WENNER AND WENNER: CRUSTACEANS FROM COASTAL HABITATS 



The mean total length of brown shrimp was great- 

 est in summer (x = 126 mm, n = 2,718) and fall 

 (x = 126 mm, n = 214) following emigration from 

 the estuaries. Size at emigration for brown shrimp 

 has been reported to be 100-105 mm (Joyce 1965) 

 and 60-103 mm (Trent 1967). Off North Carolina, 

 P. aztecus enters the commercial fishery in June at 

 a size of 100 mm (South Atlantic Fishery Manage- 

 ment Council 1981). Mean size of brown shrimp was 

 largest off Georgia (x = 138 mm, n = 871) and 

 Florida (i = 127 mm, n = 493), while those from 

 strata off North Carolina and South Carolina aver- 

 aged 119 mm (w = 1,600). The capture of larger 

 shrimp further south may result from migration of 

 individuals to waters off Georgia and Florida. These 

 shrimp are probably supplied by the sounds and 

 estuaries of North and South Carolina. Tagging 

 studies off North Carolina indicate that brown 

 shrimp move to the south and to deeper, nontrawl- 

 able waters once they leave the sounds (Purvis and 

 McCoy 1974). Shipman (1980) noted few recaptures 

 of brown shrimp tagged off Georgia and suggested 

 that lower return rates may indicate offshore move- 

 ment of brown shrimp, out of the nearshore trawl- 

 ing grounds. 



Portunus spinimanus 



This common portunid of the inner continental 

 shelf ranges from New Jersey to southern Florida 

 (Powers 1977), often co-occurring with P. gibbesii. 

 Camp et al. (1977) found P. spinimanus to be one 

 of the commonest decapod crustaceans in samples 

 from nearshore east Florida waters with salinity of 

 32-39"/oo and temperature ranging from 19.2° to 

 32°C. 



In the present study, P. spinimanus was the 7th 

 most numerous species (4.1% of the total catch) and 

 the 11th most important by weight (4%) (Table 1). 

 This species occurred at 73% of the trawl stations 

 from all seasons. The stratified mean catch per tow 

 was lowest in winter (3 individuals/tow). Catch per 

 tow values by stratum were higher in spring (13 in- 

 dividuals/tow) and summer (14 individuals/tow), but 

 decreased to 11 individuals/tow in fall (Table 5). 

 Catch of P. spinimamis per tow differed among 

 areas with most individuals collected in trawl tows 

 off Florida (15 individuals/tow). Increased abun- 

 dance in strata off Florida was observed for every 

 season except summer (Fig. 4). 



The size composition of P. spinimanus in trawl 

 catches differed between strata and seasons. 

 Mean carapace width was largest for individuals 

 collected off Florida (x CW = 54 mm, n = 974) 



and Georgia (x CW = 53 mm, n = 343), while 

 those collected in combined strata off South Carolina 

 and North Carolina averaged 46 mm CW {n = 

 1,129). Largest individuals were collected in winter 

 (i CW = 58 mm, n = 144) and fall (i CW = 56 

 mm, n = 782). The smaller average size of in- 

 dividuals collected in spring (x CW = 48 mm, n 

 = 601) and summer x CW = 46 mm, n = 919) 

 may reflect an influx of small crabs from the 

 previous fall hatch. 



Analysis of sex ratio by season indicated no sig- 

 nificant deviation from unity except during spring 

 when female P. spinimanus outnumbered males 

 (Table 6). Average size was similar for males (i 

 CW = 51.4 mm, n = 1,172) and females (x CW = 

 49.8 mm, n = 1,230). 



Ovalipes ocellatus 



This portunid crab has a broad geographic range 

 from Canada to Georgia (Williams 1984). Abun- 

 dance decreases in southern latitudes, apparently 

 in response to lessened tolerance to warm-water 

 temperatures (Vernberg and Vernberg 1970). In 

 the present study, 0. ocellatus occurred more 

 frequently than 0. stephensoni, but was not as 

 numerous (Table 1). Abundance of this crab de- 

 creased from the northern to southern area, with 

 most individuals collected in trawl catches off North 

 Carolina/South Carolina (14 individuals/tow) (Fig. 

 4). Abundance in strata off Georgia was 6 in- 

 dividuals/tow, while <1 individual/tow was caught 

 off Florida. The stratified mean catch per tow dif- 

 fered among season with most individuals collected 

 in spring (Table 5). 



Average size of 0. ocellatus differed among areas. 

 The average size of individuals collected in strata 

 off Florida was larger (x CW = 65 mm, n =11) 

 than that from other areas (Georgia: x CW = 53 

 mm, n = 588; South Carolina/North Carolina: x 

 CW = 51 mm, n = 1,340). Seasonal differences in 

 size composition were noted as well, with average 

 carapace width smallest in spring (x C W = 48 mm, 

 n = 558). This may reflect occurrence of juveniles 

 from a fall-winter hatch (Dudley and Judy 1971). 

 Average size of individuals during other seasons was 

 winter (x CW = 59 mm, n = 58), summer (x CW 

 = 52 mm, n = 966), and fall (i CW = 57 mm, n 

 = 357). 



No significant seasonal difference in sex ratio 

 was noted, with the exception of fall when females 

 were more numerous than males (Table 6). Male 

 0. ocellatus (x CW = 54 mm, n = 923) were larger 

 than females (i CW = 50 mm, n = 1,009). 



171 



