198 MARINE FISHERIES OF NORTH CAROLINA 



adults, although recent hydrographic researches may shed some light on this 

 interesting problem (see below). 



The distribution of the larval stages yields certain key information about 

 the natural history of the species. Pearson found eggs of P. setiferus off the 

 Louisiana, Georgia, and Florida coasts, in limited numbers in St. Augustine 

 Inlet but only on flood tides, and not in inshore plankton tows. The distribu- 

 tion of the larval stages agrees generally with that of the eggs, the only 

 inshore record being that of three myses taken at St. Augustine Inlet. During 

 May and June maximum seasonal numbers of post-larvae are found at 

 inlets where flood tides sweep them into brackish nursery areas. Here they 

 adopt a demersal life and commence feeding on bottom organisms. Growth 

 of post-larvae is rapid, increments in length of P. setiferus as great as 29 

 mm. (1-1/6 inch) in 43 days being recorded in aquaria by Pearson (1939). 



ADULTS 



The growth which follows larval development is accompanied by regular 

 migration back toward deeper water of high salinity. Weymouth, Lindner, 

 and Anderson (1933) state for P. setiferus, the common white shrimp: 



During July, at an average length of about 99 mm (4 inches), they (shrimp 

 from eggs laid during the preceding spring) enter the commercial catch, ap- 

 pearing first in bays, creeks and other ''inside" waters and later outside. 



They continue in the fishery furnishing all of the fall catch with its peak in 

 October until the following spring and summer, when the survivors spawn and 

 disappear at the age of one year. By late fall they have reached a length of 

 about 120 mm (4% inches) which they maintain during the winter. Resuming 

 growth in the spring, they show a rapid and striking differentiation in the size 

 of the sexes and spawn at lengths of 130 to 170 mm (5^^ to 6% inches) for the 

 males and 135 to 190 mm (5^ to 7^ inches) for the females. Their fate is un- 

 known, but their complete disappearance from the fishery is undoubted. 



The breeding season is characterized by (i) development of the sex organs; 

 (2) a rapid differentiation in size between the sexes; (3) a difference in the 

 behavior of the sexes so that the proportion of sexes, uniform during the winter, 

 shows wide fluctuation. Far more mature shrimp of both sexes are found out- 

 side than inside the sound. 



The shrimp is most abundant in shallow coastal waters near river mouths or 

 deltas. 



This summary outline is based principally on length-frequency data ob- 

 tained chiefly in Georgia by examination of thousands of shrimp during a 

 period of 19 months in 1931 and 1932. 



Burkenroad (1934) interprets the disappearance of year-old shrimp 

 from the coastal feeding grounds as a spawning-migration to waters farther 

 offshore. He points out that disappearance of mature adults occurs without 



