BIOLOGY OF THE BLUE CRAB, CALLINECTES SAPIDUS RATHBUN, 

 IN THE ST. JOHNS RIVER, FLORIDA 



By Marlin E. Tagatz, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 

 Beaufort, N.C. 28516 



ABSTRACT 



Blue crabs commonly mated from March to July and 

 from October to December in the St. Johns River; the 

 proportion of males and females that matured at a 

 small size was larger in salt water than in fresh water. 



Blue crabs spawned in the first 30 km. of river above 

 the mouth, and the eggs hatched in the ocean within 

 6 km. of shore. Spawning began as early as February 

 and continued through October. 



Some blue crabs of both sexes migrated from the St. 

 Johns River to the Intracoastal Waterway, to four other 

 rivers, and to the ocean. Among crabs tagged 40 to 19.S 

 km. above the mouth of the St. Johns River and re- 

 covered at a distance from the tagging site, 89 percent 

 of the males and 95 percent of the females were re- 

 captured downstream from the point of release. Many 

 females tagged in the ocean were recaptured in inland 

 waters throughout the year. During the spawning 



season some reentered the St. Johns River for a second 

 spawning within 15 days after their eggs hatched. 



First- and second-stage zoeae and megalops of crabs of 

 the genus Callinectes were collected as far as 40 km. 

 upstream. Of 22 kinds of crab zoeae collected near the 

 mouth, Callinectes ranked third in abundance in 1961 

 and second in 1962. 



Small blue crabs (2-9 mm. wide) entered the river in 

 waves and moved as far as 135 km. upstream. Nearly all 

 of the upstream migrants were beyond the first post- 

 larval stages except during early winter. 



Blue crabs 5 to 200 mm. wide fed principally on 

 mollusks (primarily clams and mussels), fish, and 

 crustaceans (primarily amphipods and crabs). 

 Generally, they ate the same type of food regardless of 

 crab size, area, and season. 



This report presents the results of studies in 

 1961-63, on the biology of the blue crab, Calli- 

 nectes sapidus Rathbun, in the St. Jolins River. 

 Detailed information on their biology is necessary 

 to learn which factors affect the harvestable 

 population. 



The blue crab supports important fisheries along 

 the Atlantic and Gulf coasts of the United States. 

 Landings in 1950-65 averaged about 58 million kg. 

 per year. The 1965 catch was 71 million kg., worth 

 slightly more than $12 million to the fishermen. 

 In the St. Johns River, 109 fishermen, using pots 

 and 52 fishing trawls, caught 1,465,840 kg. of blue 

 crabs during 1962 (Tagatz, 1965). 



The biology of the blue crab has been investi- 

 gated extensively in Chesapeake Bay (Hay, 1905; 

 Churchill, 1919; Truitt, 1939; Pearson, 1948; and 

 Van Engel, 1958), and to a lesser degree in Dela- 

 ware (Porter, 1956), Louisiana (Darnell, 1959), 

 and Texas (Daugherty, 1952; Pounds, 1961). No 



Published June 1968. 



FISHERY BULLETIN: VOL. 67, NO. 1 



investigation has been reported, however, of the 

 biology of the blue crab in the St. Johns River or 

 ill other Florida waters. 



Blue crabs occur far upstream in the St. Johns 

 River, at least as far as Lake Harney, 305 km. 

 above the mouth (Moody, 1963) . Their widespread 

 distribution in the fresh-water portion of the 

 river is thought to be largely due to the abundance 

 of calcium chloride in the water and to the pres- 

 ence of the salt springs that drain into the river 

 (Odum, 1953). In other estuaries, blue crabs sel- 

 dom penetrate far into fresh water (Williams, 

 1965). Our studies on the St. Johns River ex- 

 tended 215 km. upstream to Astor, the terminus 

 of the commercial fishery for crabs (fig. 1). 



MATERIALS AND METHODS 



Sampling and tagging were conducted to de- 

 termine the size, sex composition, sexual maturity, 

 distribution, and movements of adult blue crabs. 



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