curs in June and early July (Daugherty, 1952). 

 Five stages in the reproductive cycle of mature 

 females have been described (Hard, 1942), and 

 a number of authors have shown that the number 

 of eggs in an egg mass (sponge) may range from 

 700,000 to more than 2 million. 



The eggs hatch into zoeae, undergoing develop- 

 ment through seven stages. These stages have 

 been described from laboratory cultures (Cost- 

 low, Rees, and Bookhout, 1959; Costlow and 

 Bookhout, 1959). Atypically, an eighth stage may 

 occur. The last zoeal stage molts into a megalops 

 stage and this into the first crab stage. 



Churchill found that eggs hatch in about 15 

 days at 26.1° C. and slightly faster at higher 

 temperatures. Development from hatching to 

 megalops lasts from 31 to a maximum of 49 days 

 in various salinities, but development time in the 

 different stages is quite variable even in a single 

 salinity-temperature combination. The megalops 

 stage lasts from 6 to 20 days. It was found that 

 development progresses at a comparable rate in 

 salinities between 20.1 and 31.1 °/ 0o at 25° C. 

 Salinity above 31.1 °/ 00 slowed development, 

 and below 20.1 °/ 00 larvae rarely completed the 

 first molt. Larvae never went beyond the first 

 zoeal stage when reared at 20° C. and did not 

 progress beyond the third zoeal stage when 

 reared at 30° C. Once the first crab stage is 

 reached, the animals continue to molt as they 

 grow and are estimated to undergo some 18 to 20 

 or more molts before reaching maturity (Van 

 Engel, 1958). 



In Chesapeake Bay, where the crab is perhaps 

 more abundant than in other areas, it has been 

 demonstrated that crabs spawned in June of one 

 year are mature about 14 months later and at that 

 time mate. Most mating pairs are found in July, 

 August, or September, though the mating season 

 extends from May to October. At this time, fe- 

 males ready to molt into the mature stage (termi- 

 nal molt) are carried about, cradled upright, 

 under the males' bodies. Such pairs are called 

 doublers. The male frees the female during the 

 time she is actually casting the old exoskeleton, 

 but when this is shed he grasps her again, this 

 time with the ventral surfaces together, and com- 

 pletes the breeding act by introducing sperm via 

 the copulatory stylets into t he spermathecae. 

 Copulation may last for several hours. When 



sperm transfer is complete, the female is allowed 

 to resume an upright posture and is again car- 

 ried under the male for a time until her shell is 

 hardened. Males may mate more than once and 

 at any time during their last three intermolts 

 (Van Engel, 1958) ; females only do so once, but 

 the sperm supply may serve to fertilize more than 

 one mass of eggs. Usually, a female mated in late 

 summer casts the first batch of eggs the following 

 spring at an age of approximately 2 years, but 

 egg laying may be at any time from 2 to 9 months 

 after mating. A second spawning has been ob- 

 served to occur later in summer among some indi- 

 viduals, and it is possible that a third may occur, 

 possibly as late as the succeeding spring or at an 

 age of 3 years. Three years is judged to be about 

 the normal maximum age for this species. 



The life history of the blue crab is complicated 

 by the fact that it leads a migratory existence. 

 The migratory patterns have been studied in 

 greatest detail in Chesapeake Bay but the same 

 pattern appears to be true of other areas as well. 

 Mating usually takes place in water of reduced 

 salinity well up in estuaries. After this, the fe- 

 males migrate downstream to areas of higher 

 salinity near the mouths of estuaries where the 

 eggs are laid and hatched, whereas the males tend 

 to remain in the low-salinity areas for the re- 

 mainder of their lives. For this reason, samples 

 of adult crabs (or commercial catches) near the 

 sea contain greater numbers of females, whereas 

 those from the middle or upper reaches of bays 

 contain larger percentages of males except at the 

 breeding season. Once in the spawning areas, the 

 females tend to remain there for the remainder of 

 their lives or move a short way out 'to sea. Once 

 hatched, the zoeae lead a planktonic existence un- 

 til they transform to the megalops stage. As soon 

 as the crabs transform to the first crab stage, they 

 begin a migration up the estuary toward the mat- 

 ing grounds. Some early recruits may reach these 

 areas in their first summer of life, the remainder 

 early in the second year of life. In areas smaller 

 than Chesapeake Bay, there may be a certain 

 amount of overlap in mating and spawning 

 grounds but the two areas tend to be distinct. In 

 Chesapeake Bay, the spawning grounds are near 

 the mouth of the Bay; in North Carolina and 

 Louisiana, near the inlets and passes. In Texas, 



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FISH AND WILDLIFE SERVICE 



