Stone crab, continued 



93 day period. Fecundity is higher in larger females 

 (Sullivan 1979). 



Growth and Development 



Egg Size and Development : Fertilized eggs are main- 

 tained by the female until hatching, usually 9 to 1 4 days 

 (Lindberg and Marshall 1984). The embryonic dura- 

 tion of eggs held in the laboratory at temperatures of 29 

 to 30°C was approximately 10 days (Yang 1971). 



Age and Size of Larvae : Stone crabs typically pass 

 through five (sometimes six) zoeal stages with one 

 molt per stage, and then metamorphose into 

 megalopae. Each zoeal stage lasts three to six days 

 (Porter 1960), and total time from hatch to metamor- 

 phosis is 21 to 28 days (Brown et al. 1992). Fastest 

 larval growth of Florida stone crabs was achieved in the 

 laboratory at 30°C and 30-35%o, in which the megalopal 

 stage was reached in 1 4 days and first crab stage in 21 

 days (Ong and Costlow 1970). At 25°C and 30%o, 

 laboratory-reared gulf stone crab megalopae devel- 

 oped in 17 days (Martin et al. 1988). Development of 

 planktonic larvae to first crab stage usually requires 27 

 to 30 days, but may be affected by diet. The megalopal 

 stage of gulf stone crab is thought to last 4 to 7 days 

 (Stuck and Perry 1992). 



Juvenile Size Range : Megalopae metamorphose to 

 juveniles and settle at 1.5 to 2.0 mm carapace width 

 (CW) (Bert et al. 1986). Intermolt period for post- 

 settlement juveniles <10 mm CW is approximately 36 

 days (Brown et al. 1 992). Juveniles molt several times, 

 and growth can vary from 1 to 40 mm CW in their first 

 year. At a size of about 35 mm CW, the carapace 

 shape transforms to the adult coloration. Size in- 

 creases in increments of approximately 1 5% per molt. 



Age and Size of Adults : 



Female M. mercenaria begin to reach sexual maturity 

 at about 40 mm CW and some mate during the winter 

 at age 1 , although most mature later at age 2 (60-70 

 mm CW) or age 3 (70-80 mm CW). Males are generally 

 mature at 70 mm CW, at age 2. In laboratory studies, 

 measured growth of adults has been approximately 1 5 

 to 20% of the carapace width per molt, which is 

 comparable with field growth observations (Simonson 

 1 985, Tweedale et al. 1 993). After four years of age, 

 crabs generally molt only once per year, typically in the 

 fall. Terminal molts have been suggested to occur 

 around 1 1 2 mm CW, but crabs can reach sizes of 1 30 

 to 145 mm CW (Bert et al. 1978, Sullivan 1979, 

 Lindberg and Marshall 1 984, Bert et al. 1 986). Recruit- 

 ment into the Florida stone crab fishery probably oc- 

 curs at about age 2 (Ehrhardt and Restrepo 1989, 

 Restrepo 1989). The maximum age of Florida stone 

 crabs has been estimated as six to eight years or more 

 (Bert et al. 1 986, Restrepo 1 989). Gulf stone crabs are 



morphometrically similar to Florida stone crabs, and 

 their carapace widths at 50% sexual maturity have 

 been estimated at 71 mm for males, and 73 mm for 

 females (Perry et al. 1995). 



Food and Feeding 



Trophic Mode : Stone crabs are high trophic level 

 predators and are primarily carnivorous at all life stages 

 (Bert and Stevely 1989). After feeding to satiation, 

 these crabs can live for two weeks without feeding 

 again (Bert et al. 1986). 



Food Items : It has been suggested that larvae have 

 specific dietary requirements, apparently met by only 

 certain types of planktonic animals (Guillory et al. 

 1995). Juveniles feed on small molluscs, polychaete 

 worms and crustaceans. Juveniles in captivity are 

 known to consume small bivalves, oyster drills, beef 

 liver and chicken parts, polychaetes, and each other. 

 Adults use their heavy chelae to crush all types of 

 molluscs, and are known to prey on oysters (Williams 

 1984, NOAA 1985, Bert et al. 1986) and mussels 

 (Brachidontes spp.) (Powell and Gunter 1968). Stone 

 crabs are also known to consume carrion and veg- 

 etable matter such as seagrass (NOAA 1985). 



Biological Interactions 



Predation : Larvae are preyed on by other planktivores, 

 while the larger juveniles are prey for black sea bass, 

 groupers, common octopus (Octopus vulgaris), and 

 other large predators (Lindberg and Marshall 1984, 

 Lindberg et al. 1992). Adults can usually defend 

 against predators, but may be vulnerable to attack 

 when caught in crab traps. 



Factors Influencing Populations : Although "harvested" 

 crabs are released alive, subsequent mortality of 

 declawed crabs has been estimated at 50% and has a 

 significant impact on stone crab populations. After 

 removal from traps, crabs are sometimes held onboard 

 and declawed while enroute to port; mortality of these 

 crabs is higher if they are held too long and not kept 

 moist, and if the claws are not severed along the 

 natural fracture plane (Simonson and Hochberg 1 986). 

 The Florida stone crab fishery is considered to be fully 

 exploited. Recent annual harvests have been over 

 1 ,000 metric tons per year (mt/y), although long-term 

 potential yield has been estimated as 976 mt/y (NOAA 

 1993), and Zuboy and Snell (1982) estimated a maxi- 

 mum sustainable yield (MSY) of 853 mt/y. Declines in 

 catch per unit effort (CPUE) have been observed in 

 recent years, further suggesting that the fishery is fully 

 utilized (Phares 1992). Mariculture methods have 

 been developed to produce stone crab megalopae 

 (McConnaughey and Krantz 1 992), although commer- 

 cial-scale mariculture of stone crab claws is not yet 

 feasible. 



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