Table 6. — Estimated average number of crab zoeae per 

 cubic ineier of water at buoy 63 (40 km. above mouth of 

 St. Johns River) for certain ynonihs, 1961-62 

 [Number of samples each month in parentheses] 



Species 



Callinectes sp 



Eurypnnopeus sp 



Menippe sp 



Neopanope sp _, 



Panopeus sp 



Pinnixa sp 



Pinnotheres maculatus 

 Pinnotheres ostreum.. 



Portunus gibbesii 



Portunus sayi 



Rithropanopeus sp 



Sesarma sp 



Uca sp 



» Less than 0.06. 



Range 



Number 

 0- 6.1 

 0- 21.5 



0- 

 0- 

 0- 

 0- 

 0- 

 0- 

 0- 

 0- 



7 

 7.2 

 2.2 

 1.6 

 1.9 

 2.1 

 1.1 



9 



0-184. 7 

 0-132. 6 

 0-294.0 



first but some second stage. All stages occurred at 

 32, 64, and 96 km. offshore. A few zoeae were ob- 

 tained about 160 km. from shore. The relatively 

 few megalops collected were at 64 and 128 km. 

 offshore. Ca77hieefes megalops were collected di- 

 rectly off the jetties in July, however, during 

 limited sampling offshore in our study. 



In brief, sampling for larval crabs in the St. 

 Johns indicated that Callinectes was one of the 

 most abundant forms in the region near the mouth. 

 First- and second-stage zoeae entered and left the 

 lower 40 km. of river from April to October. They 

 were transported by surface and bottom currents; 

 megalops usually were confined to the bottom. 

 Early development occurs in the ocean within a 

 few kilometers of shore, and growth after the 

 second zoeal stage takes place farther offshore. 

 Some larvae return to inshore waters as megalops. 



JUVENILE CRABS 



Although juvenile blue crabs were found in 

 many localities from the mouth of the river to 

 Astor, they usually occurred in small numbers or 

 in larger numbers for short periods of time. Pre- 

 ferred habitats of those le.ss than 40 mm. wide were 

 in shallow water where the bottom consisted of 

 either muck covered with dead plant material or 

 firmer mud covered with dense growths of coontail 

 {CeratophyUum) and eelgrass (VaUisneria). Cev- 

 tain areas, where relatively large numbers of crabs 

 congregated the year round, were selected for 

 sampling at regular intervals in 1962 and 1963. 

 These areas, and distances from the mouth of the 

 St. Johns, were : Clapboard Creek (15 km.) ; Dunn 



Creek (30 km.) ; Trout River (40 km.) ; buoy 

 24, Picolata (95 km.) : and buoy 11, Palatka 

 (135 km.). 



Postlarval stages of crabs continue to molt 

 periodically until full size is attained. The mega- 

 lops molts directly into the first crab stage (2-3 

 mm. wide) , which has the general appearance of 

 the adult. Growth ceases after about 20 postlarval 

 molts. Full size is attained in about 1 year; crabs 

 shed every few days at the earliest stages and at 

 intervals of 1 month or more at later preadult 

 stages. 



Early stages of l)lue crabs (2-9 nmi. wide) 

 entered the sampling areas in the lower 40 km. of 

 river primarily as waves, beginning 5 or more 

 months after spawning began and continuing to 

 the end of the year. A few early crab stages ap- 

 peared before this time, but only the occurrence 

 of large nimibers was considered a wave. The 

 waves, except in early winter, were made up of 

 crabs predominantly 6 to 9 mm. wide and beyond 

 the initial crab stages. I collected few crabs 2 to 3 

 mm. wide during summer and fall. Escape of an 

 appreciable number of first crab stages through 

 the nets was unlikely as the catch in the stations 

 of the lower river was always mi.xed with a gi'eat 

 amount of mud and debris. 



The area of metamorphosis of the megalops to 

 the first crab stage has not been determined, but 

 transformation probably takes place most fre- 

 quently in the ocean. In the south Atlantic, most 

 CaUinectes megalops were found 64 or more kilo- 

 meters offshore (Nichols and Keney, 1963). It is 

 not surprising that we collected relatively few first 

 and second crab stages in the river if transforma- 

 tion to the first crab stage also happens beyond 64 

 km. Some megalops may enter the first crab stage 

 within the estuary, because megalops do appear in 

 the river and directly off its mouth. Two megalops 

 were collected along with early crab stages in 

 Trout River. 



The fii-st waves of early crab stages in Dunn 

 Creek and Trout River were in July 1962 and 

 September 1963. With the early waves each year, 

 abundance of individuals less than 20 mm. wide 

 increase markedly (fig. 5). Like the initial spawn- 

 ing run, the first appi-eciable occurrence of young 

 crabs was later in 1963 than in 1962. 



First and second crab stages (2-4 mm. wide) 

 predominated among early stages (2-9 mm. wide) 



26 



U.S. FISH AND WILDLIFE SERVICE 



