m a r i n e advice 



Shedding Beyond the Water's Edge 



Crab shedding in North Carolina 

 has come a long way. Used to be, 

 most pre-molt crabs were held in 

 sunken boats or floating trays offshore 

 while crabbers waited for the critters 

 to bust out. 



Though operation was inexpen- 

 sive, access was difficult, lighting was 

 non-existent and rough wave action 

 often interrupted the shedding process. 



Fishermen eventually built 

 onshore tanks on legs at a comfortable 

 height for fishing the trays. They 

 installed lights so they could work 

 through the night. Water plumbed 

 from a nearby creek or sound supplied 

 a fresh flow to sustain the crabs. 



Sea Grant marine agent and crab 

 expert Wayne Wescott says a little 

 more than 90 percent of crab shedders 

 in the northeastern part of the state 

 now use this flow-through method. 



But not all coastal entrepreneurs 

 have waterfront property. And the 

 ones that do don't always have good 

 water quality. 



With new technology perfected by 

 Wescott, folks who live along water- 

 ways clouded with silt can shed crabs 

 simply by installing a swimming pool 

 filter in their flow-through system. 

 And through the science of closed, re- 

 circulating systems, inland coastal 

 residents can shed crabs in their 

 backyard. 



"We could shed crabs on top of 

 the Empire State Building if we 

 wanted to," says Wescott, who has 

 been shedding crabs for almost 40 

 years. 



Of course, you need a body of 

 water within reasonable distance from 

 your shedding facility to ensure a 

 healthy and abundant supply of crabs. 

 But the technology improved by Sea 

 Grant over the past few years has 

 offered more North Carolinians a 



piece of this $12 million pie. 



Most closed, recirculating 

 systems use reservoirs, shedding 

 trays, mechanical filters, biological 

 filters, protein skimmers, pumps and 

 plumbing to provide suitable water 

 for crab shedding. 



"We learned that if we used water 

 over and over, we had to do two 

 things," says Wescott. "We had to 

 provide oxygen so that the crabs 

 didn't suffocate, and we had to 

 provide something to absorb crab 

 waste, which is minimal since they're 

 not eating much." 



Crab waste produces ammonia, 

 which is toxic to the creatures. 

 Wescott determined that placing 

 rocks, oyster shells or small plastic 

 shells in the reservoir encouraged the 

 growth of bacteria. These bacteria or 

 "bugs," as Wescott calls them, feed 

 on the ammonia, converting it to 

 nitrite. 



Another bug is introduced to feed 

 on the nitrite, which can also be 

 poisonous to the crabs. The nitrite is 

 converted to nitrate, which is less 

 toxic. 



"Because it is a food supply for 

 something, these things flourish, but 

 they also must have oxygen to 

 flourish and do their jobs," he says. 

 Aeration in flow-through and closed 

 systems reintroduces vital oxygen to 

 the water. 



Closed systems draw on a 

 reservoir of seawater, real or simu- 

 lated; groundwater; or other 

 nonchlorinated water. The salinity 

 should approximate that of the area 

 from which the crabs are harvested. 



But crabs can even be held in well 

 water, provided the peelers used in 

 the system were taken from waters of 

 low salinity. Working with commer- 

 cial shedders, Sea Grant developed 



this system, which uses cool ground- 

 water and heating elements to 

 regulate water temperatures. 



Because they are high-mainte- 

 nance, closed systems are recom- 

 mended only if there is no alternative. 

 Wescott estimates that less than 3 

 percent of shedders in Dare County 

 are using closed systems, and most 

 are small operations. 



"A closed system is the worst one 

 possible, but it works," he says. 



In the past decade, soft crab 

 production in the state has jumped 

 from a reported 88,000 pounds, 

 valued at just under $200,000, to 

 more than 2 million pounds, worth 

 about $6 million. Yet demand still 

 exceeds supply. 



Wescott has opened another 

 avenue for the industry along miles 

 of previously unusable waterfront. 

 Poor water quality has prevented 

 shedding in areas where wind, rain, 

 runoff and boat traffic cause excess 

 turbidity. 



Suspended materials in this water 

 clog the gills of crabs held in shed- 

 ding trays, causing high mortality. 



After he installed a filter to keep 

 sand out of his swimming pool, 

 Wescott wondered if the same 

 technology was applicable to shed- 

 ding crabs in muddy water. 



"So I got to talking with 

 (Collington crab shedder) Murray 

 Bridges, and he decided he'd try it," 

 says Wescott. "It worked like a 

 charm." 



Use of a pool filter also prolongs 

 the effective holding time of peelers 

 in waters of marginal quality. 



Sea Grant has developed several 

 publications on these alternative 

 shedding methods. For more infor- 

 mation, see The Bookstore, page 25. 



Carla B. Burgess 



20 MAY/JUNE 1992 



