast by harvesters who chop them up for cheap whelk bait.

 Rufus Guards Stranded Torpedo Ray in Truro

With a southwest breeze blowing across the bay, Turtle Journal’s Sue Wieber Nourse and Rufus the Turtle Dog drove out to Truro on Outer Cape Cod to see what might have been pushed ashore with the morning’s 11.5-foot tide.  In the bright sunlight, they patrolled Duck Harbor in Wellfleet and Ryder in South Truro with great joy, but few discoveries. 

Female (Electric) Torpedo Ray at Fisher Beach in Truro

Then, an eighth of a mile north of the landing at Fisher, they encountered a female electric Torpedo Ray that had washed ashore.  Turtle Journal has found torpedo rays stranded along the Cape’s bayside beaches in the fall as we search for cold-stunned sea turtles.  (See Shocking Discovery!  Torpedo Ray in Wellfleet Bay.)  Torpedo rays have anterior organs that can generate and discharge 220 volts to stun a prey … and to keep predators like human researchers at a respectful distance.

Section from Left Electrical Organ of Large Torpedo Ray

The torpedo ray has two kidney-shaped electrical organs that make up 20% of its weight and are located on the pectoral fins. They generate a power equivalent to 220 volts that stuns prey with a burst of electric current. Its prey includes flounder, silver hake fish, small sharks such as dogfish, eels, worms and crustaceans. After stunning its prey, the torpedo ray guides food with its pectoral fins toward its protruding mouth for ingestion.

Rough Field Measurements of Torpedo Ray in Truro

Without a full scientific kit on hand, Sue managed with the tools we wear on our feet for a rough field measurement of specimens.  This female measured approximately four feet long and three feet wide, and seemed in relatively good shape.  Turtle Journal informed the Wellfleet Bay Wildlife Sanctuary of the specimen’s location, so that a follow-up necropsy could document the specimen and possibly determine its cause of death.