o 



Our analyses suggest that prevalences of less than 

 5% may represent expected background levels of 

 shell disease in inshore populations, probably 

 related to mechanical damage or wound healing. 

 Prevalences of over 15%. as noted in some inshore 

 samples of lobsters and rock crabs, may reflect 

 pollution-related disease superimposed on the 

 natural occurrence of shell disease . Direct 

 observations on gross signs of disease enable us 

 to determine the prevalence of shell disease, but 

 laboratory studies are needed to determine whether 

 microbial agents or toxic wastes (or both) are 

 responsible for the incidence noted in New York 

 Bight apex populations. 



Shell disease has been reported in offshore 

 (>200 m) crustacean populations, including those 

 in shelf canyons, but data are limited, and there 

 is no conclusive evidence that would associate 

 shell disease in such populations with pollution 

 of offshore habitats. 



Mortalities from shell disease have been observed, 

 occasionally at high levels, in impounded 

 crustacean populations. Destruction of gills and 

 adhesions of the shell which prevent molting have 

 been considered to be responsible factors, as have 

 secondary systemic infections which develop after 

 perforation of the chitinous integument. There is 

 no specific evidence, however, that would link 

 crustacean population fluctuations in the New York 

 Bight with the presence or severity of shell 

 disease . This does not imply that such a 

 relationship could not exist -- but only that data 

 are not available for evaluation. Shell disease 

 may predispose crustaceans to mortality, but there 

 is little evidence for a direct cause and effect 

 relationship. Furthermore, there is no currently 

 available method to separate disease-caused 

 mortality from that caused by other influences. 



VI 



