of the catch are useful in evaluating aspects of 

 life history that have an immediate effect on 

 the fishery. Knowledge of the fishery also can 

 indicate factors that govern the size of the 

 catch. 



LIFE HISTORY OF THE BLUE CRAB 



Knowledge of the life history of the St. Johns 

 River blue crab, especially migrations of 

 adults, is needed to understand the availability 

 of crabs to the fishery. 



Early development occurs in the ocean. The 

 eggs hatch off the mouth of the St. Johns River 

 from March through October, and the young go 

 through a series of larval forms before they 

 take on the appearance of the adult. Larvae 

 reared in the laboratory went through seven 

 zoeal stages over a period of 31-49 days; 

 the one megalops stage lasted from 6 to 20 

 days (Costlow and Bookhout, 1959). 



Young crabs migrate up the St. Johns River 

 where they reach maturity in approximately a 

 year. Crabs mate in the river, especially in 

 waters of low salinity. After mating, the fe- 

 males migrate to the lower St. Johns River 

 where they produce a sponge (egg mass on the 

 abdomen); then they enter the ocean, where 

 the eggs hatch. Many spent females. return to 

 the lower St. Johns River or adjacent river 

 systems. Males may remain in the low-salinity 

 areas or migrate downriver into high-salinity 

 waters. Immature crabs move upriver and adult 

 crabs downriver throughout the year. 



THE RIVER AND THE LOCATION OF 

 THE CRAB FISHERY 



The St. Johns River watershed has an area 

 of approximately 8,350 square miles. Head- 

 water marshes are 50 miles north of Lake 

 Okeechobee and 15 miles inland from Florida's 

 east coast. The river flows north 260 miles to 

 Jacksonville, after which it continues east 25 

 miles to the Atlantic Ocean. The St. Johns 

 gradient of only about 20 feet gives the river 

 a slow current. The usual head of tidal in- 

 fluence is Lake George, 115 miles upstream. 

 During 1961-62, salinity readings 10 miles 

 from the mouth of the river ranged from 2.5 

 p.p.t. to 33.4 p.p.t. They were lowest in late 

 summer and early fall and highest in late 

 spring. South of Jacksonville, 26 miles from 

 the mouth, salinity is normally less than 1 p.p.t. 

 Water temperatures in the lower river ranged 

 from 8.2° to 34.1°C. 



The commercial fishery for blue crabs 

 beings 7 miles upstream and extends to Astor, 

 Fla., approximately 135 miles upstream from 

 the mouth of the river. The region encom- 

 passing the fishery was divided into three areas 

 to facilitate investigation, as well as to allow 

 comparison (fig. 1). 



Area 1 extends 26 miles, from the mouth 

 of the St. Johns River to the mouth of the 

 Ortega River south of Jacksonville. The width 

 in this area, for the most part, is less than 1 

 mile; the river is constricted at Jacksonville 

 into what is termed the "narrows." Channel 

 depth is 34 feet. North and south jetties extend 

 from the mouth of the river about a mile into 

 the ocean. The Intracoastal Waterway inter- 

 sects the St. Johns River 5 miles from the 

 mouth. The crab fisheries in the Waterway 

 itself were located nearer other river sys- 

 tems and were not considered as part of the 

 St. Johns River fishery. The first 7 miles of 

 river have no fishery because of swift cur- 

 rents, regulations, and heavy boat traffic. 

 The important tributaries for crabbing are 

 Clapboard Creek and Trout River. 



Area 2 encompasses 55 miles of river from 

 the mouth of Ortega River upstream to Palatka, 

 Fla. This area consists of a 1 - to 3-mile- 

 wide, shallow basin with a channel 13 feet 

 deep. Much of the fishery in this area is 

 located between Switzerland and Picolata. None 

 of the tributary streams in this area supports 

 significant crab fisheries. 



Area 3 extends 54 miles from Palatka to 

 Astor. The river in this area is narrow except 

 for widening to 4 miles to form 14-mile-long 

 Lake George, the largest lake in the river 

 system. The average depth of Lake George is 

 about 10 feet, and of the river channel 12 feet. 

 Fishing for crabs in this area is concentrated 

 between Welaka and the northern half of Lake 

 George. The Oklawaha River and especially 

 Crescent Lake support relatively important 

 crab fisheries. 



THE COMMERCIAL FISHERY 

 FOR BLUE CRABS 



Only adult hard crabs are taken in the year- 

 round blue crab fishery in the St. Johns River. 

 No soft-crab fishery has developed. Although 

 most of the catch is sold to plants for 

 processing, crabs also are sold alive to retail 

 markets and to sport fishing camps for fish 

 bait. Species of crabs other than the blue crab 

 are not significant in the fishery. 



Fishing Gear 



Two types of gear are generally used for 

 taking crabs in the St. Johns River- -the crab 

 pot and the shrimp trawl. The crab pot, the 

 most widely fished, accounts for the bulk of 

 the catch. Shrimp trawls are important only 

 in Area 1. Catches of crabs by trawl may or 

 may not be incidental to the capture of shrimp, 

 depending on seasonal abundance and market 

 demand for both species. Trotlines, dredges, 

 scrapes, and fyke nets are rarely fished. 



Crab pots are made of wood or wire (fig. 2) 

 and are baited with scrap fish. The pots are 



