Copyright © John Page Williams Jr. All rights reserved.
Definitions for this episode:
Peelers: hardshell blue crabs that are showing signs of molting.
Sloughing (pronounced "sluffing"): also called molting and shedding, when a crab sheds its rigid outer shell to allow its body to grow.
Soft crab or soft-shell crab: a blue crab that has shed its rigid outer shell, their skin is still soft and they have not yet regrown a new hard exterior shell.
This is John Page Williams with another reading from Chesapeake Almanac. This is June and the title is "For Soft-Crabbers, Summer Is a Busy Season."
Louis Whittaker's life is just getting back to normal, if a soft-crabber's life can ever be said to be normal during the season. The first big run of peelers comes on the full or new moon in mid-May. It means traps that are 2 and 3 feet deep in crabs, shedding tanks full to bursting, everybody working heavy overtime. The early seaon is like a sprint. Summer means settling into the rhythm of a marathon.
Louis runs Sea Products, Incorporated, in Reedville, an innovative soft crab operation with shallow indoor shedding tanks. From May until late September, his life and the lives of his family are dominated by crabs sloughing (shedding) their shells.
Baywide, everyone in the industry is getting into the summer routine. Whether using closed-circuit shore tanks, flow-through tanks with pumps, or traditional overboard floats, in season a soft-crabber is always busy, and sometimes extremely busy. There are crabs to be caught, certainly a major task. Then there are the floats or tanks to be cared for. "Dipping up" is a several-times-daily ritual, removing newly shed soft crabs, their sloughs (or empty shells), and any peelers that may have died in the process. Finally, there is the business of cleaning, packing, freezing, marketing, and shipping.
Crabs don't molt when the water is cold, so the first run in spring is a good one. There are lots of peelers, and shedding survival is high. But crabs must continue to slough as they grow. Later in the summer, as the water warms, a larger percentage of crabs will "hang up" and die in the process of shedding: in conventional floats, late summer survival can be less than 50 percent. High water temperatures drive out oxygen from solution and a crab's oxygen demand, while it's sloughing, goes up something like 6x (6 times or 600 percent). A good spring run can make the difference between profit and loss for the year, so soft-crabbers give it their best efforts, but they work hard all season to keep survival as high as possible.
Molting, or shedding an entire shell, seems like a bizarre way to grow, but it is common in the crustacean world. And it is not simply a periodic event in the life of a crab. During a 24- to 36-month life span, the animal will molt more than 40 times. At first, shedding comes every five days or so, when crabs are young and small. Gradually the interval lengthens to over a month as the crab matures. In the period between each shed, it must regain its strength, fill out its new and larger shell, and build up its energy reserves before the actual molting process begins anew. There is very little time in a crab's life when it is not concerned with some aspect of shedding.
The process begins when nerve receptors inside the shell signal the crab's central nervous system, which controls a series of hormones—basically chemical signals—in the blood. These cause the cells at the base of the shell to separate from the shell itself. Nerves attached to sensory receptors in the shell begin to retract. The base cells form a new shell inside the old one. It is this new shell that shows up as the white, pink, or red sign that crabbers look for on the next-to-last segment of the swimming leg on a peeler.
The shell is a complex structure with several different layers that give it strength and its characteristic colors. It is made up primarily of protein and chitin, the latter a complex fibrous carbohydrate that is the crustacean equivalent of cellulose fiber in wood. Between the old shell and the new one is a layer of mucus.
When the new shell has developed, some of the material in the old shell is reabasorbed at critical points like the bases of the limbs, to soften the potential bottlenecks in the molting process. By this time, the crab has ceased feeding, hidden itself as best it can, and begun to drink large quantities of water. The water causes the animal to swell and split its shell along the back line between upper and lower sections. Hence the nickname "buster" for this stage. Now the animal begins to back out of its old shell, with the mucous layer providing lubrication.
This is a critical time for a crab, especially a big one in warm water. It is wriggling out of everything, even its old gills, mouth parts, and antennae. The new gills cannot function for a time, but once they begin to work, they must supply the crab with plenty of oxygen so it can complete the process. And since warm water holds less oxygen than cool water, summer molts are especially risky, both in the wild and in the crabber's tanks and floats. A major advantage of the shore tanks at Sea Products is their ability to keep the water well oxygenated even in late summer.
Once the crab is free of its old shell (assuming it is not caught and eaten by an eel, a raccoon, a rockfish, a human, or any of the other animals that appreciate it), the cells at the base of the new shell go to work again. They extract calcium from the blood and secrete it to the outer shell. Within a matter of several hours, the calcium mineralizes the chitin-protein structure, giving it the consistency of parchment, hence the nicknames "papershell" and "buckram" given to crabs at this stage. Within 48 hours, the shell is hardened. The crab begins filling out its new shell and getting ready for its next molt.
Vertebrate growth processes are complex, and it is always exciting to watch babies and puppies and ospreys and rockfish grow up. But there is a special drama to walking a marsh at dawn after a full moon and finding the bank littered with sloughs, or catching a buster, putting it into a bucket, and watching it shed. Even a veteran soft-crabber like Louis Whittaker smiles wh he has a chance to watch it.
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