Figure 1. — St. Johns River, Fla., from mouth to Astor. 

 ( Circled numerals indicate buoys referred to in text.) 



In 1961 and 1962, 92 samples of about 150 crabs 

 each were obtained from the unculled commer- 

 cial catches of crabs in the river, and on 1 or 2 

 days each month, crabs were observed in catches 

 of shrimp trawlers fisliing 1 to 8 km. offshore be- 

 tween Fernandina Beach and Ponte Vedra 

 Beach. Samples were taken monthly with 

 a 3-m.-wide trawl at selected stations in the river 

 to supplement data from the fishei-y. Size, re- 

 corded as width, is the distance between the tips 

 of the large lateral spines of the carapace. 



I examined females and every fifth male crab 

 in samples from conmiercial catches for sexual 

 maturity, which is more obvious in the female 

 blue crab than in the male — the apron (abdomen) 

 is semicircular in mature females and triangular in 

 immature females. I also examined every fifth ma- 

 ture female to determine stage of ova development. 

 The shape of the apron of the male does not 



18 



change at maturity ; I based maturity in males on 

 the development of the anterior and middle vasa 

 deferentia. In the mature male the vasa deferentia 

 are large prominent ducts and the middle vas 

 deferens is bright pink. In the immature male 

 the vasa deferentia are small and the middle vas 

 deferens is white. 



From April 1961 to April 1963, 8,927 blue 

 crabs (6,383 males, 2,544 females) were tagged in 

 the St. Johns River and 2,595 (58 males, 2,537 

 females) in the ocean off the mouth of the river, 

 1.5 to 5 km. offshore and 1.5 km. north to 11 km. 

 south of the jetties. I obtained these crabs from 

 commercial fishermen. Only mature females and 

 males wider than 135 mm. were tagged; maturity 

 of males could not be determined by external 

 observation. Each tag was plastic, bore a number, 

 and was fastened by stainless steel wire between 

 the large lateral spines of the carapace (fig. 2). 

 Cronin (1949) reported that this method of tag- 

 ging was more effective than others he tested. 



I collected lai-val crabs in the St. Johns River in 

 1961 and 1962, using Clarke-Bumpus samplers for 

 simultaneous collections at the surface (0.3-m. 

 depth) and bottom (10 m.). Collections, water 

 temperatures, and salinities (surface and bot- 

 tom) were obtained hourly over any selected 4- to 

 11-hour period. Captured plankton was placed in 

 jars which were then filled to capacity (135 ml.) 

 by addition of water. Crab larvae were identified 

 and counted in three 4-ml. subsamples removed 

 from each jar. 



Figure 2. — Blue crab with carapace tag attached. 



U.S. FISH AND WILDLIFE SERVICE 



