OYSTER MORTALITIES ELSEWHERE 

 IN NORTH AMERICA 



Extensive as these recent mortalities in 

 waters of the Middle Atlantic States have been, 

 they form only part of a larger problem. 

 Actually, mass mortalities of oysters have 

 been occurring on most of the coasts of North 

 America, and elsewhere in the world (Sinder- 

 mann, 1966). American or eastern oysters are 

 distributed from Prince Edward Island, 

 Canada, southward to the Gulf of Mexico, with 

 major gaps in New England. With few exceptions 

 (such as upper Chesapeake Bay), mostof these 

 oyster populations harbor one or more seri- 

 ous pathogens, and many areas have had 

 mortalities. 



One disease with a history of long and 

 frustrating scientific study was first observed 

 in 1915 in oysters of Prince Edward Island, in 



the Gulf of Saint Lawrence, and has since been 

 called "malpeque disease." From 1915 to 1933 

 the disease spread around the Island, destroy- 

 ing most of the oyster stocks--some of which 

 required 20 years to return to previous levels 

 of abundance (Needier and Logie, 1947; Logie, 

 1956). During the outbreak period, oysters 

 apparently developed resistance to an unknown 

 causative organism. Beginning in 1955, mortal- 

 ities, probably due to the same disease, began 

 in waters of the adjacent mainland of New 

 Brunswick across Northumberland Strait (fig 

 7A). Oyster populations along the entire 

 northern coast of New Brunswick and Nova 

 Scotia were decimated, but mass transfer of 

 disease-resistant oysters from Prince Edward 

 Island waters beginning in 1957 has hastened 

 the recovery of the fishery (Logie, Drinnan, 

 and Henderson, 1960; Drinnan and England, 

 1965). 



Figure 7.--The distribution of oyster diseases and pathogens on the Atlantic coast of North America: (A) malpeque 

 disease; (B) Minchinia costalis ; (C) M_. nelsoni ; and (D) Dermocystidium marinum. 



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