FISHERY BULLETIN: VOL. 83, NO. 1 



Unity; recorded off east Florida and off west cen- 

 tral Florida in salinities between 32.00 and 

 36.75%o and 31.22 and 36.71%o (Kennedy et al. 1977 

 and Huff and Cobb 1979, respectively) and off Mis- 

 sissippi between 27.8 and 34.6%.. (Franks et al. 

 1972). Only once, in the Chatham River, Fla., has 

 it been recorded in an estuarine environment, at a 

 salinity of 24%o (Rouse 1969). The specimens on 

 which this record is based consisted of larvae and 

 small juveniles, and might have been misiden- 

 tified, perhaps belonging to one of the other con- 

 geners found in that area. This shrimp, unlike 

 other penaeoids, does not depend upon estuarine 

 waters during its life cycle (Eldred 1959; Joyce 

 1965). 



Many investigators (Lunz 1957; Joyce 1965; 

 Brusher et al. 1972; Cobb et al. 1973; Brusher and 

 Ogren 1976; Camp et al. 1977; Kennedy et al. 1977; 

 Huff and Cobb 1979; Wenner and Read 1981) note 

 that this species is predominantly nocturnal. Cobb 

 et al. (1973) suggested that it burrows into the 

 substratum during the day, thereby avoiding pre- 

 dation and capture by trawls. 



Notes on biology and abundance. — Whereas the 

 other American rock shrimps have been largely 

 neglected, because of its considerable economic 

 value, large size, and ready availability S. bre- 

 virostris has been the subject of a number of inves- 

 tigations. Cobb et al. (1973) and Kennedy et al. 

 (1977) studied the reproductive cycle (including 

 ovarian development in detail) of west central and 

 east Florida populations, respectively They con- 

 cluded, as did Huff and Cobb (1979) who investi- 

 gated the former population, that spawning and 

 recruitment seem to occur throughout the year, 

 with a peak of spawning from October to February 

 off the west coast of Florida and during winter and 

 early spring off the northeast coast. Cobb et al. 

 (1973) suggested that a decrease in the daily 

 photoperiod was responsible for the onset of 

 spawning. 



Morphometric studies by Kennedy et al. (1977) 

 demonstrated that increase in total length occurs 

 at the same rate in males as in females until they 

 reach 20 mm cl, then the rate of increase of total 

 length in females become less. They also found 

 that the juveniles grow at an average rate of 2-3 

 mm cl per month whereas the adults grow at 0.5- 

 0.6 mm cl. It was also estimated by them that the 

 life span of this species is 20-22 mo. More re- 

 cently Arreguin Sanchez (1981) presented biologi- 

 cal fishery statistics (length/weight, growth, mor- 

 tality, etc.) for this species. 



Density of this shrimp in various populations 

 fluctuates seasonally. Wenner and Read (1981, 

 1982) found that S. brevirostris is the dominant 

 species of decapod crustacean on the continental 

 shelf between Cape Fear, N.C., and Cape Canav- 

 eral, Fla., and that highest densities occurred in 

 one summer of their 2y2-yr study. Lunz (1957) 

 noted a bimodal seasonal abundance off South 

 Carolina, with peaks occurring from September 

 through December and again in May. Kennedy et 

 al. (1977) observed that peak abundance is reached 

 during the fall in the east Florida population. In 

 the Gulf of Mexico, off central Florida (Cobb et al. 

 1973; Huff and Cobb 1979), maximum abundance 

 was found to exist from late summer through the 

 fall. Off Apalachicola, Fla., (Allen 1973) highest 

 densities seem to occur from June to October; in 

 coastal water of Louisiana (on the basis of 

 maximum production) and Texas (Brusher et al. 

 1972), from June through January, and in Bahia 

 de Campeche (Hildebrand 1955) this species was 

 more abundant in February than in July. It thus 

 appears that throughout the range of this species 

 maximum abundance occurs from summer 

 through fall, and, in some areas, into early winter. 



Kutkuhn (1962) calculated regression equations 

 for predicting "headless" from "whole" weights and 

 vice versa, and Cobb et al. (1973) presented equa- 

 tions for relating carapace length to total length 

 for males and females, as well as others for 

 carapace length and total weight for males and 

 females, and for both sexes combined. Huff and 

 Cobb (1979) also calculated the relationships of 

 carapace length to total length and carapace 

 length to weight for each sex. 



Commercial importance . — Commercial fishing for 

 S. brevirostris began in the United States in 1970 

 (Allen 1973) and since then production has in- 

 creased noticeably, amounting to 3,351,000 lb, 

 with a value of $3,222,000 in 1982 (Table 1). The 

 fishing grounds are located off the southeast coast 

 from North Carolina to central Florida (the most 



Table l. — Landings of Sicyonia brevirostris 

 by areas and their values for 1982.' 



'Data provided by tlie Southeast Fisheries Center 

 Statistical Survey Division, National Marine Fisheries 

 Service, NCAA, Miami, Fla 



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