Blue crab, continued 



gar (Lepisosteus oculatus), and largemouth bass 

 (Micropterus salmoides)(Lambou 1961). The primary 

 mammalian predator (other than humans) is the rac- 

 coon (Procyon lotor) (Steele and Perry 1 990, Killam et 

 al. 1992). Avian predators include the clapper rail, 

 great blue heron, American merganser, and hooded 

 merganser. Other vertebrate predators include the 

 Kemp's ridley sea turtle and the American alligator 

 (Byles 1989, Piatt et al. 1990). 



Factors Influencing Populations : Natural mortality rates 

 of juvenile (5-20mm CW) blue crab have been esti- 

 mated at 70-91 %/day in Alabama, 68-88%/day in 

 Virginia, and 25-38%/day in New Jersey (Heck and 

 Coen 1995). Estimated natural mortality rates were 

 lower at sites with seagrass, and higher at sites with 

 sand substrate. Estimation of fishery mortality is com- 

 plicated by: (1 ) the lack of data on incidental harvest by 

 non-directed fisheries, (2) inadequate recreational catch 

 statistics, and (3) widespread under-reporting of soft 

 and hard crab harvest (Adkins 1 972b, Steele and Perry 

 1 990). In addition to catches made by the recreational 

 and commercial fisheries, large numbers of blue crabs 

 are harvested incidentally by the shrimp trawl fishery 

 (Adkins 1972b, Steele and Perry 1990). At present, 

 increases in fishing effort have resulted in only slight 

 declines in catch per fisherman, indicating that the 

 fishery has remained fairly stable. Destruction of 

 wetland habitat due to dredging, filling, impoundment, 

 flow alteration, and pollution has been suggested to 

 cause a decrease in fishery production, and, therefore, 

 may be a significant factor in determining blue crab 

 production (Steele and Perry 1990). 



The blue crab can be infected by several diseases 

 caused by viral, bacterial and fungal agents that result 

 in mortality or morbidity (Steele and Perry 1 990, Messick 

 and Sinderman 1992). A variety of ecto-commensal 

 symbionts and parasites are associated with blue 

 crabs (Perry pers. comm.). Heavy infestations of 

 symbionts may interfere with metabolic processes. 

 Infested crabs are more vulnerable to predations, and 

 less tolerant of unfavorable environmental conditions 

 (Overstreet 1978). The cypris stage of the parasitic 

 sacculinid barnacle, Loxothylacus texanus, infects soft 

 juveniles retarding their growth (Overstreet 1978, 

 Overstreet et al. 1983, Hochberg et al. 1992), and 

 resulting in their loss to the fishery (Adkins 1972a). 

 Predation and cannibalism may significantly affect 

 abundance (Adkins 1972a, Heck and Coen 1995). 

 Abiotic environmental variables may affect survival 

 directly or indirectly. Mortality of blue crabs exposed to 

 low dissolved oxygen coupled with high temperatures 

 is common during the summer (May 1973, Tagatz 

 1 969). Abiotic factors can influence blue crab popula- 

 tions indirectly through predator-prey relationships if 

 they exert a greater influence on the distribution of food 



organisms than they do on the blue crab (Laughlin 

 1982). 



Personal communications 



Martinez, Janet. U.S. Army Corps of Engineers, 

 Galveston, TX. 



Lowery, Tony A. NOAA/NOS SEA Division, Silver 

 Spring, MD. 



Perry, Harriet M. Gulf Coast Research Lab., Ocean 

 Springs, MS. 



References 



Adkins, G. 1972a. Notes on the occurrence and 

 distribution of the rhizocephalan parasite (Loxothylacus 

 texanus Boschma) of the blue crabs (Callinectes 

 sapidus Rathbun) in Louisiana estuaries. Louis. Wildl. 

 Fish. Comm. Tech. Bull. No. 2, 13 p. 



Adkins, G. 1972b. A study of the blue crab fishery in 

 Louisiana. Louis. Wildl. Fish. Comm. Tech. Bull. No. 3, 

 57 p. 



Alexander, S.K. 1986. Diet of the blue crab, Callinectes 

 sap/dusRathbun, from nearshore habitats of Galveston 

 Island, Texas. Texas J. Sci. 38:85-89. 



Bass, R.J., and J.W. Avault, Jr. 1975. Food habits, 

 length-weight relationships, condition factor and growth 

 of juvenile red drum, Sciaenops ocellatus, in Louisi- 

 ana. Trans. Am. Fish. Soc. 104:35-45. 



Benson, N.G., (ed.). 1982. Life history requirements 

 of selected finfish and shellfish in Mississippi Sound 

 and adjacent areas. U.S. Fish Wildl. Serv. Biol. Rep., 

 FWS/OBS-81/51,97p. 



Bland, C.E., and H.V. Amerson. 1974. Occurrence 

 and distribution in North Carolina waters of 

 Lagegenidium callinectes Couch, a fungal parasite of 

 blue crab ova. Chesapeake Sci. 15:232-235. 



Bookout, C.G., and J.D. Costlow. 1975. Effects of 

 mirex on the larval development of blue crab. Water, 

 Air, Soil Pollut. 4:113-126. 



Bookout, C.G., J.D. Costlow, and R. Monroe. 1976. 

 Effects of methoxychlor on larval mud-crab and blue- 

 crab. Water, Air, Soil Pollut. 5:349-365. 



Bookout, C.G., J.D. Costlow, and R. Monroe. 1980. 

 Kepone effects on larval development of mud-crab and 

 blue-crab. Water, Air, Soil Pollut. 13:57-77. 



103 



