BIOLOGY AND NATURAL HISTORY 207 



one of the phenomenal developments of the fisheries industries of the coun- 

 try. They are almost exclusively confined to the Chesapeake, South Atlantic, 

 and Gulf regions. 



DISTRIBUTION 



The blue crab occurs in most estuarine waters from New York to Texas. 

 While more crabs have always been taken from Chesapeake Bay than from 

 other areas of our coast, the commercial yield from South Atlantic and Gulf 

 regions has been steadily increasing, suggesting a natural abundance of 

 crabs in these waters far greater than hitherto known. Unlike its relative, 

 the shrimp, the blue crab is only occasionally found in the open sea off 

 North Carolina, as elsewhere, but prefers shallow bays, sounds and river 

 estuaries, where it thrives in waters ranging from ocean saltiness to brackish 

 or even fresh. However, it is recognized that heavy freshets in coastal 

 streams, such as the Neuse and Pamlico rivers, often drive crabs out of the 

 rivers toward the more saline waters of Pamlico Sound. Blue crabs usually 

 seek shallow inshore areas in warm weather and retreat into the deeper 

 channels in winter. 



NATURAL HISTORY 



The life history of the blue crab is best known in Chesapeake Bay be- 

 cause the fishery there has been long established, and extensive biological 

 research has accordingly been undertaken. However, the general features of 

 the life history are probably quite similar in all sections of the coast. 



Each year between April and August a new generation of blue crabs is 

 produced in North Carolina. Sometime during this period the adult female 

 or sook crab extrudes from i>4 to 2 million eggs, each egg about Yioo inch 

 in diameter, and these together form a large mass known as the sponge, 

 which is firmly attached to the abdomen of the crab. The eggs hatch in 

 about 15 days in the saltier waters adjacent to the inlets and ocean. Sub- 

 sequently, a second sponge of eggs may be produced in the same season by 

 the female crab. The newly hatched crabs are quite unlike their parents in 

 appearance; they pass through two stages of metamorphosis in neither of 

 which do they have any recognizable resemblance to adult crabs as we know 

 them. The first of these is called the zoea, about ^5 inch in size, free- 

 swimming or drifting about helplessly in the water. The zoea molts several 

 times, believed to be six, and is transformed at its last molt into the next 

 stage, the megalops. This stage, no larger than the first zoea, about ^5 inch, 

 begins to take on at least a little more resemblance to the crab as we know 

 it; at the megalops' first and apparently only molt at about one month after 

 hatching of the egg, it becomes a crab in general appearance, and settles to 



