The 1990 National Shellfish Register 



Major Causes of Declines in Land- 

 ings. Despite long-standing evidence 

 supporting greater restraint, over- 

 harvest remains a significant cause of 

 decline in natural shellfish stocks 

 (Kennedy, 1983). Disease and 

 pollution are also major concerns 

 among natural harvesters and aquac- 

 ulturists. For example, after MSX and 

 Dermo reduced oyster populations in 

 Chesapeake Bay, traditional seed 

 beds in the James and Choptank 

 rivers were opened. This placed the 

 remaining harvestable population at 

 risk of being entirely eliminated 

 (Hargis and Haven, 1988). 



Disease. Beginning in the 1950s, the 

 parasitic diseases MSX and Dermo 

 attacked oyster populations along the 

 Atlantic and Gulf coasts. Since 1957, 

 many significant mortalities have 

 occurred, especially during periods of 

 drought and high salinity. Entire 

 populations have been wiped out in 

 several estuaries. There has been 

 some success in producing MSX- 

 resistant strains through selective 

 breeding, but these strains were not 

 resistant to Dermo in Chesapeake 

 Bay (Ford, pers. comm.). In recent 

 studies of shellfish mortality, viruses 

 have also been found as causative 

 agents (Comps, 1988). Preliminary 

 findings suggest that the ability of 

 shellfish to withstand such infections 

 is compromised by environmental 

 pollutant stresses (Anderson, 1988). 



Pollution. Harvest areas are classified 

 as approved if pollution levels are 

 below minimum coliform standards. 

 Many states reported that areas 

 containing harvestable stock (or which 



have the potential for aquaculture, 

 especially on the Pacific Coast) were 

 closed or downgraded due to bacterial 

 levels or the lack of supporting 

 sampling data. In addition, shellfish 

 continue to be routinely stressed by 

 low oxygen events caused by nutrient 

 inputs from urban and rural sources 

 (Chesapeake Executive Council, 

 1989). Chemical contaminants cause 

 direct damage to shellfish, including 

 death and reduced recruitment 

 (Bender and Huggett, 1988). Im- 

 proved shellfish management and 

 replenishment programs are not likely 

 to overcome these problems, and 

 aquaculturists may not be able to use 



Table 6. Status of Shellfish 



Management Programs, 

 1990 a 



State Areas Acres Acres Acres/ 

 Managed Classified Sampled Sampling 

 (x 1.000) (%) Station 



a. Estuarme shellfish-growing waters only. 



10 



