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Why Crabs Never Leave Croton on Hudson...

September 9, 2006

What crawls on six legs; has two paddles but no canoe; and has the ability to make a lasting “impression” on residents? You knew all along—the blue claw crab!

Officially the blue crab is Callinectes sapidus Rathburn (Callinectes from the Greek for “Beautiful Swimmer”, Sapidus from the Latin for tasty, Rathburn for the late Dr. Mary J. Rathburn of the Smithsonian Institution who first named the species).

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Croton River Tide Runner: A healthy male blue crab waves at us.

Each year in late spring and summer, blue claw crabs in this area of the Hudson River enter the Croton estuary to mate, spawn and ambush small minnows among the eel grass and milfoil which affords protection from predators. The Croton’s abundance of reeds and grasses and lightly saline water offers the ideal habitat for Blue Claw Crabs.

Male versus Female: Whose side are you on? Females reach maturity at two years old with their last molt, males slightly earlier, which may occur anytime between early summer and late fall. About two days before the female sheds her shell for the last time, a male invariably finds her. Facing each other, the male raises himself on his walking legs to his full height; fully out stretched arms waving; with his rear paddles vertically extended. She will feint left and right and back and forth and up and down, waving red-tipped claws. After this brief courtship ends he will grasp the female with his walking legs face forward and gently carry her waiting the day or two for her to exit her shell.

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Immature female crab belly with the triangular “German helmet” marks emerging.

Upon backing out of her shell in a well protected shady portion of the Croton River for the last time, the female will mate with the male. With the female now very soft and vulnerable to predators, our male friend will stand guard over her with out-stretched legs at his full height, forming a fence, protecting her for at least two days until her shell hardens. The females’ apron now resembles what the locals call a German Helmet or a half circle with a point on the top. It is easy to tell male from female. Males have only blue claws. Females have red tipped claws. Males have an inverted T on their belly (see photo below) versus the half circle or wide triangle on mature and immature females. Grasping crabs by one of the rear paddles prevents a painful pinch, as the crabs arms will not reach your fingers. The rear swimming paddles propel the crab at surprisingly high speed when required; forward, backward, left, right,up,down.

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A white belly shows a newly molted mature male crab with its swimming paddles.

A female crab will release two million or more fertilized eggs into the Croton and Hudson’s ever changing currents. Thankfully, very few survive, for if they all reached maturity each year crabs might crawl out of the Hudson River and seize control of the village with their powerful claws.

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A female’s red tipped claw grasps for prey.

Itching for a Crab? Upon the eggs hatching they enter the world of predators where the microscopic fry float defenseless in the currents. During the first summer the tiny zoeal will undergo seven or eight larval stages, at each stage the baby crab at one-hundredth of an inch will shed their tiny shells undergoing a transformation into a differing creature. At each stage the legs or paddles will under go subtle changes, among other small differences. Flushed from the Croton River by strong freshwater flows from Croton Dam they enter the Hudson to be further sloshed back and forth by the changing tides every six hours. Our residents swimming in the Hudson or Croton Rivers may have experienced a “swimmers-itch” in a sensitive spot after a refreshing river swim. With billions of crab larva in the megalops stage (the second stage of development where the larva have developed tiny claws) in the estuary during summer months, the megalops may be partially responsible for the harmless, and temporary discomfort.

With luck the tiny crabs survive the first summer and bury in muddy sections of the bottom along Croton Point and north along Croton Landing among other locations. They bury face out in the mud during late fall as the river cools slowly and will spend the winter resting. In late spring they emerge from the mud which has protected them and start to grow quickly on the richness the Hudson provides. At this stage they may be two inches from point to point of their shells. Armored by a thick outer covering that contains no living cells, the small crabs quickly out grow their shells. An ever-expanding inner body requires the crab to molt; backing out of the outer shell when it has outgrown the old shell. Over the crab’s life span of about three years this routine may be repeated 18 times or more, with 20 to 50 days between molts, depending on maturity.

How do I measure what is a legal catch? New York State Crabbing Regulations stipulate minimum sizes for harvesting peelers (crabs about to shed their shell), soft shell crabs (those that have shed a shell within the past few days or so) and hard shell mature adults. The DEC harvest regulations are changing for 2006-2007 with new minimum sizes for each life cycle stage of crab to ensure enough mature adults survive.

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How to measure a blue crab? From horn to horn: this male is over 6 inches.

How can I tell how long a crab has been in its shell? The longer since its last molt, the more meat within the crab’s shell. With a newly exposed soft as skin covering, the newly molted crab is highly prized prey for ravenous bluefish and striped bass. Over three days the new covering will harden into the familiar hard shell. Rivermen spot newly molted crabs by several means, knowing the crab will be empty of most flesh. A fresh white belly and apron with clean shell is the key to a newly molted crab.

A dirty, scuffed belly and apron with moss growing on the underside of the outer top shell signals a crab full of sweet flesh.

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A mature male whose scuffed shell is almost ready to molt and full of crab meat.

What is a good way to cook crab? An old Hudson Valley recipe for cooking blue claws called for a large pot with one inch of boiling water and a tight fitting cover. Add to the boiling water a heaping tablespoon of dry mustard, plunge the live crabs one by one into the pot. Leave space for the cover to fit tightly to prevent the crabs from escaping. After fifteen minutes of cooking, drain and allow the crabs to cool and then refrigerate for consumption later with a few cold beers. Interestingly; the same dry mustard was slathered over fish served up from the Hudson River to cover the taste of fuel oil that at the time contaminated most Hudson and Croton River species. Up through the 1970s, rivermen netting shad and striped bass from Croton Bay in the spring were typically paid half the market value for their catch due to fuel oil contamination. Happily, the Hudson River and Croton Estuary are now much cleaner than 30 years ago. But the legacy of heavy metals lingers on.

Or should we? Sadly, New York State has issued advisories warning of the dangers in regularly consuming locally caught crabs and fish from the Hudson and its tributaries. Heavy metals from upstate plating factories, PCB’s released from General Electric factories. A recent study by researchers at Mt. Sinai School of Medicine in a June issue of the journal Environmental Research reveals that of the 124 individuals participating in the study that have weekly eaten Hudson River fish, eighty percent had twice the level of mercury in their blood as compared to those who had not eaten the fish.

Residents should carefully review the NYS advisories and make an informed decision before consuming anything taken from the Croton or Hudson Rivers, including blue claw crabs, on a regular basis. Moderation is key.

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For more information on Blue Crabs and a wonderful story we suggest reading Pulitzer Prize winning author William Warner’s “Beautiful Swimmers” published in 1972 by Little, Brown and Company and still available in paperback.

— Charlie Kane, Trustee, Village of Croton-on-Hudson.

All crab photos by: A. Wiegman.



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