BIOLOGY AND NATURAL HISTORY 201 



feet or may, if it be near the surface, result in repeated and haphazard back- 

 ward leaping from the water. Except when alarmed, shrimp swim forward. 



Although usually found on the bottom, shrimp do swim near the surface, 

 often at night. The effectiveness of the night trawl and channel net (see 

 above) depend upon the shrimp's presence at or near the surface. 



The conditions under which shrimp bury themselves in the mud have not 

 been studied, but this phenomenon is mentioned by Weymouth, Lindner, 

 and Anderson (1933) and reported by oystermen and clam diggers in 

 Pamlico Sound, where specimens, presumably from the mud, can be 

 collected during the winter months. Examination of these "mud-shrimp" 

 reveals a high percentage of P. duorarum. 



DISCUSSION 



Since most of the published information regarding shrimp is based on 

 observations made largely in the Gulf of Mexico and almost entirely outside 

 of North Carolina, application of the present knowledge to local conditions 

 presents certain problems and leaves many questions unanswered. The fish- 

 ing season for P. setiferus in North Carolina agrees generally with that 

 listed by Weymouth, Lindner, and Anderson (1933). A slightly earlier dis- 

 appearance of this species suggests a southward migration as reported by 

 Higgins (1937, '38, '39, '40). Specimens of P. setiferus measuring 150 to 

 190 mm. in length are taken frequently in the fall. These must represent 

 shrimp spawned during the preceding year (see section on adults, above) 

 and are probably migrants from farther south. The spring run of P. setiferus 

 most certainly is made up of ripening individuals entering the local waters 

 from outside the State. The disappearance of these shrimp in early summer 

 seems to be a spawning migration. The possibility that these large shrimp 

 entered the fishery from the deep waters offshore seems remote. 



Migration of shrimp from North Carolina to the south during the fall 

 suggests their absence from these waters during a part of each year. Out-of- 

 season trawling by the "Pelican" in 1940, the Reliance in 1948, and the Penny 

 in 1949 has failed to reveal the presence of more than a few shrimp in North 

 Carolina in early spring. Although the bathymetric (depth) limit attained 

 by the latter two vessels is less than that at which shrimp were taken by 

 Burkenroad, the "Pelican" made hauls covering the entire continental shelf 

 in March of 1940. That year, however, failed to produce a spring fishery. 

 The possibility, therefore, that shrimp in off season may exist in the deeper 

 waters off North Carolina must be admitted, although the weight of evi- 

 dence is against it. P. duorarum (see below) is an interesting exception. 



No information has been published on the geographic distribution of 

 larval forms, and spawning areas have not been located in the Atlantic 



