transferred to the spermathecae of the female 

 where it remains viable a year or more and is used 

 for repeated spawnings. 



Mating blue crabs were commonly observed 

 from 11 to 215 km. above the mouth of the river. 

 Primary mating areas were the shallower near 

 shore waters of the main river and tributary 

 streams. Mating occurred sparingly in January 

 and February, was common in March to July, de- 

 creased sharply in late summer, and was common 

 again in October to December. Among 25 ran- 

 domly collected mating pairs tliat I measured, the 

 smallest, male was 1-21 mm. and the smallest female 

 was 71 mm. 



Maturity of blue crabs is attained at varying 

 widths. The jiroportion of male and female crabs 

 that matured at a small size was larger in salt 

 water (from the mouth of the river to Jackson- 

 ville) than in fresh water (south of Jacksonville, 

 table 1). The smallest mature female measured in 

 the St. Johns River was 99 mm. and the largest 

 immature female was 177 mm. Mature females be- 

 lieved to be C(iII/7ierfes fiapidnx have been captured 

 in North Carolina as small as 52 mm. (Fischler, 

 1959), but to my knowledge no immature female 

 as large as 177 mm. has been reported for any 

 other area. Overlap in the size ranges of immature 

 and mature females in the St. Johns River was 

 considerably greater than reported by Tyler and 

 Cargo (1963) for Chesapeake Bay; their smallest 

 mature female was 118 mm. wide and the largest 

 immature female was 135 mm. 



Table 1. — Percentage of mattire male and female blue 

 crabs in samples of commercial catches from the lower 

 St. Johns River (salt water) and from the tipper river 

 (fresh water), 1961-62 



SPAWNING 



Intervals between mating and spawning of blue 

 crabs, or migrations preparatory to spawning, 

 vary with season. Spawning usually takes place 

 within 1 to 2 months after mating in spring and 

 summer. If crabs mate during fall or winter, 

 spawning is delayed until warmer temperatures 

 the following spring. Most mature females of the 

 upper river migrate downstream to near Jackson- 

 ville (about 30 to 55 km. above the mouth) for 

 maturation of the ovaries. In spring and fall, al- 

 most all females make the migration soon after 

 mating and during early development of the 

 ovaries. In summer and winter, however, more 

 mature females delay migration downstream, and 

 20 to 50 percent of those in the upper river have 

 large ovaries with well-developed eggs. 



Most blue crabs spawn in the lower 32 km. of the 

 river. Relatively few females spawn near Jackson- 

 ville, and I observed no spawning south of there. 

 The eggs, numbering between 1 and 2 million and 

 known as a sponge, are deposited on the abdominal 

 appendages and carried by the female until they 

 hatch. They are initially yellow-orange, but as the 

 larvae develop and absorb the yolk during the 2 

 weeks required for hatching, the eggs become 

 brown and finally black. 



Spawning occurs in the St. Johns River 8 or 9 

 months of the year; only the very coldest winter 

 months are excluded. In 1962, sponge crabs first 

 appeared in the lower 32 km. of the river in Feb- 

 ruary, were most abundant from March to Sep- 

 tember (when 40 to 82 percent of the mature 

 females collected were with sponge), and were 

 present through October. In 1963, sponges did not 

 appear until March, probably because of the colder 

 water in February. Water temperature in 1962 in- 

 creased from an average of 13.2° C. in January to 

 18.4° C. in February. In 1963, water temperature 

 decreased from 12.9° C. in Januaiy to 11.4° C. in 

 February ; in March it rose to 20.4° C. 



As the eggs develop, the females move from the 

 river into the ocean where the eggs hatch. Almost 

 all of the sponges of river females are yellow- 

 orange, whereas most sponges on blue crabs in the 

 ocean are dark brown or black. Sponge crabs were 

 first common in the ocean in March or April but 

 only within 1 km. of shore at the river mouth. As 

 the spawning season progressed, egg-bearing fe- 

 males were found over a wider and wider ocean 



20 



U.S. FISH AND WILDLIFE SERVICE 



