Known range. — Chesapeake Bay through Gulf 

 of Mexico and West Indies to Brazil ; Bermuda ; 

 West Africa, from Mauritania to Angola. 



"Form A," Chesapeake Bay to Campeche, Mexi- 

 co; Bermuda. "Form B," Cuba through West 

 Indies to Brazil ; West Africa. 



Remarks. — Penaeus duorarum, one of the west- 

 ern Atlantic littoral penaeids extensively utilized 

 for food, is caught in commercial quantities 

 throughout much of its geographic range (North 

 Carolina to Nicaragua and perhaps Brazil (Lind- 

 ner, 1957) ) . Distribution of this species is by no 

 means uniform, consequently the fisheries are con- 

 centrated at diverse points, some of these being 

 North Carolina, Key West, Fla., and Campeche 

 Banks, Mexico, with the latter two being by far 

 the largest. At other points in the range, the 

 species is not abundant enough to support a fishery 

 worthy of note. 



A number of recent studies, especially in 

 Florida, have greatly enhanced our knowledge of 

 this species but only a brief summary is appropri- 

 ate here. 



In North Carolina, roe-bearing females and 

 mature males appear in commercial catches from 

 the ocean near Beaufort. Inlet in May (Broad, 

 1950; Burkenroad, 1949; Williams, 1955a) and 

 they continue to occur into July. Mature ovaries 

 are blue-green in color. One spawning season a 

 year is indicated for this, the northernmost breed- 

 ing population of the species. There is strong 

 evidence, that this population is endemic. 



In Florida, Cummings (1961) found stages of 

 maturation in the ovaries of P. duorarum females 

 similar to those in P. Setiferus; i.e., the ovary pass- 

 ing through a flaccid undeveloped stage, a de- 

 veloping stage containing larger ova, a nearly ripe 

 stage in which the ovary is large, visible from the 

 outside and glaucous in color, and a ripe stage in 

 which the ova contain characteristic rodlike re- 

 fractive bodies, and finally a difficult -to-determine 

 spent stage. The highest rate of spawning was 

 judged to extend from April through July, a 

 period comparable to that in North Carolina, but 

 ripe and nearly ripe females were found at other 

 times of year as well (see also Eldred, Ingle, 

 Woodburn, Hutton, and Jones, 1961). Cummings 

 indicated that multiple spawning probably occurs. 

 Eldred, Ingle, Woodburn, Hutton, and Jones 

 (1961) postulated that mating behavior is possibly 



related to migratory behavior and that spawning 

 is initiated at minimal bottom temperatures of 

 23.9° C. (see also Cummings, 1961). They sug- 

 gested that annual temperature ranges within cer- 

 tain poorly understood, but not fatal, limits may 

 have a controlling influence on population size in 

 the following year. 



The egg and larval stages of P. duorarum were 

 described in detail by Dobkin (1961) from ma- 

 terial taken from the Dry Tortugas fishing 

 grounds. Viable, yellow brown, opaque eggs, 

 0.31-0.33 mm. in diameter, were obtained from 

 mature females spawning in the laboratory. The 

 act of hatching required 2 to 3 minutes. Dobkin 

 described five naupliar, three protozoeal, three 

 mysis, and a number of postlarval stages. The 

 naupliar and first protozoeal stages were reared 

 in aquaria, but remaining stages were taken from 

 plankton. 



Post larvae of P. duorarum have been distin- 

 guished from those of P. aztecus by Williams 

 (1959), and more fully described by Dobkin 

 (1961). The recruitment period in North Caro- 

 lina, extending from late May to November, agrees 

 well with the occurrence of ripe adults in the fish- 

 ery prior to and during the early part of this 

 period, and it also suggests that movement and 

 development time of larvae is about the same as 

 that found in P. setiferus (i.e., 2 or 3 weeks). 

 Bearden (1961) found a few postlarval P. duor- 

 arum from May through September in South 

 Carolina. 



Once on the nursery grounds in estuaries, the 

 young undergo rapid growth. Williams (1955a) 

 estimated an average increase in length of young 

 shrimp at 52 mm. per month (about 1.8 mm. per 

 day) for warmer months. More recent work shows 

 that this estimate may be too high. Eldred, Ingle, 

 Woodburn, Hutton, and Jones (1961) found that 

 pink shrimp spawned in late March or April 

 could reach lengths of 45-65 mm. by July, while 

 those spawned in May could reach lengths of 

 25-35 mm. by July. Iversen and Jones (1961) 

 showed that a 103-mm. shrimp will grow 7 mm., 

 a 130-mm. shrimp will grow 5 mm., and a 153-mm. 

 shrimp will grow little or none in a month in 

 either summer or winter. Eldred, Ingle, Wood- 

 burn, Hutton, and Jones (1961) estimated that 

 a 140-mm. shrimp is about 1 year old and that 

 on such basis shrimp measuring 200 mm. in 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



23 



