Reliahle separation of tlie larvae of CalJinectes 

 sapidu-s from tliose of other species of CalUnectes 

 is not yet possible. Because C. slmJIi.s and O. 

 oni(tfii') are coinmon in the lower 40 km. of the 

 river and in the ocean off the river's mouth 

 (Williams, 1966), and their spawninjr seasons 

 coincide with that of O. .sapid ii.'^. larvae of Calli- 

 nectc>< were designated by <Tenus only. 



A 21-m.-lony seine with a funnel-shaped bag 

 (4-mm. stretched me.sh) and a •2.5-m.-wide trawl 

 (tail bag was 0-mm. stretched mesh) were used to 

 determine the distribution of juvenile blue crabs in 

 the St. Johns Kiver. In addition to extensive 

 random sampling (1961-63), certain areas were 

 sampled at '2-week intervals (1962-63). 



Tlie stomachs of 695 blue crabs 5 to 200 mm. 

 wide were obtained from December 1962 to August 

 1963 for the food .study. Crabs were selected from 

 samples taken during scheduled collecting with a 

 seine and trawl. The percentage frequency of each 

 class of organism was determined. For each 

 stomach, the percentage of each food type in the 

 total volume of food was estimated. 



Aquatic plants, fish, and invertebrates obtained 

 in the nets and with a Petersen dredge were 

 counted to indicate natural abundance of foods 

 selected by crabs, and rei^re.sentative specimens 

 were preserved for comparison with stomach 

 contents. 



THE ST. JOHNS RIVER 



The St. Jolms Eiver lies entirely within Florida- 

 It rises from headwater marshes 80 km. north 

 of Lake Okeechobee and 24 km. inland from 

 Florida's east coast, flow.s north for 420 km. to 

 Jacksonville, and continues east 40 km. to the 

 Atlantic Ocean. North and south jetties extend 

 from the mouth of the river about 1.5 km. into the 

 ocean. Along its course the river receives the flow 

 of many tributaries and often expands into lakes. 

 Its largest tributary is the 200-km.-long Oklawaha 

 River (172 km. upstream) ; its largest lake is 9.5- 

 km. wide and 19-km. long Lake George (185 km. 

 upstream). The Intracoastal Waterway intersects 

 the river 8 km. from the mouth. The St. Johns 

 Eiver is less than 1.5 km. wide from the jetties to 

 11 km. upstream, 1.5 to 5 km. wide from this point 

 125 km. upstream to Palatka (except for a narrow 

 section at Jacksonville), and 1.5 km. wide from 

 Palatka upstream 145 km. to Sanford. Upstream 



from Sanford, the greatest width is less than 1 km. 

 The depth of the river channel is 10 m. from the 

 mouth to Jacksonville, 4 m. to Palatka, and 3.5 m. 

 to Sanford. 



Characteristics of the St. Johns River are low 

 gradient, extensive tidal influence, and varying 

 salinity and temperature. The river drops only 

 about 6 m. in the 460 km. from its source to the 

 ocean and hn ^ a slow current. The usual head of 

 tidal influence is Lake George, 185 km. upstream. 

 Salinity readings 15 km. fi'om the mouth of the 

 ri\'er ranged from 2.5 to 33.4 p.p.t. (parts per 

 tliousand) during 1961-62. They varied with 

 depth, direction of the tide, and season (salinity 

 was lowest in late summer and highest in late 

 spring). South of Jacksonville, 40 km. from the 

 mouth, salinity is normally le^s than 1 p.p.t. Water 

 temperature between the mouth and Jacksonville 

 ranged from a winter low of 8.2° C. to a summer 

 high of 34.1° C. 



ADULT CRABS 

 SEX COMPOSITION 



Most of the blue crabs of commercial size 

 (larger than 120 mm.) caught during most of the 

 year in the lower river were females, but males 

 were always dominant in the upper river. Among 

 crabs caught in the first 24 km. of the lower river, 

 60 to 90 percent were females in January to Sep- 

 tember and 10 to 25 percent in October to Decem- 

 ber. In the next 24 km. of river, extending to 8 

 km. south of Jacksonville, females made up 75 per- 

 cent of the catch in December to Feltruai'y and 15 

 to 55 percent in March to November. From a point 

 about 8 km. above Jacksonville to Palatka the per- 

 centage of females ranged during the year from 

 10 to 35 percent; and above Palatka, from 5 to 

 35 percent. 



Except in the fall when large numl)ers of males 

 occasionally were captured very close to the jetties, 

 nearly all of the adult blue crabs caught in the 

 ocean were females. 



MATING AND SIZE AT SEXUAL MATURITY 



Female blue crabs mate once, after the last in a 

 series of molts, but males may mate during each of 

 their last three growth stages (Truitt, 1939). Be- 

 fore mating, the male carries the female beneath 

 him, often for more than 2 days, mitil she sheds 

 her inunature shell. Sperm from the male is then 



BIOLOGY OF BLUE CRAB IN ST. JOHNS RIVER, FLORIDA 



19 



