peak year, the commercial harvest totaled almost 2.5 million lb (Table 4). 

 Recently catch per unit of effort has declined and the data indicate the 

 fishery is near the maximum substainable yield (Swingle 1977). 



Most crabs are taken in traps with about 5% caught in shrimp trawls. 

 Catch data for recreational crabbing are unavailable, but it may approach 20% 

 of the total catch (Tatum, unpubl.). The crabs ovulate and mate in Mobile 

 Bay and its estuarine system. Adult females spawn around and south of the 

 barrier islands; the larvae undergo a period of development in open gulf 

 waters. They move into the estuary when they have reached the postlarval 

 stage (Benson 1982). Larval crabs grow to harvestable size in 12 months. 



Oyster Reefs (Crassostrea virginica) 



A recent review of the American or eastern oyster ( Crassostrea virginica ) 

 fishery in Alabama by Eckmayer (1979) is the basfi For the following 

 material. The eastern oyster is the most economically important mollusk 

 species in Alabama. The oyster landing for Alabama in 1978 was 760,000 lb 

 and in 1983, 417,153 lb (Table 4). The total area of oyster reefs has 

 remained relatively constant since 1894 at approximately 1200 ha (2965 acres), 

 but has shifted southward due to environmental factors. Productivity may 

 decrease in the future due to overfishing. One of the largest reefs is Cedar 

 Point Reef (Biloxi quadrangle). This reef has been subject to major 

 fluctuations in size since it was first fished in the 1800's; in 1968 it 

 covered 563 hectares (1,391 acres). Cedar Point Reef was temporarily closed 

 in 1978 because overfishing in 1977 had severely reduced the oyster 

 population. 



Sand Reef (Biloxi quadrangle), the second largest in Mobile Bay, 

 decreased 92% from 1952 to 1968. The change was due primarily to sedimenta- 

 tion. It was spread with clam shells to increase the area, but the effort was 

 only partially successful, since some of the shells sank into the mud 

 substrate. However, by 1979 the densest oyster population in all of Mobile 

 Bay was on Sand Reef (Eckmayer 1979). 



Factors affecting oyster populations are lowered dissolved oxygen levels, 

 salinity, predators, disease, and overfishing. 



Spoil materials from dredging have covered and destroyed some parts of 

 Alabama oyster reefs in the past. Dredging for the Gulf Intracoastal 

 Waterway altered salinity in some areas. Since oysters are found mostly in 

 areas with salinities between 10 to 20 ppt, floods of freshwater from rivers 

 can result in a short-term reduction in reef populations, or even mass 

 mortalities. Apparently, though, floods have caused relatively little 

 long-term damages in Mobile Bay. The benefits of the freshwater, such as 

 control of diseases and predators, may compensate for losses to the oyster 

 population (Eckmayer 1979). 



The most important oyster predator is the southern oyster drill ( Thais 

 haemostoma), for which there is no effective man-made control. Drill 

 populations are naturally controlled by freshwater floods. Drills cannot 

 survive long periods in water less than 15 ppt salinity. When freshets 



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