SEA 



SCIENCE 



FEMALE BLUE CRABS: 



MOLTING, MATING AND MANAGEMENT 

 MOLTING 



Throughout their lifetimes, immature female crabs, or "sallies," and 

 male crabs, known as "jimmies," will molt approximately 21 to 23 times, 

 says Steve Rebach, associate director of North Carolina Sea Grant. 



Larger adults molt less frequently than smaller juveniles, notes Dan 

 Rittschof, a blue crab researcher from Duke University. As adults get big- 

 ger, it takes more energy to produce muscle, he explains. 



MATING 



A sally has a distinctive triangle shape on her abdomen, but the 

 triangle will turn dark purple when she reaches sexual maturity and 

 undergoes one final molt. 



After this last molt, she emerges with a U-shape on her abdomen. 

 She is now a "sook," or sexually mature female, and most of her energy 

 will be directed toward egg production. 



As for her male counterparts, Rittschof says they probably also 

 stop molting at some point, "but there are no massive morphological changes like females," he 

 explains. 



A sook will mate almost immediately after her final molt, while her shell is still soft. 

 Although a sook only mates once, she internally stores packets of sperm to fertilize multiple egg 

 clutches throughout her lifetime. After fertilization, she carries the eggs for two weeks until they 

 hatch. 



MANAGEMENT 



Despite extensive research on blue crab molting and mating, female migration patterns 

 remain somewhat mysterious, says Rittschof. 



Through an N.C. Blue Crab Research Grant, Rittschof is conducting a four-yearfield study 

 near Beaufort Inlet regarding female blue crab migration patterns and reproductive potential. 



In late spring, females carrying fertilized eggs - known as sponge crabs - ride outgoing 

 tides from low-salinity estuarine waters to high-salinity ocean waters, where they release their 

 eggs. 



People used to think that sponge crabs had orte clutch and died, but that isn't true, 

 explains Rittschof. 



A female in North Carolina waters can have up to five dutches during the May to 

 September spawning season, he says. And if they don't get caught up in crab pots or eaten by 

 predators, females can live and spawn for another two or three years. 



As for migration patterns, Rittschof s research has debunked some myths about female 

 blue crabs. 



"The existing lore is that crabs go to the ocean, have their clutches and go home," he says. 



But Rittschof s tag-and-recapture data, coupled with offshore recapture data from 2002, 

 suggests that a substantial number of females live offshore for extended periods. 



"Crabs that spawned in the fall don't die, but I don't know where they go," he says. 



Rittschof has marked 1 2,000 female crabs near Beaufort Inlet, and although he believes 

 some returned to estuaries after spawning season, none have returned to the estuary where 

 they were tagged. 



"The crabs don't know where the estuary and the ocean are," he says. "They ride the 

 tide." □ - K.A. 



Sponge crabs display a series of egg development. 

 Each number represents the day of development. 

 The sponge color changes as the yellow yolk is 

 absorbed by the embryos. 



"soft crab" stage, has made blue 

 crabs famous. Often referred to as 

 "soft shells," the sweet, white meat 

 from these crabs is a seafood delicacy 

 recognized throughout the world. 

 Popularity is not without its price, 

 however; the ubiquity of the "soft shell" 

 moniker has caused many to mistake 

 soft crabs for a separate species. 



For the next two to four days, 

 the crab draws on the inorganic salts 

 stored during the premolt stage to 

 harden its new armor. Finally, the crab 

 begins replacing the water in its tissues 

 with muscle-building protein. 



The crab will live in its roomy new 

 exoskeleton for a while, but in 1 4 to 50 

 days — depending on the crab's size 

 — the shell will become too snug. Then 

 the whole process will begin again. 



Besides being a high-stakes 

 benthic drama, blue crab molting 

 might also find its niche in reality 

 television — radical makeovers that 

 result in newer, more fit and desirable 

 individuals. □ 



COASTWATCH 25 



